"A study of the interactions between Plasma Cortisol 
levels,- Estrous cyclesy Rectal Temperatures 
and Respiratory Rates in Heifers."
by
OYEWOLE ADEYEMO (D.V.M.. Ibadan)
A Thesis S ted in the Department of Chemical Pathology 
of the Faculty of Medicine in Partial Fulfilment of the 
Requirements for the Degree of 
DOCTOR OF PHILOSOPHY 
of the
UNIVERSITY OF IBADAN
22nd June; 1978.
ii
Dedication
To Adeyelu and Gabriel Meyemo 
I5.y Loving Mother and Father ♦
iii
Abstract
The need to improve the animal protein diet of the Nigerian 
population has underlined the importation of temperate-evolved cattle 
into Nigeria. How these animals adapt to the new environment should be 
Of economic and scientific interest. Under the natural hot/humid sub­
equatorial climate of Ibadan, some physiologic, adrenocortical and 
reproductive functions were investigated in 6 German Brown, 5 Holstein * 
and 6 White Fulani heifers.
The Brown/ Holstein and Fulani heifers attained puberty at the average
f with the standard deviation^ of 17.8 + L.6, 16.7 + 1.8 and 23.7 + 1.9
months respectively. Observations on estrous cycles s-ho wed that estr~ous 
period ranged between 7 and 31 hours in the three breeds, the mean 
values, with the standard errors, being 16.2+0.7, 15.8 0.7
and 14.6 +_0.8 hours in the Brown, Holstein and Fulani heifers 
respectively. The difference between the Bos taurus and Bos indices cattle
was slicrht but sî i>&icant. Mogt estrus commenced during the day with
a greater concentration in the morning time. The intensity of estrus was 
high in both species though, occasionally, a few Fulani heifers showed 
weaker estrual signs.
Average estrous cycle length was slightly longer in the Brown and 
Fulani than in the Holstein heifers, the values, with the standard 
errors, being 21.0 + 0.3, 21.4 0.2 and 20.1 + 0.2 days respectively.
Ovulations occurred mostly within a day after estrus, and this as well
iv
as the duration of estrus and estrous cycle length showed no seasonal 
variations. There was no indication that Bos taurus and Bos indieus 
cattle under the semi-intensive management preferred any particular season 
for increased sexual activity or breeding in the sub-equatorial climate.
Marked shifts occurred in the respiratory rates during four 
selected quarters of the year. Increases occurring in the dry hot season 
from the values in the relatively cooler season were highly significant. 
Both mean morning and mean afternoon values (lU - kk and 17 - 75 
breaths per minute respectively) were highest in the Holstein and lowest 
in the Fulani heifers.
Rectal temperatures showed slight but significant seasonal changes. 
Mean values were 101.3°F (38.5°C) and 102.2°F (39.0°C) in the morning 
and afternoon respectively for all the heifers together through the
year. The lowest afternoon values occurred in the wettest and coolest 
months. The Fulani and Holstein heifers showed the lowest and highest 
mean values respectively.
Diurnal and circadian shifts in the respiratory rates and rectal 
temperatures in the heifers were most exaggerated in the sun and in the
Holsteins, the latter particularly exhibited polypnea and hyperthermia. 
Unlike the Xebu, the Bos taurus cattle sought shade in the sun. The 
Holstein heifers sought shade more frequently and stayed there longer 
than the Brown heifers.
Basal plasma cortisol concentrations at 07 - 08.00 hours, 
determined by radioimmunoassay during four quarters of the year was low,
V
ranging between 1 - 1 0  ng/ml with occasional -cycle and more 
frequent- . proestrual and/or estrual elevations. Mean values showed 
slight but significant seasonal changes. The levels in the dry season 
were slightly lower than in the wet season. Breed differences were 
not significant. Diurnal and circadian plasma cortisol concentrations 
in heifers in the shade and in the sun showed no rhythmical pattern.
Exogenous corticotrophin at and after mid-cycle stage elicited markec 
and prolonged adrenocortical response which varied between heifers, and
did not alter estrous. cycle rhythmicity. high adrenal reserve in the
heifers was indicated.
Bos taurus cattle have been found to be adaptable to the southern
Nigerian climate represented by the Ibadan condition. Management practice 
should, however, ensure all-year-round provision of shade and adequate
nutrition including the! adoption of night grazing.
The Brown cattle are recommended over the Holsteins because the 
former are more comfortable, h mixed herd of the two breeds should be
discouraged because socially the Browns dominate over the Holsteins.
The Fulani cattle are more adaptable to the subequatorial climate 
than the temperate-evolved cattle as evidenced by the physiological 
responses, artificial breeding should be suitable for the Fulani cattle 
as it is for the Bos taurug cattle. The need to adopt better management
i  :■
practices than hitherto existing, range system for the Fulani cattle^ so 
that their reproductive and productive attributes may be well 
manifested;, is indicated. <
vi
List of Abbreviations
The following abbreviations were used in this study;
ng — nanogram
pg = microgran
mg = milligram
g = gram
pg = picogram
% - per cent
°F = degree Farenheit
°C = degree centigrade
ml - millilitre
)* = microlitre
i|f = hydrogen ion
Kg = kilogram
mMol = millimole
Ci curie
pCi micro Curie
h . n hour
min . = minutes
BDH *" British Drug House
UK = United Kingdom
USA - United States of America
et al = and others
M.W. = molecular weight
max => maximum
rectal temperature
ed = edition
cpm =s counts per minute
pH = hydrogen ion concentration
S D = standard deviation
SE- standard error
vii
X = mean
im- = in tramuscular1
S ,» Significant
NS = Not significant
P.C.V.~ packed cell volume
Hb = Haemoglobin
Ta = environmental temperature Ca^Wient. 4t£npferot<Jtfej
RH% = Relative Himidity
ram = millimeter
ins = inches
LoS.D.= least significant difference
P04 = phosphate radical 
Ha + = Sodium ion
LH = Luteimsmg hormone
% 0  = Water
CL = corpus luteum
Cl = chloride radical 
K + = Potasium i°n
ACTH = Adrenocorticotropic hormone
CV = coefficient of variation
CNS = central nervous system
RIA radioimmunoassay 
C P ^  = competitive protein binding 
Fig(s)= figure(s)
CRF = corticotrophin-releasing factor
B = German Brown (as used in identifying the heifers)
H = Holstein-Friesian (as used in identifying the heifers)
F = White Fulani (as used in identifying the heifers)
viii
Steroid Nomenclature
Trivial names systematic name
cortisol, hydrocortisone llo< , 17p, 21 -trihydroxy-pregn-4-ene 3, 20-dione 
corticosterone 11<^ , 21-dihydroxy-pren-4-ene 3, 20-dione 
Progesterone Pregn-4-ene 3, 20-dione
ix
A C K N O W L E D G E M E N T
The basic planning of this investigation was by Professor Jorg 
Steinbach formerly of the Department of Animal Science and now of 
the University of Gessen, Western Germany. Dr. Everett Heath, Reader 
in the Department of Veterinary Anatomy, took over the main supervisory 
role on the departure of Professor Steinbach from Nigeria, and has been 
tremendously helpful in guiding me through the work, and in reading 
and correcting tke original manuscript. I am profoundly grateful 
to these my able supervisors.
The impetus for this work was given by' Professor B.K. Adadevoh,
currently Director of Medical Research, Nigerian Institute for Medical 
Research, Lagos, who together with Professor Steinbach, introduced me 
to research work, and whose advice and encouragement were inspiring 
throughout the period of the study. My thanks go to him and to 
Dr. E. A. Olaloku, Reader in the Department of Animal Science whose 
supervisory role has made procedures on the University farm possible.
I am grateful to Professor D. A. Olatunbosun, Head of Department 
of Chemical Pathology and of the Reproductive Biomedicine Research 
Unit for encouraging me and providing a suitable atmosphere for 
research work. Dr. A. 0. Dada of the same department has been 
tremendously helpful in the laboratory procedures; and discussions with 
him have been most useful. My thanks are due to the members of staff
of Climate Unit, Department of Geography, for supplying the meteoro­
logical data, and to Dr. Oluremi Fayemi for vasectcmising the Fulani bull
X
Solutions to statistical problems were basically due to 
Dr. 0. Ayeni and Mr. Afolabi Bamigboye, of the Department of 
Preventive and Social Medicine and to Miss Titi Akinpelu of the 
Computing Centre of the University of Ibadan. I am quite grateful 
to them all.
I appreciate the cooperation of my colleague Research Fellows 
in the department, and ray hard working assistants, Mewers Kunle
Busari and Idowu Orisadare* I wish to thank Dr. J. 0. Bolodeoku 
for German translation, the Director of the University Farm,
Mr. Roberts, and the entire staff of the Dairy Unit of the University 
farm for help in keeping and feeding the animals, and the staff of 
the Departments of Veterinary Medicine, Veterinary Parasitology and 
Microbiology for their roles in health care of the experimental 
animals. I am also grateful to Mr. Daramola Olarinmoye for typing 
the manuscript, the entire staff of the Medical Illustration Centre, 
University of Ibadan, for tracing and photographing the graphs, and
friends for their concern and encouragement.
This work has been financially supported by the Population 
Council , New York and this is hereby most gratefully acknowledged.
XI
Certification By Supervisor
This is to certify that the work recorded in this 
thesis was wholly carried out by Dr. 0. Adeyemo
under thea  supervision of Dr. Everett Heath.
Supervisor
Dr. ZV Heath, B.A., V.M.D., 
M.S., Ph.D.
Table of Contents
Page
Title page .. .. .0 . * i
Dedication .. .* ■ • * • • ii
Abstract .• .. .. • • • • iii.
List of Abbreviations • • vi
Acknowledgements ..' ix
Certification by Supervisor d r \ . xi
Table of Contents .. V • • • • xii
List of Figures • • • • xvi
List of Tables .. C y • • * • xviii
• •  * *
INTRODUCTION . . • 0 • • 1
LITERATURE REVIEW &
Adrenocortical Physiology .. .. « • • • 8
Plasma cortisol .. .• .. • 9 0 0 8
Control of secretion of cortisol 0 0 0 0 10
Effect of stress .. .• .• 0 9 0 0 12
Effect of exogenous ACTH .. 9 0 0 0 16
Role of cortisol in reproduction 0 9 0 0 17
Methods of assaying plasma cortisol 0 0 0 9 20
Estrous Cycles
Length of estrous cycle ,. .. 0 0 0 0 24
Duration of estrus .. .. 0 0 0 0 25
\
Xlll
Page
Time of onset of estrus . . •. .. .. 26
Estrual behaviour and ovulation .. .. 27
Effect of hign environmental temperature on estrous 
cycle .• t * •• •• •• 29
Relationship of photoperiod and estrous cycles 32
Relationship of nutrition and reproduction .. 33
Physiology of Body Temperatures .. •• 34
- Body temperature measurement .. 34
- Temperature regulation A. .. 35
- Heat*  tolerance ^ o  . 43
- Influence of shade on thermoregulation 48
- Climatic heat store'ss  factors .. 48
MATERIALS AND METHOD
Experimental animals .. .. .. 53
Climate of Ibadan .. ,. .. 54 
Experimental design .. .. .. 58 
Radioimmunoassay of bovine plasma cortisol 74
- Introduction .. .. .. .. 74
- Glassware and solutions .. .. 74
- Preparation of samples .. .. 78
~ The assay .. .. .. .. 78
- Calculations .. .. .. .. 80
xiv
Page
RESULTS AND DISCUSSIONS
I Physiological responses 
Results:
Respiratory rates .. 31
Rectal temperature .. 82
' " a S "
Shade seeking •. .. • dr ” 83
Discussion: .. . . 85
II Estrous cycles in heifers 
Results:
Pubertal age .» .o. . 100 
Estrual signs . .y .. loo
Time of onset o4f <estrus 104
Duration of estrus . . .. 105 
*
Ovulation .. .. . . 107 
Rhythmicity of estrous cycles 107 
Discussion: .. . . .. 110
Ill Plasma cortisol concentration during estrous 
cycles and different quarters of the year.
Results: .. .. .. .. .. 122
Discussion: .. .. .. .. .. 124
IV Diurnal and circadian changes in physiological 
responses and plasma cortisol concentration
Respiratory rate and rectal temperatures .. 133
Responses in heifers in the sun .. .. 133
Physiological responses in heifers under shade 135
Circadian rectal temperature and respiratory 
rate in the shade .. .o .. .. 137
Plasma cortisol „. •. .„ .- 137
Discussion: •. *. .„ .. .• 140
V Effect of exogenous adrenocorticotrophin\>n 
adrenocortical functions and estrous cycle
Results 149
Discussions .. . . . . 151
SUMMARY AND CONCLUSIONS ^  . 156
REFERENCES .. 214
•APPENDIX •• .. 248
• •  *  • •  •
Test of reliability of radioimmunoassay of 
cortisol •. .. .• .. 248
(See alsi t of Appendix Tables)
xvi
List of Figures Page
Figure 1: A German-Brown heifer .. .. 186
Figure 2: A Holstein-Friesian heifer .. • « 187
Figure 3: A White Fulani heifer .. •. • • 188
Figure 4: Percentage monthly weight changes: composite
of four heifers/breed .. - 189
Figure 5: Weather conditions of the University of 
Ibadan Campus from December 1975 to 
December 1976 .. .• .. 190
-
Figure 6: Mean diurnal environmental temperature and 
humidity during periods when physiological 
studies on heifers were conducted *. 191
Figure 7: Mean respiratory rates and rectal temperatures 
in heifers .. .. .. 192
Figure 8: Rectal temperature: Composite of 5 - 7 
cycles/breed .. .. •. 193
Figure 9: Shade seeking habit of heifers ,. 194
Figure 10: Panting Holstein heifer .• .. 195
Figure 11: Percent distribution of time of onset of 
strus .. .. .. .. .. 196
Figure 12: Percent distribution of duration of estrus 197
Figure 13: Percent distribution of estrous cycle
length .. .. .. .. .. 198
Figure 14: Plasma cortisol concentration during
estrous cycles: composite of 4 heifers/ 
breed (December - January) .. .. 199
Figure 15: Plasma cortisol concentration during estrous 
cycles: composite of 4 heifers/breed
(March - April) .. .. .. 200
xvii
?age
16 r Piasnia cortisol concentration during
estrous cycles: composite of 4 heifers/ 
breed (July - August). .. .. .. 201
12 i plasma .cortisol -concentration during estrous 
cycles: composite of 4 heifers/breed .
(November) .. .. .. •. ..
18: Mean plasma cortisol concentration in heifers 
during four periods of the year. .. .. 203
19: Diurnal Ohanges in rectal temperatures and 
respiratory rates in heifers (Unshaded) .. 204
20: Diurnal changes in rectal temperatures and 
respiratory rates in heifers (under shade) 205
21: Circadian changes in rectal temperature and 
respiration rates in heifers (under shade) 206
22: Diurnal plasma cortisol concentration in 
heifers . „ . . • .. 0 207
23: Diurnal plasma cortisol concentration in 
heifers .. *. . • .. * 208
24: Circadian plasma cortisol concentration: 
composite of three heifers/breed. .. ., 209
25: Plasma cortisol concentration after saline
and ACTH injections .. .. •» .. 210
26: Mean plasma cortisol concentration after
saline and ACTH injections: composite of six 
heifers .. .• ♦. .. .. 211
27: Standing-for-mounting estrual behaviour 212
28: Estrual sign (tail raising) 213
xviii
List of Tables
In Text: Page
Table I: Mean respiratory rates in heifers during
different periods of the year. .. .. 165
Table II: Mean percent change in respiratory rate at
15.00 from values at 07.00 hours. .. .. 166
Table III: Mean morning (07.00 hour) and afternoon4 ,
(07.00 hour) rectal temperatures, along 
with the standard deviations, in heifers 
during four quarters of the year. .. .. 167
Table IV: Mean age of commencement of estrous cycles
in Brown, Holstein and Fulani heifers. 168
Table V: Percentage distribution of time of onset r _
of estrus in heifers .. .. .. 169
Table VI: Duration of estrus 4ibn heifers through one
calendar year. .. .. .. ' .. 170
Table VII: Breed comparisons of the duration of estrus
in heifers. .. .. .. .. .. 171
Table VIII: Comparison of the duration of estrus in
heifers during the wet and dry seasons .. 171 
Table IX: Ovulation interval (in hours)... .. 172
Table X : Comparison of ovulation interval after the
end of estrus in heifers. .. .. .. 172
Table XI: Ovulation interval after the end of estrus in 
Brown, Holstein, and Fulani heifers: 
observations in the wet and dry seasons 
compared. .. .. .. .. .. 173
Table XII: The character of the frequency of estrous cycle
lengths in heifers. .. .. .. .. 174
Table XIII: Estrous cycle lengths in heifers through the wet 
and dry seasons. .. .. .. .. 175
Table XIV: Comparison of estrous cycle length in the
wet and dry seasons .. .. .. .. 176
xix
Page
Table XV: Comparison of the estrous cycle lengths 
in the Brown, Holstein and White Fulani 
heifers 177
Table XVI; Mean plasma cortisol concentration in heifers 
during different quarters of the year 178
Table XVII: Mean rectal temperature and respiratory rates 
in heifers kept outdoors in the sun through­
out the day time. . .  .. .. .. 179
Table XVIII: Diurnal rectal temperatures and respiratory 
rates of heifers in the shade .. .. 180
Table XIX: Circadian rectal temperature and respiratory 
rates in heifers in the shade .. .. 181
Table XX: Diurnal plasma cortisol concentration in 
heifers (Experiment 1) .. .. .. 182
Table XXI: Plasma cortisol concentration in heifers
separated from the usual group (Experiment 2) 183
Table XXII: Mean, with the standard error, diurnal plasma 
cortisol concentration in heifers 
(Experiment 3) .. .. .. .. 184
Table XXIII: Diurnal plasma cortisol, with the standard 
error, in heifers of the Brown, Holstein 
and Fulani breeds of cattle (Experiment 4)
In Appendix 
Table A 1: Assay of cortisol in increasing volumes of 
plasma .. .. «. .. «« • • 251
Table A 2: Recovery of cortisol in water in a single
clSS^y ♦ • m « * • • • • • 252
Table A 3: Recovery of cortisol in acqueous solutions in 
20 duplicate assays .. .. .. 253
XX
Page
Table A 4: ^plication of samples in the same assay .. 254
Table A 5: Duplication in two different assays .. 255
Table A 6: Test of acuracy of assay ., .. .. 256
Table A 7: World Health Organisation (W.H.O.) quality
control of radioimmunoassay .. .. 257
Table A 8: Standard curve of cortisol radiommunoassay 258
Table A 9: Summary of monthly weather observations for 
the University of Ibadan Campus from . 
December 1975 through December 1976 259
Table A 10: Mean haemoglobin concentration a2nvd packed 
cell volume during cool wet and dry hot 
seasons •• »• . « • • .« 260
Table All PCV (%) and Hb (g/lOQml): Cool wet and dry
hot seasons compared ,. .. .. 261
Table A 12: Mean respiratory rates (breaths/minute) of 
individual Brown, Holstein and Fulani 
heifers at 07.00 and 15.00 hours during 42 
consecutive days at different quarters of 
the year. .. .. .. .. .. 262
Table A 13: Analysis of variance of respiratory rates in
heifers of three breeds of cattle during four 
periods of the year. .. .. .. 263
Table A 14: Contribution to total variation that occurred 
in the respiratory rates .. .. .. 263
Table A 15: Mean rectal temperature (°F) of individual
Brown Holstein and Fulani heifers at 07.00
and 175.00 hours during 42 consecutive days at 
different periods of the year .. .. 264
Table A 16: Analysis of variance of rectal temperatures in 
heifers of three breeds of cattle during 
four different periods of the year. .. 265
xxi
Page
Table A 17: Contribution to total variations that occurred
in rectal temperatures . , .  .. 265
Table A 18: Analysis of variance of shade seeking scores
in heifers of Brown and Holstein oattle grazed 
in the sun. .. .. .. .. .. 266
Table A 19: Mean percentage scores of shade seeking in the 
heifers during different periods of the year.- 
observations were taken on 10 randomly chosen 
days of each quarter. .. .. .. 266
Table A 20 : Average scores of estrous intensity in heifers, 267
Table A 21: Distribution of the time of comm
<enpcement of 
estrus through the 24-hour day in heifers: 
observations were made over one calendar 
year• •« «• •« •* •• i■ 268
Table A 22: Analysis of variance of time of onset of estrus
in heifers through the year. .. .. 269
Table A 23: Duration of estrus in Brcown Holstein and
Fulani haifers through the year. 270
Table A 24: Interval of ovulation from end and onset of
estrus in Brown, Holstein and Fulani heifers 271
Table A 25: Mean plasma cortisol concentration in indivi­
dual heifers (observations made on alternate 
days), •• ,, «• * * .« 2 7:
Table A 26 Mean plasma cortisol concentration in individual 
' heifers. .. .. .. 273
Table A 27: Analysis of variance of plasma cortisol levels 
in heifers: levels at diestrus, estrus and 
the mean during four quarters were compared 274
Table A 28a: Analysis of variance of plasma cortisol concen­
tration in Brown, Holstein and Fulani heifers 
through four different quarters of the year. 275
Table 1\ 28b: Contribution to total variation 275
xxii
Page
Table A 29: Rectal temperature and respiratory responses
of heifers in the sun. .. .. .. 276
Table A 30: Analysis of variance of respiratory rates
of heifers in the sun. .. .. .. 277
Table A 31s Analysis of variance of rectal temperature*
of heifers in the sun. .. .. .. 278
Table A 32: Correlations between rectal temperaturey
respiratory rate and environmental temperature
in the sun 279
Table A 33: Analysis of variance of readings of circadian 
rectal temperature of heifers in the shade. 280
Table A 34: Analysis of variance of respisratory rates of 
heifers kept in the shade and in the sun. 281
Table A 35: Analysis of variance of values of rectal
temperatures in heifers in the shade and in 
the sun. .. •• •• •• •• 282
Table A 36: Plasma cortisol concentration and rectal 
temperatures of heifers kept in the sun ' 
throughout the day (Experiment 1). .. 283
Table A 37: Diurnal plasma cortisol concentration in
heifers (Experiment 3) .. .. .. 284
Table A 38: Analysis of variance of diurnal plasma cortisol 
concentration in heifer (Experiment 1). .. 285
Table A 39: Correlation between plasma cortisol and rectal 
temperatures of heifers kept in the sun 
(Experiment 1) .. .. .. .. 286
Table A 40: Analysis of variance of diurnal plasma 
cortisol concentration in heifers 
(Experiment 3). .. .. .. .. 287
Table A 41: Circadian plasma cortisol concentration in 
heifers (Experiment 4) 288
xxiii
Table & 42: Analysis of variance of circadian plasma 
cortisol in heifers (Experiment 4) ..
Table A 43: Mean rectal temperatures of non^lactating
pregnant cows and non-lactating non-pregnant 
nulliparous heifers in the sun, unshaded and 
shaded» •• «• •• «• • •
Table A 44: Plasma cortisol concentration at different
time intervals in heifers injected with 
saline and ACTH (200 IU). .. ..
Table A 45: Analysis of variance of plasma cortisol
concentration in heifers injected with saline 
and ACTH. .. .. .. ..
Table A 46: Analysis of variance of plasvma cortisol values 
in heifers injected with ACTH. .. ..
Table A 47: Analysis of variance of plasma cortisol values 
in heifers injected with saline .. ..
v X )
1
INTRODUCTION
The shortage of animal protein is a nutritional problem among
♦ . • .
the human population in most developing tropical countries including 
Nigeria. Development plans call for increased production of milk as 
well as beef. About thirty percent of the beef supply to Nigerian 
population has been from neighbouring countries of Chad and Niger
as live animals, and recently from more distan<t tcountries in 
South America, Europe and Australia as frozen meat (David-West 1977). 
The supply of milk is solely through importations from Europe and 
America. The national cattle herd of Nigeria (about 8.5 million) 
is largely in the hands of nomadic landless traditional grazers<
The level of productivity of these animals with respect to beef is 
far below market demand, and with respect to milk, is so low as to be 
unnoticed by the population.
To improve upon the quantity and quality of locally supplied 
beef, ranches stocked with African beef breeds of cattle have been
establishe<ds art  Mokwa, Upper Ogun, Ado~Ekiti, v:A koko, O^budu, Bauchi and 
a few other locations in Nigeria. Nomadic herdsmen have also been 
encouraged to settle in different states.
The increasing demand for high quality animal products has 
also underlined the urgent need for providing animals of enhanced 
efficiency in Nigeria (Oyenuga and Olubajo 1966). As in many hot 
countries of the world, improvement has been sought by the introduction
2
of animals from the temperate zones for the establishment of dairy 
units and for upgrading the local breeds through cross breeding. 
Other objectives have been to increase the earning capacity of 
fanners and promote national self-sufficiency in food supply.
There now exist small dairy units stocked with exotic breeds and, 
in some cases, the crosses with zebu breeds at Agege, Ibadan, Vom,
Obudu and other government farms.
Generally the performance of European cattle introduced to the 
tropics and sub-tropics have been poor. This has been blamed on 
both direct and indirect climatic factors. The indirect climatic
factors include irregular feed supply, inadequate water supply
and disease (Bonsma 1949; John 1975). The combination of the
direct factors such as environmental temperature, solar radiation, 
relative humidity, precipitation and wind movement is believed to 
affect the body heat balance of cattle (Lee and Phillip 1948; Bonsma 
and Louw 1963? Ojo 1971) . Responses are therefore stimulated in the 
animal and these include changes in reproduction and in endocrine 
and physiological functions (Gaalaas 1945; Rhcad 1936; Stott and 
Thomas 1972? Thatcher 1974).
In response to exposure to hot environment, cattle tend to 
increase body heat loss by theix respiratory and sweating activities. 
Marked elevation of body temperature arvd respiratory rate are 
considered indicative of heat stress in cattle (Rhoad 1940?
3
Findlay 1954? McDowell et al 1955; Wolff and Monty, Jr. 1974).
Rectal temperature changes form the basis of tolerance
tests and have been used to determine adaptability of different 
breeds of cattle to hot environment (Berman 1968; Bianca 1962). 
Cattle also exhibit behavioural responses to exposure to heat among 
which are panting and shade seeking (Hafez 1964) * ^ t  is, therefore 
desirable to determine the adaptability of both exotic and local 
breeds of cattle in a tropical environment by observing their 
physiological and behavioural responses under different weather
conditions.
The maintenance of reproductive capacity is an essential 
aspect of cattle production. Bonsma and Louw (1963) stressed the 
need to study the physiology of reproduction of exotic breeds of 
cattle in a tropical region "because of the great economic importance 
of fertility, adversely affected by hot environment in determining 
the turnover of any animal production". Many literature reviews
have also stressed the deliterious effect of tropical and sub­
tropical environment on reproductive performance of European breeds 
of cattle (Ulberg 1958; Bianca 1965; Vincent 1972? Thompson 1973; 
Moberg 1976; Waites 1976).
Seasonal depression in bovine fertility in a subtropical , • 
region has been attributed to heat stress affecting the cow (Stott 
1961). Heat is, however, also known to depress reproductive
4
efficiency of bulls (Johnston et al 1963). The two periods of 
the bovine reproductive cycle vulnerable to heat stress are the 
periods of estrus to ovulation and of implantation and early 
embryogenesis (Plasse et al 1970; Stott 1972; Moberg 1976? Stott 
and William 1962). Various reports have shown that heat stress can 
alter the estrous cycle of Bos taurus (Bond & McDowell 1972? Gangway 
et al 1965? Hall et al 1959? Labhsetwar et al 1963? Stott and 
Williams 1962)* Despite the relatively more uniform daylight .and
ambient temperatures throughout the year in areas near the equator, 
zebu and some other African types of cattle have shown seasonal pattern 
in breeding (Wilson 1946? Steinbach & Balogun 1971? Jochle 1971).
The reproductive physiooloJgyT of temperate-evolved cattle 
introduced into tropical Nigeria has not been well studied and much 
of the knowledge about them is based on observations made in other 
parts of the worjjt*^ Detailed study of the reproductive cycles of
the local zebu breeds of cattle is also still lacking? and as 
Jochle (1972) pointed out, most literature reviews overlook this 
aspect in zebu cattle, A study of the estrous cycles of both 
local and exotic breeds of cattle may elucidate how their breeding 
is influenced by environmental conditions of the hot climate.
Adrenocortical function is increased in cattle under acute 
thermal stress (Stott & Robinson 1970? Christison & Johnson 1972? 
Alvarez & Johnson 1973), It however decreases under prolonged heat 
exposure (Christison & Johnson 1972, Rhynes & Ewing 1973). Severe
5
seasonal heat exposure is also known to depress cortisol secretion 
in cattle (Stott and Wiersma 1971). Abilay, Johnson and Madan 
(1975) suggested this latter change to be a thermoregulatory 
mechanism to reduce body heat load, since hydrocortisone is thermo­
genic (Yousef & Johnson 1967). Increased circulating cortisol levels 
would be undesirable in a hot environment not only because it can 
be associated with increased metabolic heat, but< alPso because of the
catabolic effects of glucocorticoids by causing increased mobilisa­
tion of tissue amino-acids for gluconeogenesis and increased blood 
glucose (Ray 1968? Burke 1973). Most of the studies on adreno­
cortical functions in cattle have been done in the climatic laboratory 
with the result that little is known regarding the influences of 
natural weather.
In 1971, Ojo reported a study of heat balance in Jersey and 
Shortorn using energy budget on the skin surface at different 
locations in Nigeria at different periods of the year. He concluded 
that the area around Ibadan is the next most suitable place after 
the Jos Plateau area in Nigeria for the establishment of temperate- 
evolved cattle.
Amakiri (1974), in a study of the skin of both exotic and 
local breeds of cattle in the Ibadan area, found that the Friesian 
Cattle had developed sweat gland characteristics suitable to a hot 
environment. Informations on the physiological and hormonal 
responses of these animals were, however, lacking.
6
Generally, equatorial zone (sea level) is believed to present 
severe limitations to the performance of temperate-evolved cattle 
(Johnson 1975). Rollinson (1962) has summarised the general 
agreement that temperate-evolved cattle are most suited to
geographical areas with temperatures ranging between 30 and 65 F,
High altitudes in the equatorial *one and pi th temperatures
ranging between 70 and 75 F might be tolerable. Zebu cattle are most
suited to temperature ranges of 50 F to By these standards,
X
Ibadan, the area of the present study, is suitable for zebu cattle 
but not for temperate-evolved cattle. How the latter type of cattle, 
translated to the tropics, adapts to a potentially unsuitable 
climate would be of economic and scientific interest.
The objectives of the present study were:
(1) to characterise estrous cycles in temperate-evolved and zebu 
heifers with regard to the length of the cycles, time of onset of 
estrus, duration of estrus and ovulation time, in a hot/humid
subequatorial climate,
(2) to investigate the relationship of adrenocortical functions 
and related physiological functions (respiratory rate and rectal 
temperature) with the phases of estrous cycles at different quarters 
of the year,
(3) to investigate the variations in adrenocortical functions and 
the physiological responses during the diurnal and/or circadian 
period in the shaded and unshaded environments,
7
and (4) to examine adrenocortical responsiveness to exogenous 
adrenocorticotrophic hormone (ACTH), as well as the effect of the 
latter on normal estrous cycles.
8
LITERATURE REVIEW
Adrenocortical physiology
Plasma cortisol
Cortisol and corticosterone have been identified as the 
principal corticosteroids in bovine plasma (Estergreen and 
Venkataseshu 1967). Of these two glucocorticoids, cortisol is both 
qualitatively and quantitatively the more important (Estergreen and 
Venkataseshu 1967; Rhynes and Ewing 1973; Venkataseshu and Estergreen 
1970). The ratio of cortisol to corticosterone in adrenal effluent 
is 5:1 (Whipp et al 1967). In jugular blood, the ratio has been 
found to be 2.4:1 and 24:1 by Venkataseshu and Estergreen (1970) 
and Swanson et al (1972) respectively.
Other important adrenal cortical hormones, aldosterone (mineral^- 
corticoid) and adrogens, have been identified in cattle as well 
as limited quantities of other steroids with sex hormone activity 
whose roles are not fully known (Gorski et al. 1958, Meiampy et al.
1954; McDonald d Turner and Bagnara 1971)
The structure, biosynthesis and metabolism of adrenal
corticoids have been well studied (Gray et al. 1961', Loraine and 
Bell 1966,* Turner and Bagnara 1971). Cortisol, like other adrenal
9
corticoids, is synthesised in the cortex of the gland from 
cholesterol;A~5 pregnenolone and progesterone are important in 
the series of intermediaries.
Ninety-nine percent of circulatory cortisol is metabolised 
in the liver and less than one percent appears in urine unchanged 
(Gray et. al 1961). The carbonyl group at position 3 is utilised 
in conjugation to glucoronic acid, or possibly sulphoric acid. The 
renal clearance of reduced and conjugated metabolites is so rapid
that the unmetabolised hormone constitues the preponderant part 
of plasma corticoids (Migeon et. al 1956).
Eighty percent of circulatory cortisol is bound in plasma 
to the cortisol binding globulin (CBG), transcortin; and the 
remainder is loosely bound to albumin (Sandberg and Slaunvhite, Jr. 
1959). The level of plasma cortisol is dependent on tbe binding 
capacity of transcortin in a given species (Linder 196U). High levels 
occur in man and rat; and low levels occur in sheep and cattle. The 
binding affinity of transcortin is reduced at increasing environmental 
temperatures (U-37°C) (Linder 196U).
The amoving of cortisol bound in blood of man is increased by 
estrogen (Sandberg and Slaunwhite Jr. 1959). Estrogen, however, 
has no such effect in the ewe. There is evidence to indicate that is 
is the unbound (free) fraction of cortisol which is physiologically 
active (Sandberg and Slaunwhite 1959 ; Slaunwhite, Jr. et. al 
1962). An increase in the circulating level of cortisol therefore
10
does not necessarily imply an increased availability of biologically 
active hormone. For example, in man, the elevated levels during 
pregnancy is due to an increase in the concentration of plasma 
transcortin and the bound fraction of cortisol whereas the amount 
of free cortisol is not markedly changed (Booth et al. 1961).
Control of secretion of cortisol
The rate of biosynthesis and secret:iioon of adrenal steroids is
controlled by adrenocorticotropic hormonesO (ACTH), an anterior
pituitary hormone (Fevold 1, 967; Saltnenpe>r a• 'and Kahri 1976). The 
release of ACTH is also under the control of corticotrophin- 
releasing factor (CRF), a neural hormone from nuclei in the median
eminence of the hypothalamus (Hiroshige et al. 1969). CRF is 
passed via the hypothalamic-hypophyseal portal system. The secretion 
of CRF, in turn, is affected by neural impulses from higher centres.
It is believed that impulses from the reticular formation inhibit 
CRF while impulses from other areas resulting from trauma, fever 
or noise, for example, decrease reticular inhibition (James and 
Landon 1976).
Rising levels of cortisol suppress the production of ACTH in 
the adenohypophysis and CRF production in the median eminence of 
the hypothalamus (Brodish and Lang 1962; Chowers et al. 1967).
This is referred to as the “long feedback loop.1* ACTH also has a 
direct inhibitory effect on the production of CRF in the median 
eminence, constituting the "short feedback loop."
11
Because of these interrelationships, rhythmical changes in 
the release of CRF have been associated with corresponding variations 
in the release of adrenocorticoids. For example, synchronous peaks 
of ACTH and corticosteroids have been demonstrated in man (Krieger 
et al. 1971). There is also evidence that the daily rhythm of CRF 
is associated with variations in plasma corticosteroid concentration 
in rats (Takebe et al. 1970, Seiden and Brodish 1972). Circadian 
rhythm in the plasma levels of cortisol has been described in man,
with peaks occurring before the period or awakening and decreasing 
gradually subsequently through the 24-hour period (Perkoff et al. 
1959). A similar rhythm has been described in rats, with the peak 
occurring in the evening when these animals become active {Guillemin 
et al. 1959). Initial animal and human studies deliniating 
corticosteroid circadian periodicity were based on a sampling 
frequency of every 4 - 6  hours over 24-hour period with resultant
curves describing a smooth rise and fall over this time period
/
(Migeon et al. 1956). Krieger et al. (1969) and Heilman et al.
(1970) demonstrated episodic peaks in plasma corticosteroids (and 
ACTH) throughout the day by sampling man more frequently at every 
30 and 20 minutes respectively.
Evidence for circadian rhythmicity in circulatory plasma 
corticosteroid in cattle was first given by MacAdam and Eberhart 
(1972) and Wagner and Oxenreider (1972) but was contradicted in 
other reports (Paape et al. 1973; Hudson et al. 1975).
12
Effect of stress
Studies in psychrometric chambers have shown that acute 'H-stti'vial 
exposure of cattle caused increases in their adrenocortical 
functions. Under this condition, levels of plasma cortisol (or 
glucocorticoid) rose (Stott and Robinson 1970? Christison and 
Johnson 1972? Alvarez and Johnson 1973? Abilay, Mitra and Johnson 
1975) . The turnover rate of plasma glucocorticoid or cortisol in
particular also rose (Stott and Robinson 1970; Christison and
Johnson 1972). Such elevations in plasma cortisol level h&ve been 
found to be shortlived, lasting only 1 hour and declining to original 
basal levels in 4 - 5 hours (Alvarez and Johnson 1973). Impulses
set up at the thermoreceptorss iyn the skin by acute thermal stimuli 
are capable of stimulating increased ACTH release and a corresponding
adrenocortical secretion (Chowers et al. 1966).
Adrenocortical functions in cattle under chronic thermal 
stress is dissimilar to that under acute thermal Stress, plasma
cortisol concentration has been found to be reduced in cows exposed 
chronically to a warm environment of 29°C for 9 consecutive weeks 
(Bergman and Johnson 1963). In addition to the reduction in plasma 
levels, the turnover rate of cortisol was found to be reduced in 
cattle exposed to 35°C (RH 50%) for 7 - 1 0  weeks .(Christison and 
Johnson 1972). Similarly, bulls exposed chronically to constant 
environmental temperature of 35°C had low plasma glucocorticoid
13
levels (Rhynes and Ewing (1973). Heat stress affects plasma cortisol
level more than corticosterone levels, the ratio at 21 o C and 35 oC being 
6:1 and 4:1 respectively (Rhynes and Ewing 1973).
Yousef and Johnson (1967) found that administration of 
hydrocortisone acetate (1.25g/cow intravenously) caused heat production 
in cows to increase. The decline in plasma levels“of glucocorticoids
which occurs during chronic exposure to a hot environment has therefore
been suggested to be a regulatory protectiv<e mechanism to reduce the
animal's metabolic heat production.
The mechanism by which heat causes a reduction in adrenal 
corticoid secretion in cattle isrnot known. Yates et al. (1961) 
suggested that the threshold of the adrenal cortex may shift during 
prolonged heat exposure, so that even when plasma ACTH level is high, 
little glucocorticoid is produced. Marple et al. (1972) working on 
gilts also supported this suggestion. Abilay, Johnson and Madan 
(1975) proposed that the 17-hydroxylating enzyme responsible for the 
synthesis of cortisol from progesterone may be inhibited by chronic 
exposure to heat. This may therefore be responsible for observed 
increases in adrenal content and circulating level of progesterone in 
cattle chronically exposed to heat (Wiersma and Stott 1969; Abilay, 
Johnson and Madan 1975).
14
As regards the effect of natural weather, the excretion of 
17-ketogenic steroids in sheep has been found to be reduced in summer 
(Robinson and Morris 1960). It has been reported that levels 
obtained during lactation remain stable and have no association with 
season or mean environmental temperature (Koprowski and Tucker 1973; 
Shayanfar et al. 1975). Contrarily, Lee et. al (1976) reported 
lowered plasma glucocorticoid levels in dairy cattle during hot 
weather. This supports an earlier observation that summer heat 
depressed adrenocortical function in cattle (Stott and Wiersma 1971).
Adrenocortical function has not been exammii:ned in either local or
imported temperate-evolved cattle in the tropical Nigerian environment.
Christison and Johnson (1972) suggested that the initial brief 
increase in adrenocortical response in cattle exposed to heat was a 
result of stress reaction not specific to heat exposure. Accordingly, 
the effect of many other stressful conditions have been observed by 
various workers. Elevated corticoid levels were obtained in “untrained-' 
sheep bled by venipuncture (Linder 1964; Basset and Hinks 1969). Stress 
to the method of bleeding may be responsible for the large variations 
obtained in bovine plasma corticoid (Venkataseshu & Estergreen 1970; 
Garverick et al. 1971; Spraque 1969). Other causes may be the removal 
of large quantities of blood and the assay method (Venkataseshu and 
Estergreen 1970; Robertson and Mixner 1956; Paterson 1957). The time 
interval for collecting samples could also affect the plasma level of
15
cortisol. Shaw and Nichols (1963) found no elevation of 17-hydroxy- 
corticosteroid in cows sampled at 30 to 6C-rainute intervals, but 
sampling at intervals of 10 minutes caused an elevation within 30 to 
110 minutes which could be further increased by ACTE! administration.
Animals, however, can get used to handling and blood sampling 
as was demonstrated in trained, untrained and even herded sheep
(Bassett and Hinks 1969; Linder 1964; McNarthy anda Thurley 1973). It
has also been possible to obtain physiological levels of plasma
s y
glucocorticoid in trained heifers (Gimenez et al. 1974). Similarly 
to the report on sheep quoted above, Rhymes and Ewing (1973) observed 
that steers were apprehensive on first handling and confinement and 
their plasma cortisol level was high,- the level however dropped by aboua 
40% when (after 5 weeks) the heifers got used to the procedure and 
acclimatized.
‘'Training'- or adaptation by the animal to handling or
experimental procedure is suggested to be controlled by the central 
nervous system (McNarthy and Thurley 1973). Studies in rat also show 
that adaptation to stress is associated with normalising of the 
activity of the tropic cells of adenohypophysis which had been hyper­
active initially (Pollar et al 1976).
16
Effect of exogenous ACTH
Stress-like response of the adrenal cortex has fooeo. elicited 
on administration of exogenous ACTH to cattle with pronounced 
secretions of adrenal glucocorticoids (Shaw and Nichols 1963; 
Venkataseshu and Estergreen 1970,-Gwazdauskas et al 1972; Paape et al* 
1973; Paape et al. 1974; Shayanfar et al. 1975; Satterlee et al. 1977)i 
Plasma corticosterone values did not change significantly after ACTH
administration compared to the changes, in plasma coDrtisol concentration
(Venkataseshu and Estergreen 1970)
Peak corticosteroid response occurred 60 minutes post-ACTFI 
treatment (Venkataseshu and Estergreen 1970; Wagner et al 1972).
These reports also show that plasma corticosteroid levels returned to 
normal within 24 hours post-ACTH treatment* Accumulation of adreno­
cortical responses to method of blood collection and ACTH administration 
has been demonstrated in calves (Shaw and Nichols 1963).
A group of workers found no differences in either magnitude or 
duration of plasma corticosteroid responses of lactating cows to 
ACTH (200IU) among controlled temperature periods of 21°C, 65% RH 
and fluctuating 12-hour cycles of 32°C, 65% RH during the day and 21°C, 
65% RH at night (Paape et al, 1973). In another study in the climatic 
laboratory in which more prolonged acclimatisation periods than in 
the former report were allowed, heifers under cold (5°C, 30% RH), 
thermoneutral (18°C, 50% RH) and hot (35°C, 80% RH) conditions showed 
similar plasma glucocorticoid responses to ACTH treatment (Satterlee
et al. 1977).
17
These results did not agree with the report of Shayanfar et al 
(1975) in the field that lower adrenal responsiveness to ACTH may 
exist in lactating cows exposed to high environmental temperatures 
ranging from 21.1 to 26.9°C than in cows exposed to low environmental 
temperatures (6.4 to 21°C). It is not known what the adrenocortical
responsiveness to exogenous ACTH in heifers raised under natural hot/ 
humid climatic condition would be like.
Role of cortisol in reproduction
The direct role of glucocorticoid^^! reproductive activity 
and with particular regard to different stages of the estrous cycle
of cattle, has not been fully established. Plasma levels of cortisol 
fluctuate throughout the menstrual cycle of women (Abraham et al 1972). 
Many reports also show that plasma levels of glucocorticoid vary during 
estrous cycle of cattle with no significant differences between the
days (Sprague 1969; Randel et al. 1971; Garverick et al., 1971)
Other reports have shown that despite the fluctuations, a significant 
elevation on the day of estrus or around estrus was noticeable 
(Shaw et al, 1960; Arije et al, 1971; Miller and Alliston 1974; 
Gimenez et al., 1974). Contrarily, the result of Abilay, Johnson and 
Madan (1975) showed that levels on the day of estrus were lower than
other days of estrous cycles in heifers in the climatic laboratory.
18
Either ACTH or glucocorticoid administration has delayed onset
r><v. v.
of estrus in the sow (Liptrap 1970)• ACTH administration has also 
delayed onset of estrus in mice (Christian 1964). Administration of 
glucocorticoid of stress-induced increases in the hormone had 
increased embryonic mortality in rats, rabbits and sheep (Euiker and 
Riegle 1973? Kendall and Liggins 1972? Howarth and Hawk 1968).
Hormone of adrenal-pituitary axis can, therefore, affect those aspects
of reproduction which are vulnerable to str
In rats, administration of synthetic #glucocorticoid, dexamethasone, 
has altered estrous cycle length, blocked ovulatory surge of luteinising 
hormone (LH), apparently by inhibiting the synthesis and release of 
pituitary LH (Baldwin and Sawyer 1974). A similar treatment has also 
inhibited pregnant mare serum-induced ovulation.-in rat (Hagino et al.
1969). It has therefore been suggested that stress prior to ovulation in > 
may be capable of blocking ovulatory release of LH and thereby change
the natural temporal pattern of estrual behaviour and the time of 
ovulation, which can cause a wrong timing of breeding in cattle and, 
therefore, adversely affect conception rate (Moberg 1976).
Administration of dexamethasone to cows at the beginning of 
estrous cycles during summer in Arizona did not improve fertility* It
was therefore, suggested that low circulating plasma cortisoi level
under hot condi•t'I*i ons may.. not be a cause o f infertility (Monty Jr. and 
Wolff 1974).
19
Only very few attempts have been made to investigate the 
influence of environmental conditions on the association between plasma 
cortisol and different stages qf estrous cycles. In the psychrometric 
chamber, Abilay, Johnson and Madan (1975) investigated the effect of 
constant high temperature (35.5°C) while Miller and Alliston (1974) 
utilised programmed circadian environmental temperatures varying between 
21°C by night and 34°C by day. Ther^*«al treatment caused a depression
in the levels of circulating cortisol at all stages of the estrous 
cycle except on the day of estrus, that is, the first day of exposure 
to heat in the former study, or except during the first week of exposure 
including the day of estrus in the latter study. Reports are still 
lacking on the influence of changing seasons on the association between 
plasma cortisol and the different stages of estrous cycles in cattle 
in the field.
In sheep, parturition is associated with increased fetal adrenal 
secretion of corticoids near the end of gestation (Liggins 1968;
Basset and Thorburn 1969). Elevated plasma glucocorticoid 1-4 days 
prepartum has been demonstrated in cows (Adams and Wagner 1970). The 
elevation might occur 0-15 days prepartum (Heitzman et al. 1970). 
Parturition has been induced in cattle and sheep by administration of 
synthetic corticoid (Adams and Wagner 1970? Liggins 1969; Lauderdale 
1972). It has been suggested that the abrupt rise in plasma gluco­
corticoid near term may cause a decline in corpus luteal (CL) function 
and thus initiate parturition (Adams and Wagner, 1970). This suggestion
20
is supported by the report of Brunner et. al (1969) that exogenous 
ACTH administered on days 2 through 8 of estrous cycle in cycling 
heifers suppressed corpus luteal development during the period of 
treatment. The effect of this treatment is most probably due to 
elevated endogenous plasma glucocorticoid.
Adrenocortical suppression with betamethasone has resulted in 
prolonged estrous cycle length (Kanchev et. al 1976). Although these 
reports show that the CL of normal estrous cycle of cattle may be 
influenced by glucocorticoids, exogenous glucocorticoid administered 
to heifers from day 10 of estrous cycle could not produce luteolysis 
(Gimenez et. al 197*0. These last quoted workers therefore suggested 
that the luteolytic effect of glucocorticoid at the end of pregnancy 
is probably aided by the presence of some other factors present at 
that time in blood .-.but absent during normal estrous cycles. It is 
yet to be investigated whether increasing the levels of endogenous 
glucocorticoid by administering ACTH from midcycle stage, and later, 
can initiate the luteolytic process.
Methods of assaying plasma cortisol
Various methods have been used to quantitate plasma levels of 
corticoids (Loraine and Bell 1966; Sandberg and Slaunvhite Jr. 1975).
21
Assay techniques based on biological activities are unsatisfactory from 
the quantitative standpoint, and have given little information regarding 
the compound being measured (Vogt. 19^3; Paschkis et. al 1950). Chemical 
methods of colorimetry lack specificity (Nelson and Samuels 1952; 
Robertson and Mixner 1956). The physico-chemical methods including
double-isotope labelling, though
initial purification of extracts (Frazer and James 1968). Also, the 
fluorometric technique developed by Mattingly (1962), though requiring 
smaller plasma volume and faster than colorimetric procedures suffers 
the disadvantage of interference by other fluorescing contaminants, 
and, therefore, requires scrupulous cleaning of glassware (Sandberg and
In the nineteen sixties assay of cortisol which depends upon the 
principle of displacement analysis involving the use of very small 
volumes of plasma were.' developed. These have the advantages of 
rapidity, simplicity and specificity. Large numbers of samples can 
also be treated at the same time. These methods have employed iodine 
125- or tritium-labelled cortisol as- a binding agent. The competitive 
protein bidning (CPB) method involves the use of transcortin as the
22
binding agent- (Murphy 1967). The bidding agent in radioimmunoassay 
(RIA) is an antibody raised against cortisol (Abraham et. al 1972; 
Parmer and Pierde 197*0. Because of the specificity of the antibody, 
the problem of interference due to other hormones or other compounds in 
plasma is considerably reduced, thus improving the sensitivity of the 
assay when RIA is employed (Abraham et. al 1972).
The technical details of RIA and the preparation of antibodies 
have been veil studied (Abraham 197**; Heins 197**; Nieschlag and
Wickings 1975). The principle may be describedo as competition between 
labelled and unlabelled antigen (hormone) for binding sites on the 
common antibody resultihg in the formation of labelled antigen-antibody 
and unlabelled antigen-antibody complexes. After the separation of 
the bound and free fractions, the concentration in the unknown (sample) 
is obtained by a comparison of its inhibition of binding of labelled 
antigen to antibody with* the inhibition produced by a set of known 
standards introTducjFed 'into the system.Various levels of basal plasma cortisol in cattlfe have been 
reported, depending on the method used. Saba (196**) using a method 
of soda fluorescence on paper ehromatography obtained a cortisol concentra­
tion of 0.5 ug/100 ml in bovine plasma. Some other workers using the
23
chemical method to determine AT-hydroxyoorticosteroida in "bovine plasma
r
obtained a range of 1.2 to 11.9 ug/100 ml (Shaw et. al I960; Robertson 
and Mixner 1956; Shaw and Nichols 1963). Using the competitive protein
binding ICPB) method basal lewels of plasma cortisol ranging, between 
1-10 ng/ml had been obtained in heifers and cows (Whipp and Lyon 1970; 
Swanson et. al 1972; Gimenez et. al 197**; Shayanfar et. al 1975;
Sat ter lee 1977; Gsrverick, 1971). Lower levels occur in cows than in 
calves (Whipp and Lyon 1970; Saba 196U). Using the RIA, Dobson and 
Kanchev (1977) found a level of 3.5-10 ng/ml in the plasma of heifers.
From evidences showing a normal relative high proportion of cortisol 
to the other glucocorticoids in bovine plasma including after ACTH 
or during actute thermal treatment, it is obvious that results from 
assaying cortisol alone in bovine blood would produce the same information 
about adrenocortical function as assaying total glucocorticoid. This 
observation was also made by Wagner and Oxenreider tl972)» Venkataseshu and 
Estergreen (1970) and Swanson et. al (1972).
24
Estrous Cycle
The average age of puberty in Bob taurus has been found to be 
between 6 - 1 5  months (Hammond, 1927) . Studies in India indicated 
that pubertal age of the Bos indicus population was between 33-47 
months (Amble et. al. 1953; Johari and Talapatra, 1957). Jochle 
(1971) observed that 28.4% of purebred Brahmans (American zebu) in
Mexico had first conceptions between the ages of 15 and 24 months 
while 44.6% conceived between 25 and 30 months. The average age of
puberty in Brahman heifers in a subtropical climaOtey was found to be 
19.4 months with a range of 14 to 24 months (Piasse, Warnick and Koaer 
1968). Reynolds et. al. (1963) found that Bos indicus reached pubertal
age later than Bos taurus and cross:
Length of estrous cycle
In Bos taurus, average es&trous cycle lengths varying between 
20 and 30 days have been recorded by several workers (Champman and
Casida, 1937); Olds and Seath, 1951; Trimberger, 1956; Hall et al 1959)• 
The cycle is reported to be slightly longer in the cow than in the 
heifers, the average in days being 21.28 and 20.23 days respectively 
(Thibault and Lavesseur, 1975). Rollinson (1962) indicated that 2.2 ~ 
6.8% of estrous cycles could fall below 18 days and about 13%. above 
24 days. About 16% of the cycles have been found to fall above 18 - 24 
days in Bos taurus cows (Asdell, et al 1949).
25
Generally the reports on estrous cycle length in zebu cattle are 
few and inconsistent. An average estrous cycle length of 22 and 23 
days have been reported in Bos taurus x Bos indicus and purebred Bos 
indicus cattle respectively (Anderson 1944). Rakha et al (1970) 
recorded average estrous cycle lengths of 'between 21 - 24 days in 
zebu and African types of cattle in Central Africa. Their result 
was similar to some previous reports in this respejce tt  (AAnncd erson, 1936,°
Clamohoy, 1952; Nazareno, 1954). The average in Srahman heifers was
found to be 28.8 days, with a standard deviation of 27.7 days, and a 
significant difference between heifers (Plasse et al 1970). Quinlan 
and Roux (1936) also reported similarly long estrous cycles in 
Africander X Sussex cattle.
Duration of estrus
Widely varied values have been reported for the duration of 
estrus in cattle. A range of 6 - 30 with a mean of 17 hours had been 
recorded in Bos taurus, being longer in the cow than in the heifer 
with an average of 19.3 and 16.1 hours respectively (Hammond 1927).
Values varying between 4 - 4 8  hours with means from 12.5 to 17 hours 
have been reported by several other workers (Brewster and Cole, 1941; 
Asdel, 1946; Hansel and Triraberger, 1952; Hough et al 1955; Trimberger 
and Hansel 1955; Ivankov, 1956; Gersimova, 1940; Esslemont and Bryant 
1976). Wiltbank et. al. (1957) reported a mean length of estrous of 
21.1 hours in beef breeds of Bos taurus.
Relatively short estrous periods have been recorded in Bos indicus 
by several workers, and have been believed to be the cause of low
26
reproductive performance in this species. Anderson (1936) reported 
an average length of 1 hour and 20 minutes for 74 estrous periods 
in zebu cattle. Again in 1944, Anderson reported an average of 4.8 
hours in zebu, and 7.4 hours in Bos taurus X Zebu cross, with a 
standard deviation of 2.2 and 2.4 respectively. The mean duration 
of estrus in Brahman heifers has been found to be 6.7 hours (Plasse
et al 1970). Contrary to these reports, estrus lasti ng between 13.4 
and 24 hours have been observed in Zebu cattle by other workers 
(Rollinson, 1955 ;V illacort.na  t1n960). In the Central Africa, Rakha et
al, 1970 recorded a mean of 16.3, 17.4 and 14.8 hours with standard 
deviations of 1.08, 1.18, and 0.53 respectively in Angoni, Barotse 
and Boran, all African and Zebu types of cattle; their heifers also 
exhibited longer estrus than the cows (Rakha and Igboeli, 1971). Their 
report was similar to that of Villacorta (I960). Quinlan et al. 1941 
reported estrous duration ranging between 7 and 40 hours in Afrikander 
cattle in South Africa.
Time of onset of estrus
Estrus can commence at any time of the day. Esslemont and Bryant 
(1976) reported a distribution of onset of estrus through the 24 hours 
of the day in Bos taurus dairy cows, with the greatest mounting 
activity occurring between 02.00 and 05.00 hours. Plasse et al (1970) 
found that 82.9% of estrus recorded in Brahman heifers occurred 
between 8 a.m. and 8 p.m., with peaks between 4 a.m. and 6 a.m. 10 a.m. 
and 12 noon, and 6 p.m. and 8 p.m.
27
In Zebu and African breeds in Central Africa the onset of heat 
has been found to concentrate around sunset and sunrise hours (Rakha 
et al. 1970). Various reports tend to show that the night is well 
favoured by the zebu. Rollinson (1955) in a report from Uganda, 
stated that 40% of cows came on heat at night; while cows coming on 
heat between 24.00 and 05.00 constituted 45.3 percent of the herd in 
another report from Kenya (Anderson 1944).
Estrual behaviour and ovulation
Estrual behaviour has been described by various authors (Hammond 
1927; Salisbury and Vandermark 1961; Williamson et al. 1972; JEsslemont 
and Bryant 1976). Commonly described as estrual signs are the swelling
and reddening of the vulva, clearO mrucous vaginal discharge, and raising 
and switching of the tail. Observable changes in behaviour include 
restlessness, mounting of other animals and standing to be mounted. 
Mounting by a cow at estrus is similar to that of the bull (Hafez et 
al. 1969). The at estrus is also anorexic, and might roam
over wide areas on the field doing little grazing (Hafez 1969). When 
estrual signs and behaviour are not intense and the animal does not 
stand to be mounted, the condition may be subestrus. "Silent ovulation" 
cr "silent heat" is ovulation not accompanied by estrual signs and 
behaviour# Anovulatory estrus may also occur. Anestrus is the 
stage when ovaries are quiescent and there are no estrual signs 
(Roberts 1971).
28
Some early reports stated that estrual signs and behaviour could 
not be observed in the zebu (Anderson 1936; Richard 1946). Contrary 
to these reports estrual signs have been observed in zebu and African 
breeds though the estrual behaviour was weak (Rakha et al. 1970). It 
is also believed that the zebu cow accepts the bull after long intervals 
while on heat (Rollinson 1962).
Ovulation occurs at about 24 to 30 hours after the onset of
5
estrus in the cow (Thibault and Levasseur 1975>;; Wolff J : aind Monty Jr,
1974). The range of this interval has been found to be about 16 to 
42 hours (Swanson and Hafs 1971). Salisbury and Vandermark (1961) 
summarised reports showing that cows and heifers ovulate at about 12.5 
and 11 hours respectively after the end of estrus, with a range of 2
V
hours before the end of estrus to 20 hours after estrus for cows, 
and 2.2 to 22 hours after estrus for the heifers. The interval between 
the end of estrus and ovulation which is an average of 10.5 hours as 
determined by Trimberger (1948) has, therefore been confirmed in many 
later studies, in 1974, van der Westhuysen and Venter, summarised 
reports showing that "even when estrus and ovulation occur regularly in 
cows, abnormal time relationships may cause infertility".
In addition to visual observation of estrual signs and behaviour, 
aids such as estrous-detection devices and vasectomised bulls with or 
without markers have been employed with varying degrees of success to 
detect estrus (Farris 1954; Donaldson 1968; Wagnon 1972; Williamson et 
al. 1972). The incidence of missed estrus decreases with increase in the
UNIVERSITY OF IBADAN LIBRARY
30
1960? Gangwar et al. 1965? Bond and McDowell, 1972). Afcestrus might 
be temporary and estrus might reappear some weeks after the animal 
had acclimatised to the hot environment (Gangwar et al., 1965; Bond et 
al. 1960). The latter authors found that 5 out of 6 cold-accustomed 
heifers exposed to 32°C ceased cycling after 5 weeks of treatment, but 
by 21 weeks all heifers were cycling. Bond and McDowell (1972) found 
that summer-accustomed heifers (24.4°C) did not stop cycling when exposed
to 32°C 60% RH but became anestrous at 38°C while cold-accustomed
animals ceased to cycle at 32 O C but reestablis^hed the cycles after 16 
weeks.
Heat exposure has caused a reduction in the estraus intensity of
Bos taurus heifers (Bond et al I9650; Madan and Johnson 1972). Estrus 
has therefore been difficult to detect in heat stressed cattle (Poston et 
al. 1962). The occurrence of silent ovulations, that is, ovulations not 
accompanied by estrual signs, is increased in cattle under hot conditions
(Labhsetwar et al. 1963). Silent ovulation is an important cause of
observed irregularity of estrus in cattle (Trimberger 1956). It has been 
suggested that anestrus associated with heat stress may actually be 
unobserved estrous periods, because of the difficulties associated 
with detection of estrus during hot weather.
The duration of estrus was found to be shortened in cows and 
heifers under heat stress (Branton et al. 1957? Gangwar et al. 1965;
Bond et al, 1960). Wolff and Monty Jr. (1974) reported that estrous
31
period was shortened in lactating cows but not in nonlactating cows 
in the hot season.
Hot conditions have been associated with reduced release of 
luteinising hormone (LH) corresponding with observed reduction in 
intensity of and frequency of estrus (Madam and Johnson 1973). In 
other studies on cows exposed to hot environment, progesterone 
concentration was found to be elevated in plasma (T- a and Stott
1969; Abilay, Johnson and Madan 1975) . An incc:rease :in adrenocortical
but not corpus luteal content of progesterone had also been observed 
in ' heat stressed cattle (Stott et al 1967). Exogenous ACTE 
administration has caused elevated, pilaaisma progesterone concentration
confirming, among other things, theS a>d2renocortical source of increased 
plasma progesterone in heat-stressed cattle (Gwazdauskas et al. 1972; 
Wagner et al 1972). Increased plasma concentration of progesterone
under thermal stress has been suggested as one of the causes of 
infertility in cows (Wiersma and Stott 1969). Marshal (1942) stated 
that seasonal changes in sexual rhythms are less marked in the lower 
latitudes due to the less pronounced variation in the daylight.
Contrarily, Anderson (1948) has associated high temperature and sun­
light with increased sexual function in cattle in Kenya at very lev; 
latitudes, suggesting seasonality in sexual activity of the African cattle. 
Brody (1956) also stated that Bos indicus and the crosses have higher 
fertility in spring and summer months in countries near the equator.
32
The highest conception rates and perhaps sexual activity have 
occurred in zebu and African types of cattle in South West Nigeria 
during the hot months of the year from March through June (Steinbach 
and Balogun 1971). Similarly, seasonal variation in fertility had been 
observed in zebu under extensive systems of management in other parts 
of Africa, India and Pakistan as well as in South America (Wilson 
1946? Kale 1963, Majeed 1966? Kohli and Suri 1960? uCaneiro 1950?
Jochle 1972). Because highest fertility was recorded in the hot 
period of the year, it has been suggested that heat may be triggering
off in the Bos indicus an endocrine responsse completely different from
that in the Bos taurus thus imposing a peculiar evolutionary advantage
on the former (Thompson 1973)•
Relationship of photoperiod and estrous cycles
An improved ovulation rate in spring in South African and North 
cattle
American/has been attributed to increasing day light (Van Rensburg and 
de Vos 1962; Kidder et al 1952). Spring time has been associated 
with increased sexual activity in Brahman cattle (Plasse et al 1968). 
Anderson (1948) also suggested association between increasing daylight 
and sexual activity. Thibault et al (1966) believed that photoperiod 
has a regulatory effect on estrous cycles. It has been suggested that 
the rapid increase in daylight and not the actual day length per se 
may be stimulatory to sexual activity (Farner, 1961? Steinbach and
Balogun 1971)
33
Relationship of nutrition and reproduction
High levels of nutrition has quickened the onset of puberty in 
cattle and prevented adverse winter effects on estrus and sexual 
activity (Joubert 1954; Wiltbank et. al. 1962). Feed restriction has 
been found to cause a reduction in LH in rats suggesting effects on 
the pituitary gland (Howland 1972). The deficiency of phosphorus has 
been suggested as the cause of delayed puberty in Indian zebu cattle 
on all-roughage feeding (Johari and Talapatra*/ 1957). Seasonal avail-
■ 19:
ability and quality of pasture has been associated with seasonal
fertility patterns in zebu cattle (CarneirVo, 1952; Jochle 1972). 
Increases in the plane of nutrition has been found to prevent the
occurrence of long estrous cycles and subsequent anestrus in zebu 
cattle in Central Africa during the dry season when nutritional
supply was low (Rakha and Igboo<eli 1971). When adequate nutrition was 
supplied the effect of stress on estrous cycle due to the season was 
sufficiently contained.
The widespread belief that adverse dry season or winter may 
depress fertility may therefore, to some extent^ be explained by the 
nutritional deficiency prevalent during these periods. To avoid 
confusing the effect of nutrition with that of the ambient conditions, 
the nutritional level of cattle observed from season to season should 
not be excessively altered during the period of study.
34
Fertility is reduced if the normal sequence of events during to 
estrous cycle (particularly the expression of intense estrus and 
occurrence of ovulation) is disturbed (van der Westhuysen and Venter 
1974). Sufficiently prolonged estrus increases the chance of the 
cow to be recognised at estrus, and to be bred artificially or by the 
bull. A knowledge of the time of onset of estrual behaviour is a 
useful guide for observation of estrus. An understanding of the
pattern of sexual cycles and of ovulation through the seasons is
essential for planning breeding programme2sS (Rollinsson 1962; Van Rensburg 
and de Vos 1962).
Physiology of Body Temperature
Body temperature measurement ^ y
Various locations on the body surface have been used to estimate 
the temperature of the body under different environmental,and physio­
logical conditions (Bianca 1965; Bianca 1964). The skin temperature has
been found to vary in proportion to the rectal temperature. The
tympanic membrane temperature, however, is known to be more sensitive 
than rectal temperature and to change more rapidly when environmental 
or ruminal temperature is suddenly changed (Guidry and McDowell
1966).
The temperatures of the rectum and vagina have been used to 
monitor deep body temperature in cattle (Kriss 1921; Wren et al 1958; 
Bane and Rajakoski 1960). The temperature of the rumen had similarly
35
been monitored (Dale et al 1954). Some workers measured jugular, 
pulmonary and carotid blood temperature (Bligh 1957; Ingraham and Whittow 
1961). The second group of the last quoted authors also measured the
hypothalamic temperature.
Most frequently the means of describing body temperature is the 
rectal temperature, The advantages of the rectum ove^r other locations
of the body for monitoring body temperature, include the ease of
approach to the rectum, and the facts that rectal temperature responds
to abrupt changes in environmental temperratuxrfei ronly after a short delay,
and that the changes in rectal temperature parallel the change in deep 
body temperature (Bligh 1955; Bianca 1965).
Rectal temperature may be measured by ordinary clinical thermometer, 
a resistant thermometer or a thermocouple. The demerit of a simple 
mercury rectal thermometer is said to be the possibility of hyperthermy 
being produced in the animal by excessive muscular activity due to 
struggling during the time of measurement; whereas by using radio 
telemetry, the animal can be unrestrained and not conscious of being 
under observation (Wilson et al 1971).
, Temperature regulation
In cattle, the amount of metabolic heat produced increases with 
xncrease in body weight, the level of feeding and productivity (Worstell 
and Brody 1953; Kibler 1960; Thompson 1973). Heat production in 
lactating dairy Holstein cows is, therefore, higher (30%) than in the 
heifers. (Johnson 1978). Metabolic heat production increases in
36
cattle exposed for a short period to severe heat; but it decreases 
if the animal is exposed to either a milder or a more intense heat for 
a prolonged period (Johnston et al 1958; Worstell and Brody 1953;
Kibler I960; McLean 1963) .
The heat produced by metabolism is carried to the skin surface 
by the circulatory system. At the skin surface some of the heat is lost 
by conduction, radiation and convection and the rest is used in moisture
evaporation (Thompson 1973).
Thermoreceptors found in the skin scome domestic animals have
not been demonstrated in the skin of cattle. Infrared irradiation of
the skin has been found to cause a rise in body temperature and 
respiratory rate in cattle (Findlay and Ingraham 1961). These thermo­
receptors are therefore believed to set up impulses under thermal 
stimulation which reflexly initiate hyperpxxe®. The presence of heat 
sensory receptors in the hypothalamus has been reported (Findlay and
Ingraham 1961^Hales and Whittow 1966). These are also believed to be 
present in the spinal cord (Hales and Jessen 1969)- Locally heating 
these places had caused excessive heat loss leading to hypothermia. 
Sensory nerves synapse with motor nerves in the brain which stimulate 
the different organs of the body concerned with heat loss. The
neurotransmitter here has been suggested to beJT~hydroxytryptamine 
%
(Findlay & Robertshaw 1967; Findlay and Thompson 1968).
37
Reduction in the sympathetic nervous activity causes peripheral 
vasodilation which allows more heat to flow to the skin. Vasodilation 
would occur .in thermoneutral environment hence it is not an important 
way of losing heat (Thompson 1973). Some of the body heat is conducted 
to the surface of the coat. At the coat-air interphase the heat is lost 
to the environment by physical means, that is, radiation, convection or 
conduction.
Heat loss by conduction to the environment is not important in 
cattle in a hot environment. Dairy Holstein cows have,, however, been
observed to.^ie in mud and/or
showing heat sensitive cattle might desire to lose heat by conduction 
(Seath & Miller 1947; Romanance-Pounce et al 1977).
Heat loss by convection from the coat surface to the surrounding 
air is influenced by wind velocity, direction of air movement and shape 
of the animal*s body (Kibler and Brody 1954a; Thompson 1973). The
texture of the coat is also important: the short stiff zebu hair allows 
better air movement than the long curly hair of Bos taurus (Dowling
1959) through the skin surface by radiation depends on
coat colours: the light or cream coloured coats are known to reflect 
infrared radiations more than darker coat (Rhoad 1940a; Bonsma and 
Louw 1963; Reimerschmidt 1943).
Cutaneous evaporation is due to moisture normally diffused through 
the skin and also produced by sweat glands* The population density and 
volume of bovine sweat glands vary slightly between different breeds
(Nay and Hayman 1963). They have been found to be higher in Bos
indicus than in Bos taurus (Nay 1959; Taneja 1960).
Climatic factors influence sweating activity in cattle. 
Increasing environmental temperatures have been found to stimulate 
sweating in cattle from about 18°C (Kibler and Brody 1950). The 
depressing effect of high humidity on sweating has been noticed only 
at very high environmental temperatures (35°C) (McDowell et al. 1961). 
At high environmental temperatures, ventilation has increased evapora­
tive heat loss (Ragsdale et al. 1950). Solar radiation increases
sweating by increasing the skin temperatOurve. It has, therefore/ been
shown to be responsible for the higher rate of sweating under field 
conditions than in hot climatic laboratories (Murray 1966). Cutaneous 
evaporation was found to rise when cows were exposed to radiation at 
low environmental temperatures (Kibler and Brody 1954).
Cutaneous evaporation has been found to be higher in Bos indicus 
calves than in Bos taurus under conditions of heat stress (Kibler and
Yeck 1958; Kibler and Yeck 1959). Friesian cattle have been found to 
develop a greater number of sweat glands than African types of cattle 
when raised under Nigerian and Egyptian conditions (Amakiri 1974;
Shafie and El-Tannikhy 1970). The ability of Bos taurus for greater 
cutaneous evaporation improved when the animals were raised at high 
temperature environment (Kibler and Yeck 1959). It is not known if 
the increased sweat gland population in the Friesian cattle acclimatised
39
to tropical Nigerian condition is associated with high sweat production 
which should reflect in lower respiratory rates.
Some quantity of body heat is utilised in evaporating moisture 
at the respiratory surfaces. Respiratory moisture loss, therefore, is 
directly related to respiratory heat loss. From the works of Ingraham 
and Whittow (1962) and Rligh (1957), it has been suggested that the 
main cooling effect of respiratory evaporation takes place in the upper 
respiratory passages and not in the lungs. t e .  is. however a limit to 
the importance of the respiratory activity in losing body heat since 
respiratory evaporation is low compared to cutaneous evaporation, the
ratio of the contributions of the latter and former to total surface
moisture loss being 6:1 (Bianca 1965).
Under conditions of heat- stress in the psychrometric chamber, 
cattle exhibit polypnea to a degree which depends on the magnitude and 
duration of the heat stress. Heat sensitive types of cattle are 
particularly morre affected (Worstell and Brody 1953; Kibler et al 1965;
Bond and McDowell 1972; Johnson et al. 1967). In this respect, cattle 
are unlike man, but are similar to a few mammals including swine, sheep, 
mice, rats, dogs and cats (Findlay 1954). Increases in respiratory rate 
occur if demands for cooling continues (Bianca 1958). Respiratory 
activity in cattle under conditions of heat stress has been suggested to 
be a measure of the inadequacy of the more important cutaneous evapora­
tion to maintain a temperature balance (Riek & Lee 1948).
40
It has been shown that polypnea * does not prevent a rise in body 
temperature in calves and heat sensitive cows (Bianca 1962? McDowell et 
al 1953). This is probably because the respiratory muscles generate 
more heat during fast breathing or panting in a hot environment. It 
has, therefore, been shown that oxygen consumption is increased in 
cattle under heat stress (Hales and Findlay 1968). Under similar 
conditions, blood lactic acid is increased, and respiratory alkalosis 
can develop (Bianca and Findlay 1962). The respiratory response of 
cattle to progressively severe thermal stress occurs in two stages, 
the first which is panting, is followed by slow deep breathing which
has no significant metabolic cost (Ha&les and Findlay 1968).
Reports from field studies also show that respiratory responses of 
cattle vary with the weather conditions, increases in respiratory rate
occurring in hot weather (Byerman and Morag 1971; Rainey et al 1967?
Wolff and Monty Jr 1974?* McDowell et al. 1955; Berman 1967).
The capacity of cattle to dissipate heat through evaporation is low 
thus making them particularly susceptible to thermal stress. When the
body of he‘aA  tf -  sQ iensitive cattle gains heat, the deep body temperatures of 
cattle do not rise at environmental temperatures below 70 - 80°F 
(21 - 26°C) Kibler and Brody, 1950). Many studies in the climatic 
laboratory have demonstrated the response of body temperature in cattle 
to increasing environmental heat (Worstell and Brody 1953; Kibler et al 
1965? Johnston et al 1963). Studies in the field have also demonstrated
41
similar phenomenon in cattle. This is more pronounced in animals under 
stress of lactation than in non-lactating cows (Wolff and Monty Jr., 1974) 
Non-lactating cows have been found to show little or no seasonal 
differences in their rectal temperatures (Wolff & Monty Jr., 1974).
Normal body temperatures may be affected by the nutritional level 
(Robinson & Lee 1947; Rogerson 1960). The temperature of the jugular 
vein blood has been found to increase as a result^ of feeding cattle. 
(Ingraham and Whittow 1961).
Periodic fluctuations may occur in the0 d*eep body temperature 
without compensatory reactions being brought to play. For example, 
diurnal patterns in body temperature with an early morning minimum and 
early evening peak has been observed in cattle (Gaalaas 1945; Kriss
1921). When body temperatures of cattle were recorded continuously 
67% were diphasic having 2 peaks a day^ 23% were polyphasic and 3% were 
aphasic. Ovariectomy and pregnancy did not affect the incidence of 
these patterns (Wrenn et al 1961). This circadian shift in thermo­
regulatory functions has been demonstrated in both the Bos taurus and 
Bos indicus types of cattle under natural environment (Rainey et al. 
1967; Berman and Morag 1971; Moran 1970; Bligh and Lampkin 1965).
When Holstein cows were exposed continuously to the sun, the 
highest body temperatures occurred in the afternoons and the lowest in 
the mornings (Rainey et al 1967). However, no significant difference 
occurred in the circadian variation in deep body temperature of Bos 
indicus and Bos taurus breeds grazing under moderate atmospheric
42
temperatures (Bligh & Lampkin 1965) . It has been suggested that the 
ability of cattle to thrive in the tropical region could be better 
indicated by the diurnal variation in the body temperature rather than a pai 
ticular body temperature (Kendal 1946). Brown et al. 1969 also suggested
that the rate of rise in the body temperature can be used to identify 
heat-sensitive cattle.
Hutchinson and Mabon (1954) found more decreases in morning
rectal temperatures in zebu cattle in the hot season than in the cold 
season in Tanganyika. Initial rectal temperatures were also lower in
heat-acclimatised calves than in non-acclimatised calves on exposure 
to hot humid environment (Bianca 1959 a, b). Non-lactating Holstein- 
Friesian cows were found to show lower morning rectal temperatures during 
the hot summer months than in the cooler season in Arizona (Wolff and 
Monty, Jr. 1974). Bianca (1959b) believed that the lower body
temperature before heat exposure are beneficial because they signify a
low starting point for the animal in its defence against hyperthermia. 
Seasonal depression in the morning rectal temperature coinciding with 
the hottest months of the year is suggested to be of a similar 
thermoregulatory advantage by preparing the animal for the heat of the 
day and delaying, but not necessarily preventing, hyperthermia (Wolff
& Monty Jr. 1974)
43
Cyclic changes in the body temperature of cattle in relation to 
estrous cycle have been studied (Wren et al 1958; Bane and Rajakoski 
1960)• Marked depression in the body temperature occurred two to three 
days before estrus. The body temperature was elevated on the day of 
estrus, depressed on the day after, coinciding with ovulation, and 
remained depressed till the 7th day of the cycle when an elevation
occurred until the approach of the next estrus a field study, no
consistent relationship was found between the rectal temperature and the 
ovulation time (Howes, et al. 1960).
As regards breed effect, Worstell and Brody (1953) reported that 
no significant differences could be observed among breeds of Bos 
taurus. The study by Bligh and Lampkin (1965), quoted above,also showed 
that species differences between Bos indicus and Bos taurus in rectal 
temperature was insignificant under moderate climatic environment.
Heat tolerance C O'
Heat tolerance is a measure of the extent to which the animal can 
maintain normal body temperature and other physiological functions on 
exposure to a hot environment. Various methods including body 
temperature changes, respiratory evaporation, skin evaporation, produc­
tivity, skin and hair coat characteristics have been used to determine 
heat tolerance in both field and laboratory studies? and the relative 
usefulness of these had been well assessed (Bianca 1961? McDowell 1966). 
Body temperature activity has been more generally preferred and various
44
field tests make use of this parameter in assessing adaptability of 
cattle to a hot environment. Comparisons have been made between Bos 
indicus and Bos taurus types of cattle both in the field and in the 
climatic laboratory regarding the effect of air temperature on body 
temperature. It has been shown, for example, that under hot conditions 
the Brahman (zebu) maintained its body temperature best, the Aberdeen 
Angus (Bos taurus) least well, and crossbreds gave results which lay 
between those for the other two (Rhoad 1938; Rhoad 1940a).
On the basis of experiments similar to this, Rhoad (1944)devised 
the Iberia Heat Tolerance Test by which a heat tolerance coefficient 
o f cattle is calculated from the in crease of rectal temperature whichoccurs during a day in an unshad<ehd environment of 90o F in, the sun.
The formula employed is: A° = 100 - 10 (BT° - 101), where A° is the
heat tolerance coefficient and BT°,/the body temperature. Perfect
efficiency in maintaining body temp“er ature at 101 oF, the average rectal 
temperature of cattle, holds when the adaptability coefficient is 100. 
On this basis, adaptability of a number of cattle types had been worked 
out and Bos indicus and half-breds have been shown to possess higher 
heat tolerance than pure Bos taurus (Rhoad 1944). The same method 
had been used to test different breeds in the field in Greece (Phillip 
1949). The adaptability coefficient for the White Fulani cattle has 
been shown to be 90 (Hill 1960). The differences in the respiratory 
rate under r hot conditions have also been used to determine dif­
ferences in heat tolerance in animals with similar rectal temperatures.
45
•Some laboratory methods also make use of the rectal temperature for 
assessing heat tolerance in cattle (Lee and Phillips 1948; Bianca 1962; 
Bianca 1963). Bianca (1962) stressed that the rate of rectal temperature 
rise could be used as an indicator of heat tolerance. It has been 
emphasised, that rectal temperature if properly used is the single 
most reliable indication of deep body temperatur5ef and the best physiologicacriterion for heat tolerance (Bianca 1961; Bianca 1965). Factors thatinfluence heat tolerance include age, levels lutrition and production
breed and species genetic differences, coat colour and hair type.
Between the ages of 2 to 24 months, the heat tolerance of cattle
has been found to be low in Bos taurus (Riek and Lee 1948; Schein et
al 1957). A similar report has been given for African types of cattle
(Walker 1957). Heat tolerance increases as the animal matures (Bonsma
1949; Gaalas 1947). ALactating cows show greater rise in respiratoryrate and rectal temperature than non-lactating cows (Worstell and Brody 
1953; Scheim et al 1957; Wolff and Monty Jr. 1974; Johnson et al 1962; 
Kibler et al 1965). Increasing milk production is associated with a 
decline in heat tolerance (Brown et al 1969). Sudden increases in the 
level of feeding have been found to depress the heat tolerance of 
heifers (Yeates 1956).
Various studies have obtained results similar to the report by 
Rhoad (1944) showing the species differences in heat tolerance 
(McDowell et al 1953; Bonsma 1949; Schein et al 1957; Johnston et al
1963). Johnston et al (1963) found that rectal temperatures of Red
46
Sindhi (Bos indicus) bulls were significantly lower than those of the
Holstein and Brown Swiss at both temperatures of 82 and 104 oF. The 
level of tolerance has been shown to increase with the amount of the Bos 
indicus blood in the crosses between Bos indicus and Bos taurus types 
of cattle (Rhoad 1944; McDowell et al 1953)* The superiority of the 
Brahman to Holstein and Jersey in heat tolerance has been attributed to 
the surface structures such as the dewlap, navel fold, brisket and the 
hump which tend to increase surface area/body weight ratio, and to a 
superior radiating coat, slower rate of hair growth and greater ability 
to sweat (Phillip 1949). In a field study, slight breed differences in 
heat tolerance were observed between Holstein and Jersey, being slightly 
higher in the latter (Seath and Miller 1947). Similarly, Romance- 
Pounce et al (1977) found that rectal temperatures differed between 
Holstein, Guernsey, Jersey and Brown cows exposed to natural hot 
climate, with values decreasing in the order of the breeds.
The hair and colours influence the heat tolerance of the
animal by determining the amount of solar radiation absorbed or 
reflected. Red, yellow or redish-brown hair reflects heat or infra-red 
rays; yellow, redish-brown or black hair reflects ultra-violet (short­
wave) rays. Cream or light-coloured coats reflect more visible radiation 
than dark-coloured coats (Riemerschmid 1943; Bonsma 1943). It is 
believed that white, yellow or red coat with dark hide is the best 
combination to render the animal resistant to high temperature and
47
intense radiation of the long-wave (heat) and short-wave rays which 
are most prevalent in the tropical and sub-tropical regions. This 
combination of hair and hide colours is possessed by tropical breeds 
of cattle (Riemerschmid and Elder 1945; Bonsma 1949). Bos indicus 
cattle generally have shorter and lighter coats than Bos taurus (Hayman 
and Nay 1961) .
Other hair characteristics aid heat resistance. The thick, 
stiff and short medullated hair fibres of the zebu type enhance air 
movement at the skin surface, thus aiding vaporisation of moisture, 
and are highly correlated with heat tolerance (Dowling 1959). The 
white coat of the Fulani cattle is 100% medullated, short thick stiff 
and glossy (Hill 1960). That of most temperate-evolved cattle is 
naturally long, curly and wooly in texture. The hair of the Holstein 
cattle reared in Nigeria has been modified into relatively shorter 
form by the long exposure to tropical environment, though it has not
attained the shor&tnes cs of the coat of the zebu types (Amakiri 1974).
Wooly animals have been found to show greater increases in body 
temperature than glossy coated animals (Bonsma 1943). Berman and Volcani 
(1961) showed that the thickness of hair coat varies with the season, 
minimum values occurring in spring and summer. Such seasonal variations 
may also cause seasonal changes in the effect of hair coat on heat
tolerance
48
Influence of shade on thermoregulation
Rainey et al (1967) found that the body temperature and 
respiratory rates of cows in the shade were lower than in animals in 
the sun. In another more recent field study involving Holstein, 
Guernsey, Jersey and Brown Swiss cattle, it has also been shown that 
shade provides a micro-environment for the animals and modifies their 
physiological responses (Romance-Pounce et al 1977). Heat intolerant
animals have been reported to seek shade w<h?hile in the field (Seath and
Miller 1947; Romance-Pounce et al 1977). >
Kelley et al (1950), proposed that shade structures with high 
roofs, referred to as high shade, would provide more comfort than 
structures with low roof (low shade). The higher efficiency of high 
shade has been attributed tb the fact that the animal can lose more 
heat by radiation to the clear sky (Kelly et al 1957).
Besides the fact that the physiological responses are ameliorated, 
the reproductive efficiency has been found to be improved in shaded
animals compared to animals exposed to the sun (Wiersma and Stott 1969;
Romance-Pounce et al 1977) . Milk yield is also improved when cows are 
reared in the shade (Romance-Pounce et al 1977).
Climatic heat stress factors
The principal climatic heat stress factors include the environmental 
temperature, radiation, humidity and wind. The wind is a stressful 
factor only when the environmental temperature exceeds body temperature.
Under such conditions, the inhaled air is cooled as it passes through
*
the respiratory tract and the animal gains heat, (Hales and Findlay 
1968).
The combined effect of high temperature and humidity have been 
regarded by various workers as heat stress causing increases in the 
physiological responses (Worstell and Brody 1953; Beakley and Findlay 
1955; Cargill et al 1962; Johnson et al 1963; Kibler 1964). The 
relationship of temperature-humidity index to production and certain
aspects of reproduction have been examined in cattle (Johnson et al 
1963; Thatcher 1974). "High environmental temperature without its 
relation to humidity of the air does not express the. severity of the 
environmental condition” (Johnson et al 1963).
Bianca (1963) found no difference in the order of heat tolerance 
of calves in each of 10 environments having different combinations of 
relative humidity and temperature. Crossbreds (h Jersey x k Brahman) 
were also reported to be more affected by changes in air humidity than 
pure Holsteins and Jersey cattle; and this was attributed to the higher 
sweat production in the crossbreds (Quazi and Shrode 1954). High humidity 
causes a reduction in the vapour pressure gradient between the skin and 
air, and therefore inhibits evaporative moisture loss.
High humidity may not always considerably^ affect cutaneous 
moisture loss by the animal. Mclean and Calvert (1972) found that at 
an environmental temperature of 35°C a reduction of vapour pressure 
by increasing the relative humidity of the air from 32 to . 72% had only a
50
slight effect on skin evaporative moisture loss. This was explained 
by assuming that the rate of sweat secretion was unchanged and an 
increase in air humidity caused a temporary reduction in evaporation 
and a build up of moisture on the skin. As a result*the vapour 
pressure of the skin surface increased automatically re-establishing 
the vapour pressure gradient between the skin surface and air until 
evaporation rate was in equilibrium with the rate of sweat secretion. 
When extremely high levels of humidity wai s applied, these workers 
obtained marked reduction in evaporation. In the context of the
Southern Nigerian situation, relatively high humidities occurring
during the wet season may not nece ssarily be high enough to disturb 
cutaneous evaporation in cattle in the field. McDowell et al (1961) 
reported that humidity-induced decrease in cutaneous evaporation in 
Holstein can only occur at a temperature as high as 35°C. Ojo (1973) 
suggested that about July in the wet season, high temperatures combined 
with high humidities in areas including the middle belt of Nigeria 
could impose heat load on cattle? Ibadan area was excluded because 
of the relatively lower air temperatures occurring there at that time 
of the year.
High humidity enhances the effect of high air temperature on 
respiratory activities. Air temperatures of 30° and 35°C at high humidity 
have been found to be equivalent in their effect on respiratory 
rates in calves to air temperatures of 33°C and 40° respectively at a 
low humidity (Beakley and Findlay 1955). Expired air is almost
51
saturated with moisture at body temperature (McLean 1963). It would 
be expected that if the humidity of inspired air is high, it would 
directly reduce respiratory evaporation and respiratory evaporative 
heat loss for a given respiratory minute volume, McLean and 
Calvert (1972) however found that increasing the relative humidity
of atmospheric air from 32 to 72% at an environmental temperature of
35 oC, while causing an increase in respiratory frequency, only slightly 
reduced respiratory evaporation. The increased respiratory frequency 
was suggested to be reflecting an effort towards a compensatory 
increase in respiratory minute volume which would tend to resolve 
respiratory evaporation to the no4r<mayl level. Under field conditions,therefore, moderately high humidity may not necessarily cause a reduction 
in respiratory evaporation or be stressful in cattle.
Solar radiation is effective as a strong heat stress factor 
in the field, causing rectal temperature and respiratory rate to rise 
in cattle (William et al 1960). Solar radiation was found to influence
body temperature even at environmental temperatures below 32°C. Buffaloes 
are particularly very sensitive to solar radiation exhibiting greater 
responses than Harina (Indian zebu) cattle in the sun in India 
(Badreldin & Ghany 1952, Mullick 1960). The potential influence of 
solar radiation in imposing heat load on cattle at different locations 
and during different periods of the year in Nigeria had been studied 
(Ojo 1971). The author showed that solar heat load increases inland 
from the coast and is lower during the wet season. This is suggested 
to be probably due to higher cloudiness in the south and in the wet
52
season which reduces the amount of incoming solar radiation.
Among the climatological variables, air temperature has been 
found to be the most important with respect to environmental heat 
stress in cattle under conditions prevailing in Texas. The same 
changes in respiratory ifate, rectal temperature and heart rate were 
obtained when air temperature alone or a combination of all the 
climatological variables was applied (Shrode et al 1960).
Environmental temperature is said to be the "most imjiportant climatic
factor** that may modify the ability of cattle3 toO secrete milk (Johnson
1965). it has been said that "dry and ulb temperatures, solar
radiation or hours of sunshine, air movement, and precipitation patterns 
for an area near the animal will suffice for assessment of climatic 
stress** under field conditions (McDowell and Johnson 1971) .
Climatic stress, therefore, results from effects of these factors 
all of which act either singly or in combination to influence the
physiological system of the animal (Rhoad 1940; Lee and Phillip 1948; 
Kibler and Brody 1954a). However, generally under hot conditions, 
wind or ventillation, especially with relatively high velocities of 
5-9 mph, widens the comfort zone of the animal by increasing the 
convective and evaporative heat exchange between the animal and the 
environment (Kibler and Brody 1954b). It has been found that such 
effects of the wind is not felt by the Brahman cattle until air tempera­
ture 6f 95°F is reached or exceeded (Kibler and Brody 1954b; Findlay
1954).
53
MATERIALS AND METHOD
Experimental animals
The two breeds of Bos taurus, Holstein-Friesian and German 
Brown were imported to the University of Ibadan Teaching and 
Research farm between 1969 and 1973 from Western Germany. A White
Fulani ( Bos indieus) dairy herd on this
established over twenty years ago under a ect
trypanosomiasis resistant animals of this breed. White Fulani 
cattle are naturally accustomed to the hot tropical climate of the
Six, five and six heifers of the Holstein, Brown and Fulani 
respectively with ages ranging from 16 to 2k months were used for 
the present investigation. They had a mean initial weight of
The heifers of the Holsteins and Browns
were selected from the first generation heifers of imported cows. 
In selecting the experimental animals, the maturing heifers were 
observed for expression of estrus; and ovaries were examined by 
palpation per rectum for changes (presence of corpus luteum, or 
follicles). The ages of the animals when ovaries showed changes 
were noted. The heifers were all cycling normally before the 
commencement of the investigation.
54
The Brown and the Holstein cattle evolved in the temperate 
regions of the world and are not adapted to tropical climate. In 
the strict sense, neither the experimental Bos taurus nor Bos indicus 
(zebu) cattle belong to the forested subequatorial zone of 
Southern Nigeria.
Climate of Ibadan
Ibadan lies at latitude 7° 2 North and 3U 5*+' East at 
an elevation of about 227 meters above sea level (Church 197*0; 
it has a lowland rainforest vegetation (Keay 1959)* It is about
1UU kilometers inland from the Western Coast of Nigeria.
The climate of Ibadan w  een described as seasonal- 
equatorial which is characterised by slight seasonal changes in
temperature and daylight period. There are two main seasons: 
the dry and the wet seasons (Church 197*+) -
At the University of Ibadan, the mean monthly minimum and 
maximum temperatures for the last 20 yearswere 70°F (21.1°C) and 
80°F (26.6°C), and for the year 1976, the values were 69°F (20.5°C) 
and 80°F (26.6°C) respectively. The two rainfall maxima occur 
in June - July and September coinciding with the equinoxes.
The total precipitation for the year 1976 was 877.2 milliliters.
The dry season, extending from November through early March, 
is characterised by high afternoon temperatures (maxima temperatures 
varying between 82 and 98°F) with high diurnal variations
55
(about 23 - 26°F) 3 low afternoon humidities (15 ~ 77 RH and 
low precipitations (0 - 125mm/nonth). The wet season extends 
from mid or late March to September and is characterized by high 
temperatures which are relatively lowered in the wettest months 
(maxima temperatures varying between 76 - 95°F), high afternoon 
humidities (52 - 9  ̂RH %),high precipitation (63 - 2 18 mm/month)
and light to heavy cloud cover. Diurnal variation of temperatures 
is low (about 10 - 13°F). The highest humidities and lowest 
dry bulb temperatures occur at 0 7.0 0 hour; and the lowest 
humidities and highest dry bulb temperature occur at 16 .0 0 hours 
in the two seasons. Total sunshine hours decrease from December in
the dry season to August in the wet season (237 to 6 9 .8 hours/month 
in 1975). S
Overlapping of the two main seasons may occur sometimes, so 
that the months of March and October may be quite wet in some 
years and;vin other years, may be dry with little precipitation.
The year may be divided into four quarters.
(1) December through February is dry and hot. The
dry hazy and cold 'harmattan' winds blow in December 
and January making the daily minimum temperatures 
relatively low and resulting in cold nights and mornings.
56
(2) March through May represents the transition to the 
wet season and is hot and wet with lower diurnal 
temperature range than in quarter (1). Rainfall 
may range from medium to heavy.
(3) June to September represents the wettest period,
hot especially in June, and humid, but relatively cool 
in July and August. The cloud cover is highest at that 
time with low diurnal temperatures and high humidities.
(k) Late October through November represents the end of the 
rainy season and the beginning of the dry season. 
Precipitation gradually diminishes through October to 
very low or nothing in November; temperatures are high 
with marked diurnal ranges, and cloud cover and relative 
humidities are low.
The changing seasons are dependent upon the movement northwards 
during the wet season and southwards during the dry season of the 
Intertropical Convergence Zone (ITCZ) which is determined by the 
interplay of two major winds in West Africa. The dry north easterly 
winds are predominant in the dry season causing dry hazy weather with 
cold nights and mornings. The south westerly winds are predominant 
during the wet season and are associated with much cloud cover and 
rain. For the purpose of the present investigations, meteorological 
records from November 1975 through February 1977 were obtained from the
57
Department of Geography, University of Ibadan. All recordings were 
made at the meteorological station located within the campus and 
at a point less than 1 kilometer from the University farm.
The weather conditions from November 1975 through December 1976 
are tabulated (table A9) and represented graphically (Fig. 5). The 
relationship of air temperature to the relative humidity during the 
period when blood samples were collected are £ shown xn a 
histogram (Fig. 6).
Air temperatures were high from late October through April 
ranging from 86.5 - 97.1°F (30-36.2°C). The highest air temperatures 
occurred in March with average maximum temperature of 92.1*°F (33.6°C). 
July to August period was cooler with lower air temperatures; 
average maximum temperature was 81°F (27.3°C). Average minimum 
temperatures were 6U.5°F (18.1°C), 71.6°F (22.0°C), 68.1°F (20.0°C), 
and 69.0°F (20.6 r December - January, March - April, July - 
August and late October through November periods respectively.
More rapid rise in air temperatures occurred in the mornings during 
March - April period than in other periods of the year. Relative 
humidities at 16 .0 0 hours when maximum temperatures were recorded, 
were h2. 6, 5̂ .*+, 76.0 and 55.9 percent for December - January,
March - April, July - August and late October through November 
periods respectively and were, therefore, highest during July - August
58
period. Air was thus driest during Decenber - January period but 
nonetheless cold in the evenings through the night and morning due 
to the prevalent cold winds blowing till the middle of January.
Rainfall occurred from March through the middle of October; 
there was a short "August break" in the later half of August till 
early September when precipitation was very low'W. . VOJtUJher months had 
little or no rain.
Sunshine hours were during the drier months and lowest
in July - August period. A very important feature was the intense 
sunshine in the afternoon, especially when the sky was cloudless.
Experimental design
Blood samples were collected during periods selected from the 
four quarters of the year described above. Breathing rates 
(respiratory rates) and rectal temperatures were recorded. Behavioural 
responses to heat particularly shade seeking9 were also observed.
The periods selected were early December 1975 through the middle 
of January 19T6 s early March through the middle of April 1976* 
early July through the middle of August 19765 and late October 
through November 1976. Each period lasted k2 days.
The character of estrous cycles was observed throughout the 
year. Ovarian changes were observed by palpation per rectum.
59
The heifers on experiment were kept in two adjacent pens. The 
length, breadth and height of each pen were 9 6, 63*5 and 90cm 
respectively. The pens were open on the sides and were only 
separated by metal crossbars and had a high corrugated roof and 
concrete floors which were covered every morning with wood shavings
after the pens had been cleaned.
One Fulani bull was selected, vasectomised< a2nd made to join
the heifers. An already vasectomised Brown x Ndama (BN) hull also 
joined the heifers. These two bulls were used as teasers for
detecting estrus in the heifers.
Heifers stayed in the pen fr<om  about noon till the next morni. ng
(06 - 0 7.0 0 hours) when they were released to graze on the improved 
pastures mostly of giant star grass ( c y n o d o n  Sp.) in the paddocks
adjoining the pen. s  i.n the pen, they were fed with grass and
.concentrate: the latter was composed of guinea corn or maize 
65$, palm kernel 1 5$* groundnut cake 20$, and served at the rate of 
1kg / 123kg body weight/day. Grass (mainly giant star species) 
was served at the rate of 1 kg/13.0kg body weight/day.
During the dry season when grass was minimal in the paddocks, 
the amount of grass supplied in the pen had to be increased to kg/ 
JJ kg body weight/day. As grass supply dwindled, a day' s supply 
had to be supplemented with brewers1 grain. Alternatively, corn
60
silage was served at the rate of •} kg/7 kg bo$y weight/day.
Water was supplied ad libitum in concrete troughs that run the 
breadths of the pens; salt licks were also available.
The routine health programme for the animals included faecal 
examination, deworming, spraying with insecticide, samorin prophylaxis 
against trypanosomiasis and inoculations against anthrax, heart water 
disease, foot and mouth disease, rinderpest and haemorrhagic septi­
caemia. Wet preparations'of peripheral blood from all heifers were
examined regularly for trypanosomes; but no posi.  ti.  ve case was obser„ ved
throughout the period of this study ugh tsetse flies were caught
regularly on the farm. Packed cell volume determined in the 
conventional way and haemoglobin concentration by Gyanmethaemoglobin 
method were within normal ranges (Saror and Coles 1973 j Olusanya
1976) (tables A10 and iO.
The heifers were also weighed every month (Fig. 6). The 
growth rate in the heifers through the year was not of the steady 
and uniform fashion observed in the heifers raised in the temperate 
region (Brody et al. 19̂ 7; Bachner i960). Marked weight increases 
coincided with the two rainfall peaks in April to June and 
September. A slight drop either in absolute body weight or weight 
gain occurred in the dry season. The lack of uniform growth rate 
throughout the year may be attributed to the effects of climate and
61
some nutritional inadequacies.
Generally, the coat of the Bos taurus heifers was less hairy 
during the dry season. The coat colour of the Brown heifers 
became lighter in that season than in the wet season when it was 
of a deeper brown lustre.
Other pens in the house
either pregnant or yet to be
mature age and breeding weight. Animal attendants worked on shift 
basis. Morning shift started at 6.00 hours and ended at 1U.00. 
Afternoon workers started at 13.00 hours and closed at 18.00 hours. 
Their services and those of the night-watchmen were employed 
for most procedures carried out on the animals. Apart from these
workers, an assistant was permanently assigned to take care of the
experimental animal&s. He assisted in the general management and 
handling of the animals and in recording observations. His 
duty hours had to be adjusted from time to time to suit the needs 
to carry out observations and some procedures demanded by the study. 
Since the animals were to be exposed to the routine on the
farm during the time of the study, it was decided not to 
catheterise the heifers but to train them adequately enough to get 
used to handling and blood collection by venipuncture.
62
Every morning by 0 7 .0 0 hou»j th© ojainalo ws?9 pa«scd "through 
the fenced passage leading to the crush located in a paddock close 
to the animal house. They were stopped one by one in the crush; 
some blood, about 2 - 5  ml5 was collected by jugular venipuncture. 
Ovaries were frequently examined per rectum. After all the animals 
had passed through the crush, they were led into one of the 
paddocks close by to graze till about 1 1 .0 0  hours when they were 
returned into the pens.
During this training peri. od, the ani. malso es tabli.shed a 
hierarchy of dominance, and there was no real fighting since animals
lower in the hierarchy tried to avoid animals higher in the order.
They also formed a leadershi. p - foll^ow ership order of enteri. ng
the passage and the crush, as some heifers entered the crush 
first and easily before others could be made to follow. The very 
docile BN bull, however, facilitated the entry of the heifers into 
the passage since he entered the passage and the crush easily.
There was a tendency for a more dominant animal to stay behind 
the animal lower in the established order, which gave rise to 
rear butting and pushing. The animals had to be reorganised 
and were made to follow the BN bull in the descending order of the 
established hierarchy. The arrangement was permanently followed 
and there was no disturbance among the animals. Because the Fulanis
63
tended to stay together most of the time, they were made to enter 
the crush last, the most docile among them first and led by the 
Fulani bull. The training period lasted five weeks.
The routine of jjassing the heifers through the crush before 
grazing in the paddock was continued everyday throughout the year. 
During the periods when blood samples were not collected, the 
recording of the rectal temperatures of the heifers was continued 
while they passed through the passage and crush and ovarian
examination per rectum was done when there was a need for it. 
During the marked four quarter&^&f the year, the rectal
temparatures were recorded with a veterinary thermometer inserted 
into the rectum, and the breathing rate by counting flank 
movements. Normally the heifers were used to the procedure of
rectal temperature recording every morning and afternoon. If 
approached carefully and slowly, the temperature could be recorded 
in the pen without any excitement.
For the purposes of this investigation, the breathing rates were 
recorded in the pen between 0 6 .3 0 and 0 7 .2 0 hours in the morning. 
Immediately after that, the animals were moved out gradually and 
lined in the weighing race approaching the crush. The rectal 
temperatures were recorded by an assistant while the animals were 
being bled one after the other. The afternoon readings of the rectal
64
temperatures and respiratory rates were recor*ded in the pen
between 1U.00 and 16.00 hour:;. The results were tested by analysis 
of variance, the sources of variation being breed, season, and time 
of the day (Snedecor and Cochran 196T)-
Ten milliliters of blood were collected by jugular 
venipuncture between 0 7 -1 0 and 3.00 hours into heparinised tubes 
which were then cooled in iced water. The tubes were centrifuged
at 3000 rpm for 10 minutes and plasma was separated and stored
frozen at -20 o C unti. l the ti. me for the assayVy.»
Restraint and blood collectjion were carried out very rapidly 
and noise was strictly avoided. When the collection time was 
unduly prolonged or an unusual excitement was displayed either 
before getting into the crush or at the time of bleeding> the 
animal was not bled, so as to avoid excessive variation in plasma 
cortisol levelsS.
Plasma co:rtisol concentration was determined by radioimmunoassay, 
The mean valulees of four heifers of each breed that showed the best 
growth rate and were most amenable to the procedure of blood 
collection were used in constructing the composite graphs of the 
values through the estrous cycles.
Values of plasma cortisol obtained in the heifers during each
quarter representing uneven numbers of observations were subjected 
to analysis of variance. Values obtained 'on alternate days,
65
representing fairly even numbers of observations were similarly 
treated because of the missing values on some days and because 
during October - November period, plasma cortisol was determined 
on alternate days except around estrus. Plasma cortisol levels 
on the day of estrus, the middle of estrus cycle and mean for 
the cycle were also subjected to analysis of variance, the sources 
of variation being breed, season and stage of the cycle.
In order to observe the behavioural responses to heat while ih 
the field, the heifers were grazed at least 10 times during each
quarter in paddocks which had treesprovide shade. The 
animals under shade at 12.00 hou:rs were noted. The total number
of days when an animal was fo3und? to seek shade was scored against 
her as a percentage of the total number of days of observation, 
and the result was treated by analysis of variance, sources of 
variation being breed and season. The grazing behaviour of the 
heifers was also observed.
The diurnal and circadian variations in the physiological 
responses were investigated in the heifers. Respiration and rectal 
temperatures were recorded in the heifers while in the paddock and 
unshaded on three hot days in March 1977. The heifers were kept 
grazing in the paddocks adjoining the weighing crush throughout 
the day. They were carefully mustered and passed into the passage 
approaching the crush each time the rectal temperatures were to be
taken, although many of them would stay and allow the temperatures 
to be taken while grazing. Breaths per minute were counted before 
the animals were passed through the crush and before grazing. 
Readings were taken at 07-8.00, 10.30-11.00, 15.30-16.00 and
18.00 hours. On another two consecutive days, the animals were 
kept in the pen and both breaths per minute and rectal 
temperatures were recorded at 7 .0 0, 1 0 .00-1 1 .0 0, 1H.0 0, 1 7 .0 0,
2 0 .0 0 and 23.00 hours. In addition, readings were taken
at the times given above and at 0 1.0 0 and 0^:3 .0 0 hours in the 
pen on one occasion. The readings were all subjected to analysis 
of variance. Correlations between the responses were tested as 
well as between the responses and the ambient temperatures.
In investigating the diurnal and circadian variations in 
plasma cortisol in the heifers, blood samples were collected at 
various times and under different conditions during the year.
The investigations were $r ourai as £our eXperiments.
1: In the first experiment, blood samples were collected 
in the morning, afternoon and evening in heifers kept outdoors 
throughout the sunny day. For a week in April 1976, before the 
end of the second quarter (marked for morning blood sample 
collection), the heifers were taken through the routine of passing 
through the crush when returning from the field into the pen 
between 11 and 12.00 hours. For four days after the end of the
67
quarter, the frequency of passing the heifers through the crush
in the afternoon was increased. The heifers were kept in the paddock
adjacent to the crush from 7.00 till 17-00 hours daily. Cut grass
was supplied to supplement the low amount of grazing that was
possible in that paddock. Water was supplied ad libitum. On the
fifth day (2^th April), 12 heifers (U Brown, U Holstein and 1+ Fulani)
were bled by jugular veni. puncture at 7 -0 0, 1 2^.0 0 and 17 -0 0 hours
as they passed through the crush. Thei- r vr<ehctal temperatures
were recorded.
2: The aim of the second experiment was to see if more 
frequent blood sampling could be done by using few animals. In 
early June, all the experimental heifers were again conditioned as des­
cribed above ^Sross the weighing race and crush frequently 
during the day for about a week, after which (June 9) three 
heifers (Brown 8U, Holstein 1̂ 5 and Fulani 21) were separated 
from the other heifers and bled at 7-30, 1 1 .0 0, 16 .0 0 and 
18 .3 0 hours of the day.
3: In the third experiment, the same procedure as above 
was repeated in late August (25th) when 13 heifers (U Brown,
5 Holstein and U Fulani) were bled at 07.00, 11.00, 15-00 and 
18.30-19.00 hours. Thus, more blood samples were collected in the 
heifers kept in the sun throughout the day than in experiment (1 ).
68
U: The aim of the fourth experiment was to determine
the circadian levels of plasma cortisol in shaded heifers.
Three heifers were restricted by tying to the stanchion in the 
pen for a week during which time they were visited at about 3 - U 
hours intervals during the day and twice in the night, and 
restrained briefly in the posture for jugular blood collection. 
Blood (2 ml) was collected only in the morning (7.30 hour^ as 
part of the conditioning, and was discarded. The heifers were 
bled by jugular venipuncture by 0 7.3 0, 1 5 -0 0, 1 8.0 0, 2 3.000,
01.00 and (A. 30 hours on the 16th of May. The experiment was 
repeated in the middle of September and early October. However, 
in order to diminish the possible effect of restraint on plasma 
cortisol levels, blood was collected from the tail vein on 
these two occasions, making use of heparinised evacuated venoject
tubes (Terumno Corporation, Tokyo, Japan) (Brown 1963;
Ghoshal and Getty 1967). Different heifers were used on each 
occasion and they were tied to the stanchion for a week prior 
to blood collection.
Rectal temperatures were not taken during the subsequent
investigations after experiment 1 so as to avoid prolonged 
handling of the animals, and, to decrease the interval of 
bleeding between the heifers. Heifers were bled under 1 minute
69
of approach or restraint in the crush or pg/j . Only 5 mis
of blood were collected each time, and this was kept cool in iced 
water until the plasma was separated. Plasma samples were 
stored at -20°C till the time they were analysed for cortisol 
concentration by radioimmunoassay. The results were treated 
by analysis of variance, using 'breed' and 'time of the day' 
as sources of variation.
The adrenocorti. cal response to AiCTHf wa.s i nvesti. gated i.n
early January 1977 after all the; quartcerly blood samples had been
collected from the heifers. ^ ^ h eheiifers of each breed in the
diestrous phase of estrous cycle (between days 1  and 10) were
weighed and used for the& investigation. Led by the BN teaser bull, 
they were made to pass the weighing crush at 2 hourly intervals 
from 0 7.0 0 till 16 .00 hours daily for 5 days. After each round, 
the heifers and the bull were kept in a space on one side of the 
passage and crush. This space was compact enough to allow 
driving them out again easily. They were supplied with their
normal feed in that space.
On the si. xth day,t /h eh dfers were bled by j. ugular veni.puncture
at 0 8 .3 0 hours, that is, zero time before the intramuscular
injection of 5 ml of 0.9% physiological saline. After the blood
collection, the same animal was immediately led back to queue
70
behind the other animals in the passage for the second and third 
blood collections. A time interval of about 60 minutes was 
allowed before the Uth to 6th blood collections; thereafter 
the intervals of 2 and 3 hours were allowed for the last two 
blood collections. At the end, it was found that the intervals
rounded up to 0, 30, 30, 80, 65, 60, 120 and 180 minutes. The
heifers were again bled by 0 7.0 0 hours
and the routine of passing through the crush every 2 hours was 
continued. Three days after the saline injection, the heifers 
were injected intramuscularly with 200 I.U ACTH (Porcine,
Sigma Chemical Company, St. Louis, Mo. U.S.A.) dissolved in 5 ml 
physiological saline, and were bled as described above. Blood 
was also collected on the following morning by 0 7.0 0 hours. 
Another 100 I.U. of ACTH was then injected but blood samples were
The same heifer served as her own control. The procedure 
was carried out as quietly and as rapidly as possible with the 
aid of a number of assistants. Five milliliters of blood were 
collected each time into heparinised tubes which were kept in iced
water until centrifuged. The plasma was stored at -20°C until the
time of assay. The result was treated by analysis of variance; 
time after injection, type of treatment and breed were considered 
as separate sources of variation.
71
Observation for estrus and per rectal examination of 
ovaries of experimental heifers were carried out during a period 
of investigation lasting 1̂  calendar months. The attendant 
assisting in the project was taught how to detect estrus.
Other attendants also reported cases of mounting by the bulls.
The BN bull was made to wear a heat detector halter filled with 
a dye on some nights and some week-ends when it was expected 
that regular observations might not be possible. A teaser bull 
was always in each of the two pens occupied by the heifers.
All the experimental animals stayed together in the same paddock
while in the fi. eld in the mojrQniyngs, but they were kept far from 
the other cows and heifers not on experiment so that the teaser 
bulls might not be distracted. Observations for estrual signs normally 
b^gan at 05.0 hours ^  -^e author or any of the attendants.
The special assistant allocated to the project continued the 
observation until 1 5 .30-16 .0 0 hours.
Afternoon workers reported cases of mounting among the heifers 
or by the bulls between 16.00 and 18 .0 0 hours. The author 
mandatorily observed the animals twice daily in the morning and 
in the evening apart from the need to be around for various 
procedures at some other times. Observations for estrus by the 
author in the night between 22.00 and Ol+.OO hours was often 
necessary when heifers showed proestrual signs during the day or
72
when the end of an estrual period was to he recorded.
Estrus was recorded as standing heat (staying to he mounted) 
and suhestrus as slight estrual signs without standing to he mounted. 
The time when a heifer first stayed to he mounted was regarded as 
the onset of estrus. During the four quarters, marks were awarded 
for each animal for the intensity of expressed estrus. Intensity
was graded as high, medium and low, marked (■ (++) and (+)
respectively. In accordance with the method of Hafez (1969), 
estrual intensity was judged by the occurrence of vaginal discharge, 
the expression of certain behaviour including the frequency of 
mounting by the animal, standing to he mounted and restlessness.
To determine the duration of estrus, the heifer on heat was 
allowed to graze with the group in the paddock in the morning, 
and upon returning from the field she was separated into another 
pen away from the teaser hull. The BN hull, or occasionally the 
Fulani hull, was introduced into the pen at intervals of 1 hour.
If estrual signs had commenced at night, the heifer was similarly 
teased, hut the interval of teasing was longer (2-3 hours). At 
times, the heifer on heat was not allowed to graze hut was kept 
in the pen and teased as long as estrus lasted. The time when 
estrus stopped was taken to he the mid-point between the last time 
the heifer stood for mounting by the hull and the next and last 
teasing when the heifer would not stand for mounting.
73
Ovarian examination by rectal palpation was done while the 
heifer was stall-tied or restrained in the crush. Ovaries were 
palpated once at estrus to locate the Graafian follicle. Ovarian 
examination was then repeated at intervals of 6 hours. The time 
when ovulation occurred was estimated as midway between the time 
the Graafian follicle was last observed and the time when an 
ovulation depression was found. In some cases where an ovulation 
depression was palpated during the first examination after the end 
of estrus, the time of ovulation was assumed to be the time of
examination.
Histograms were drawn to show the percentage distribution 
of the time of onset of estrus through the 2b hours of the day, 
the duration of estrus and the length of estrous cycles in 
the different breeds (Figs. 11, 12, 13). The time of onset of 
estrus through the 2lt-hour day was tested by chi square analysis-
and the analysis of variance was used to test the effect of the 
month of the year. The significance of the breed and seasonal, 
differences in the length of estrous cycle, duration of estrus
and ovulation time were determined by employing the student t-
test.
74
Radioinnnunoassay of bovine plasma cortisol 
Introduction
Very few studies involving displacement analysis in estimating 
bovine plasma cortisol have employed specific antibody (Dobson 
and Kanchev, 1977)• This is probably so because of the 
relatively low cost of the "binding protein" employed in 
competitive protein binding assays which have been more commonly
useds or m  some places, the low reproducibility of RIA of cortisol.
RIA ensures greater sensitivity because of the specificity 
of the antibody. Early work on the RIA of plasma cortisol involved
extraction and chromatographic purification (Ruder et al. 1972). 
Other assays have been performed on crude extracts after plasma 
protein precipitation with ethanol because of the greater 
specificity of the antiserum, (Abraham et al. 1972; Farmer and 
Pierce 197*+; Viscei 197*+)- Highly specific antibody to cortisol 
can also be used to assay cortisol directly in very small volumes
of plasma.
Materials and Solutions
Assay tubes were made of pyrex glass (Joblin and Co.) and 
had a di. mensi. on of 12 x 75 mm and/wNririjtmless. Round bottomed tubes 
had a dimension of 100 x 1*+ mm. The tubes were soaked for at
75
least 2k ohurs either in pyroneg (Cockfosters, Barnet, Herts, U.K.) 
or dichromate solution. They were then washed with tap water and 
distilled water. Counting vials were soaked for at least 2k hours 
before washing. Other glasswares were similarly treated. Oxford 
pipettes (Oxford Laboratories, U.K.) with disposable tips were used.
Phosphate buffer stock solution was made up of 17-̂  gm of
disodium hydrogen orthophosphate anhydrous 1U2), (Na^HPOU),
10.8 gm of sodium phosphate (NaH^POU) (M.SW.? 138), 2.0 gm of 
sodium azide (NaN̂ ), I8.0gm of sodium chloride ($aCl) in 2 litres. 
The buffer had a pH of 7 and was stored at room temperature.
The assay buffer contained an additional 0.1% gelatin and 
was stored at 1+°C.
Won-radioactive cortisol standard (Sigma Chemical Company) 
obtained in vials containing 50 pg/vial was diluted without 
further purification with absolute ethanol to a concentration of 
20 ug/ml which was stored at -15°C as stock solution I. From 
this solution, stock solution II containing 1 ug of cortisol/ml 
ethanol was prepared and stored at -15°C. Different volumes of 
stock solution II, that is, 100 ul, 50 ul, 20 ul, and 10 ul 
were dried down in vials labelled A, B, C, D, respectively. The 
residues were dissolved in 10 ml phosphate buffer (pH 7) by
placing the vials in a 30 C water bath for 10 minutes and
76
subsequently mixed on the vortex mixer (Vortex-Genie, 
Scientific Industries Inc. Springfield, Mass.) for 15 seconds.
5.0 ml of solution in vial D was transferred to another vial E 
to which 5 ml of phosphate buffer was added. In this way, 
standard solutions A to E were prepared containing, 5,000,
2 ,500, 1,000, and 500 and 250 pg per 0.5 ml phosphate buffer 
respectively.
(1, 2, 6, 7(n) - OH)-cortisol with^specific activity of
85 Ci/m mol (Radiochemical Centre, Amersham, England) was purchased 
in vials containing 250 juCi each. The content of each vial was 
diluted to 5 ml with benzene-methanol (9:1) solution and stored
at 1°C. About 20 juCi was purified each time by Sephadex LH-20 
column chromatography (30 cm x 1 cm) using solvent system
Solution was made up in phosphate buffer just before the assay and 
contained approximately 5,000 cpm/100 ul.
Lyophylised antiserum to cortisol (Batch S-69^ 3 ) was obtained 
from Dr. G. E. Abraham, Harbour General Hospital, Torrance, 
California 90509, U.S.A. The antiserum had been raised in rabbit 
against Cortisol-21-hemisuccinate-Human serum albumin.  ̂The cross 
reactivity of the antiserum with some plasma steroids are as follows
77
Corticosterone 31$, progesterone 5$ , 17-hydroxyprogesterone 6$, 
aldosterone 0.7$, estradiol-17/3' '0.12$, estradiol-1 Toe 0.12$ and 
testosterone 2$ ). Aliquots of the antiserum were diluted with 
distilled deionised water, and kept frozen at -20°C. An aliquot 
of the stored dilution was thawed before use and diluted with 
phosphate buffer solution to the working dilution. The final 
dilution chosen was that which bound betwee of 5,000 cpm
of (^H)-Cortisol, and this was between * 000 and 1:1*8,000.
The fine particles in Norit A (activated charcoal) were 
removed by soaking in methanol overnight and filtering with
ordinary filter paper to which the particles adhered. 0.625 gm of 
dry charcoal with 0.0625 gm Dextran T.70 made up to 100 ml in assay 
buffer was prepared to last 2 to 3 days.
The scintillation fluid was made up of toluene (Fisher 
Scientific Company, New Jersey, U.S.) containing 5 gm per litre 
of 2-5-Diphenyl oxazole (PP0) (BDH Chemicals Ltd. Poole, England),
0.1 gm/litre of 1-l+-bis(2(U-methyl-5-phenyl-oxazolyl) benzene 
(POP0F) (Sigman Chemical Company, St. Louis, Missouri, U.S.).
This was mixed in a ratio of 2:1 with triton X-100 (BDH Poole, 
England). The fluid dissolved aqueous solutions satisfactorily.
78
Preparation of Samples
0.1 to 0.2 nl of plasma was taken in duplicate round-bottomed 
tubes, and 3 ml diethyl ether was added and mixed on the vortex 
mixer for 1 minute. The aqueous layer was frozen by keeping the 
tubes at -60°C for 10 minutes; the ether layer was quickly 
decanted into labelled assay tubes and evaporated at Uo°C or
at room temperature overnight. To each tube was then added 
0.5ml of the assay buffer. All the assay tubes were then heated 
in the water bath at 60 C for 10 minutes and then mixed for 
30 seconds on the vortex mixer. Deionised distilled water 
served as a blank (BK) in duplicate tubes. Two solutions of 
non-radioactive cortisol containing 10 ng and 5 ng/ml of 
deionised distilled water in duplicate tubes labelled 'R10' 
and 'R5' respectively, and bovine pooled plasma in duplicate 
tubes labelled ’P* were also treated like the plasma samples.
The Assa;
For the standard curve, assay tubes were arranged in triplicates
and labelled N, B°, T, A, B, C. D, E. "N" represented 'charcoal
resi• dual', that i. s, the amount of ( 3H)-cortisol not removed by
charcoal during adsorption process'Bo' represented maximal 
binding by the antiserum at zero concentration of non-radioactive 
hormones; 'T' represented total radioactivity added to tube 'T'
79
and to al1 other tubes, A to E are the decreasing concentrations
of standard non-radioactive steroid.
The working solutions of antiserum and ( H)-cortisol were 
prepared just before the assay was performed and equal volumes of 
the two solutions were mixed. 200 pi of the mixture was added
to tubes 'Bo*, 'A' to 1E*, the ’sample' tubes, and tubes 'BK',
'R̂ ' and 'P'. 100 pi of the workin^g ^sLouluttiion of ( n)-cortisol
and 600 ul of distilled deionised water were added to tubes 'N' 
and 'T' only. 500 jul of the non-radioactive cortisol standard 
preparations in vials A to E were added to the corresponding assay 
tubes 'A' to 'E'. To tubeiBo'was also added 500 pi of the assay buffer.
The tubes were incubated at 60°C for 10 minutes and then 
at 30°C for 2-3 hours. They were then cooled in ice water (U0C) 
for a minimum o inutes. 0.5 ml of the charcoal suspension was
added to all tubes except 'T'. The racks were shaken from time to 
time during the charcoal adsorption process to make the. suspension
homogenous. After 10 minutes, the tubes were centrifuged at k°C
_ *
and at 3,000 rpm for 10 minutes. The supernatants were collected 
in vials to which were added 5 ml of scintillation fluid. Counting 
was for 2 minutes per vial in a Packard ^-Scintillation automatic 
counter model 3390, the efficiency of which was 60% for tritium.
80
Calculations
The 'charcoal residual' (N) count was subtracted from all 
counts except 'T'. The binding percentage was calculated as Bo/T x 100. 
This gave values ranging from 25-37$ throughout the assays. The
binding in tube Bo*was taken as maximal or 100$ binding and the
binding (B) in all other tubes (Standards A-E, Bk, R5, R10, P and samples]
were calculated as percentages of 'Bo* (i.e For the
standards, the logit transformation of the percent bound was plotted 
against the decadic logarithm of concentration as proposed by 
Rodbard et al (1968); and a linearised curve was obtained. The 
logits for the percent bound in the samples were found and the cort'Sc 
concentrations read from the graph. A hand calculator, Hewlett 
Packard HP-25, was programmed for regression analysis; the 
logarithm of concentration was plotted against the logit. A 
fast calculation was obtained by using this device (Cekan 1976). 
Assay values were corrected for recovery by multiplying with the
yield factor and were expressed in nanograms/ml. Experiments to 
determine the reliability of the assay procedures are reported 
in the appendix.
81
RESULTS AND DISCUSSIONS
I * Physiological responses 
Respiratory rates
Mean respiratory rates in the heifers during each quarter 
are shown in tables 1 and A12. The result of analysis of 
variance (tables A 13 and A 14) .Shows that the effect of season, 
breed and time of the day were individually significant (P< 0.05,
P<0.05 and ?< 0.01 respectively). There w<as pno significant 
(P> 0.05) interaction between the season, breed and time of the day 
effects. From the analysis of variance, season, breed and time of 
the day contributed well to the total variations that occurred (table
A 14). The respiratory rates both in the morning (7 - 7.30 hr) 
and the afternoon (13 - 15.00 hrs) were significantly (P^ 0.05) 
higher in the Holstein than in the Brown which also has significantly 
higher (P<0.05) readings than in the Fulani.
Mean respiratory rates varied between the different periods 
of the year with highest afternoon readings occurring in the dry 
hot months of November through April and the lowest in the wet 
months of July and August. Lowest afternoon readings during the 
dry season were recorded in December and early January. Higher 
morning respiratory rates were obtained during November through 
April than in July - August; the values in the mornings in March - 
April were higher than other periods in the dry season. See figure 7.
82
The percentage change of respiratory rates in the afternoon 
over the morning low valued Jjs shown in table II. There was a 
significant (P<0.05) difference between the morning and afternoon 
respiratory rates as shown by the analysis of variance. The dif­
ference was less marked in July - August. Panting was exhibited 
by the Holstein heifers on hot afternoons most especially in the 
sun before they were brought into the pen.
Rectal temperature
The mean rectal temperatures of the hei&fers are shown in
tables III and A 15. The analysis of vaf^Shce (table A 16) shows
that the main effects, season, breed and time were individually 
significant (P<0.01). Significant (P< 0.01) interactions that 
occurred were between season and breed and between season and time 
of day. Time of the day effect contributed most significantly 
to- -the t0ta,l variation that dccurtfed (Table A 17) .
Seasonal differences were more- noticeable in the afternoon 
rectal temperatures the values being significantly lower in 
July - August than in other periods (Table III) . There was a 
small relative rise in the morning rectal temperature in March/April 
over the values in Deceraber/January. See Fig 7 for seasonal values 
in the physiological responses.
DiurnaL changes in rectal temperature were most impressive 
than seasonal changes. Differences between morning and afternoon
83
temperatures were higher in November through April than in
July - August, Highest diurnal changes were obtained in November.
On many days in the July - August period there was little difference 
(< 1°F) between the morning and afternoon rectal temperatures* Both 
morning and afternoon rectal temperatures were generally lower in the 
Fulani than in the temperate breeds. Mean afternoon rectal 
temperatures were generally higher in the Holstein than in the Brown
heifers though the difference was not signi (P> 0.05). On
some hot afternoons fairly high shade temperature 103 - 104 F (39.4 - 
40°C) , 103.5f(39.5°C), and 103T(39.4°C) were recorded in the Holstein, 
Brown and Fulani respectively recurring most often in the Holstein 
than in the Brown or Fulani heifers and very infrequently in the 
Fulani.
Rectal temperature did not show any rhythmicity through the 
estrous cycle. Occasionally in some animals, rectal temperatures in 
the morning of the day of estrus resembled the usual afternoon values, 
that is, about 102°F or more; this may not be obvious in a composite 
graph since at other times the values were low (Fig. 8). Elevations
were more frequent in the afternoon of the day of estrus when the
as 0
values might be as high/103 F. The value on the day of ovulation was 
not depressed below usual levels.
Shade seeking
The Fulani heifers did not seek shade throughout the periods 
of observation (Fig. 9). The result of analysis of variance (table
84
A 18) ot- the scores of shade seeking in the Holstein and Brown heifers 
(table A 19) shows separates' significant- breed .(P. <-’t).Ql) and season 
' (P i  0.05) effects. Heifers of both temperate breeds sought shade during 
all periods of the year but the frequency was higher in the Holstein. 
The percentage scores ranged between 80 and 100 and between 20 and 
60 in the Holstein and Brown heifers respectively during the hotter
more sunny periods (November
10 and 20 in the same order o he
established hierarchical order was brought to play in occupying 
shaded areas and animals with higher rank often displaced those with 
lower rank. Generally the Brown heifers easily displaced the
Holstein heifers.
The grazing of the heifers was not disturbed and there was no 
breed difference in the cool weather and especially when cloud cover
was considerable. On sunny cloudless hot days, when grazing in the 
paddock having tree shader the grazing time of the Holstein heifers 
lasted about 10 - 20 minutes at a stretch and about 20 - 35 minutes 
for the Brown.
The animals might move into or out of the shade depending on 
whether the sunshine was still intense or had reduced due to a 
temporary cloud cover. When no shade was available in the paddock,
the reaction of a Hostein heifer might just be to stop grazing and to 
stand on one spot, panting. Individual differences occurred in 
grazing behaviour as some heifers of the same breed stayed longer
85
than others. Generally the shade seekers did not graze far from the 
shade. The grazing behaviour of the Fulani heifers was apparently not 
affected by solar radiation, as they grazed continuously in the sun, 
covering wide areas.
Only the Holstein heifers exhibited panting behaviour among the 
breeds. This behaviour was shown mostly in the fieldA e.ither in thesun or in the shade. The typical panting heifers (Fig. 10) stopped 
grazing, the head was lowered, the mouth opened and there was profuse loss
of saliva as well as some nasal discharge . pypn<za was about 120
breaths per minute and above. The rectal temperature of panting 
heifer was always abnormal, ranging from 104 - 107 F (40 - 41.6 C) . 
Upon getting into the pen polypn&a and hyperthermia subsided after
about two to four hours. &
Discussion
Despite the significant differences in the values obtained in 
the different periods of observation, the mean rectal temperature
responses were within the normal range in the heifers. Both respiratory 
and rectal temperature responses suggest that the heifers were more 
comfortable during July - August period than during the rest of the 
year.
The physiological responses are a reflection of the magnitude 
of heat load suffered by the animals during the different seasons. 
Factors which contribute to the amount of heat load experienced by 
cattle in Nigeria include solar radiation, environmental temperature
86
and humidity, the geographical and seasonal distribution of which 
are, in turn, influenced by the south westerly winds (Ojo 1973) .
The amount of solar radiation reaching the ground surface is 
dependent on the amount of cloud cover during different periods of 
the year. During the July - August period and some other wet months, 
because the inter-tropical convergence zone (ITCZ) has moved far up 
over West Africa, much of Nigeria is under the southwesterly winds 
with the associated heavy cloud cover which limits incoming radiation .
Lower direct and indirect solar radiation, therefore, reach the
animals. The reverse situation occurring in the dry season when ITCZ
moves down to the coastal area brings the country under the dry north eas ter I
winds and the influence of the cloud cover is absent. Since
the heifers were outdoors till 11.00 hours or just after, the influence 
of solar radiation in evoking physiological responses and imposing 
heat load can not be overlooked. Generally, less sunshine occurred 
before 11:00 hour in July - August or during the wet cooler months 
compared to other periods of the year, especially, November through 
April. A recent report (Romance-Pounce et al 1977) and a part of 
this present investigation show that responses are greater in 
unshaded than shaded cattle. Sufficient heat load might have been 
gained by the heifers outdoors before they were moved into the pen
and this might have influenced their afternoon rectal temperatures.
87
The relatively low environmental temperature occurring in 
July - August (maximum ET °ranging between 76 and 85°F) (24.4 - 29.4°C)
possibly increased the temperature difference between the body and the 
environment. More heat was, therefore, lost to the environment 
through radiation and convection. Hence less heat load might have 
occurred during July - August (Ojo 1973). By the same token, higher 
environmental temperature in the hot dry season would mean generally 
more heat load and higher physiological responses. The air
temperature was however not higher than thiee beody temperature; and 
there was, therefore, probably no convectional heating from the wind. 
The higher humidity prevalent in July - August would be
expected to interfere3 with the esvap<orative heat loss and thus
impose some heat load and evoke high physiological responses during
that period. The observed responses in the present study show that 
the effect of high humidity was not as stressful as expected. This 
can be explained by the work of McLean and Calvert (1972). They 
showed that surface evaporative moisture loss was not disturbed by 
moderately high humidities at high temperatures because of a 
continuous process of reestablishment of new vapour pressure gradients 
between the skin surface and the surrounding air when the vapour 
pressure of the air was increased. Moreover, in the field, the 
influence of the wind in the micro-climate, in disturbing 
continuously the vapour pressure gradient can further cause 
increased evaporative moisture and, therefore, heat loss.
88
Ojo (1973) in his report on the possible effect of the environment 
on cattle in Nigeria, showed that evaporative power of air and 
consequently evaporative heat loss is reduced in July in areas where 
high humidities combine with environmental temperatures higher than 
80 - 85°f (26 - 29.4°C) especially in the middle belt of the country.
The Ibadan area to the south is not so affected, the maximum air 
temperature during July - August period 76 - 85°F (24.4 - 29.4°C)
being relatively low. Kibler and Brody (1 reported that rectal
temperatures of cattle do not rise at environmental temperatures 
below 70 - 80°F (21.1 - 26.6°C). The closeness of this range to the 
values obtained in Ibadan area during July - August may also explain 
the lower diurnal changes in rectal temperatures in the heifers at 
that time. The influence of exercise in the field and at times in 
the pan might, however, exaggerate the rectal temperature changes.
Seasonal variation in rectal temperature reported in the 
heifers in this study is not in agreement with the report by Wolff 
and Monty Jr. (1974) who found no such seasonal differences in the 
rectal temperature in non-lactating cows. In that report, only the 
lowest morning and highest afternoon temperatures were considered.
On the other hand, the rectal temperatures considered in this present 
report were obtained at definite or specific times of the day, (at 
07 - 08.00 and at 14 - 16.00 hours) and not necessarily the lowest 
or highest possible, respectively, in the day. There is a greater
89
tendency to obtain uniform results when only the minimum or maximum 
values of the morning and afternoon respectively are considered than 
when values at a specific time of day are considered for very many 
days.
The seasonal differences in rectal temperature were, howeverr 
not great. The depression in the mean values in July - August was 
small. The only significant feature was that lower afternoon rectal 
temperatures were recorded during that period of the year than in 
the dry hot season. The fact that the animals were not under lacta- 
txonal stress must have contributed to the relatively low seasonal 
variation in the rectal temperatures, since milking cows have been
found to respond markedly to seasonal weaalther conditions (Berman
& Morag 1970; Wolff & Monty, Jr. 1974). Secondly, the fact that the
heifers were under shade (in the pen) for a greater period of the
24 hour-day (between 11.00 till 07:300 hours) must have caused the
relatively little seasonal differences in the rectal temperatures.
Cows in the shade have been found to show lower rectal temperatures
^^the
than those not in/shade (Rainey et al 1967; Romance-Pounce et al
1977).
The higher morning rectal temperature in the rainy season may 
reflect an increase in body heat production due to increased metabolic 
rate. The commencement of the rains and the associated increase in 
available pasture and therefore ingested material might have caused an 
increase in metabolic rate. Increased feeding has been associated
90
with higher metabolic rate (Robinson & Lee 1947; Rogerson 1966;
McDowell ct al 1955; Ingraham and Whittow 1961).
It is also possible that the lower rectal temperatures in 
December/January were partly due to the cold mornings. Moran (1970) 
found positive correlation between the rectal temperatures and dry bulb 
temperatures and believed that the varying morning air temperatures 
influenced the rectal temperatures. Howes et al (I960) also found 
that cold mornings depressed vaginal temperatures of cattle.
Breed differences in rectal temperature observed in the 
heifers also agree with some previous reports (Romance-Pounce 
et al 1976? Sheath and Miller 1947). The lower mean morning rectal 
temperatures in the Fulani as against the Brown and Holstein could be 
of thermoregulatory advantage permitting the Fulani to experience 
greater increases in body temperatures without becoming hyperthermic.
t
Previous studies have also discussed the thermoregulatory advantage 
of low morning temperatures (Bianca 1959a, 1959b). Bianca(1959b) 
reported that rectal temperatures were lower in acclimatized than 
in non-acclimatized zebu calves. Hutchinson and Mabon (1954) also 
found that zebu cattle reared under temperate conditions had lower 
rectal temperatures in summer than in winter months. Similarly non- 
lactating dairy cows had been found to show lower morning rectal 
temperatures during the hot season than during the cool season 
(Wolff and Monty Jr. 1974).
91
The generally low morning rectal temperatures in all the heifers 
in December - January including November in the Fulani and the Brown 
may be of similar thermoregulatory advantage by delaying the onset of 
hyperthermia as also suggested by Bianca (1959b). It may also be 
signifying a reduction in the metabolic rate in the animals during 
the dry season.
I h€ amplitudes of the respiratory responses were more 
obvious and pronounced than rectal temperatures both diurnally and 
seasonally. Earlier reports have also shown that respiratory rates 
in calves and cows wtye more sensit:iivve to h<e at stress than the rectal
temperature (Bligh 1957; Rj ek & Letee 1948) .. The high respiratory
responses in November through April is probably due to the generally 
poor ability of the body to eliminate heat through the skin.
The sensitivity of the respiratory responses to environmental 
temperature changes was demonstrated by the distinct values obtained 
during the different quarters, thus indicating the severity of thermal 
stress during each period similar to the report on non-lactating 
and lactating cows (Wolff and Monty Jr. 1974-- Berman & Morag 1970) .
The generally higher morning respiratory rates in March - April might 
be associated with higher morning environmental temperatures which 
increased more rapidly during that time than at any other period of
the year.
92
The high sensitivity of the respiratory responses to environ­
mental heat is due to the sensitivity of the peripheral and central 
thermoreceptors which set up impulses that initiate polypnea 
(Findlay and Ingraham 1961; Ingraham & Whittow 1962 ) ,
Because of its high sensitivity to environmental heat, respiratory 
response has been described as an anticipatory defence mechanism 
preventing the rise in core temperature and delaying the onset
of hyperthermia (Bligh 1957). The high respiratory raesponses m
the Holstein heifers under shade (in the pen) were not necessarily 
associated with abnormal rectal temperatures. The heifers were
therefore maintaining relatively normal to low hyperthermia in the
hot weather at the expense of gr ieat& :espiratory effort.
The breed differences i.n respiratory responses may bg ;reflecting the
differences in cutaneous ev4a p^orative heat loss including the extent 
to which the coat characteristics prevented heat gain or interferred
with heat loss. The advantage of a light coat in aiding heat tolerance 
is derived from its being able to absorb less heat and reflect more
visible radiation than brown and black coats respectively (Riemerschmir 
1943; Bonsma 1943; Bonsma and Louw 1963). The texture of the short and 
medullated zebu hair further aids evaporative heat loss and has there­
fore been associated with increased heat tolerance (Hayman & Nay 1961). 
This attribute of the zebu coat has also been described in the Fulani
cattle (Hill 1960; Amakiri 1974). The coat type advantage must have
93
contributed to the greater heat tolerance in the Fulani over the Brown 
and Holstein, A greater inadequacy of the sweating mechanism in the 
Holsteins as against the Brown and the Fulani is also suggested.
The breed differences in shade seeking habit signify obvious 
differences in heat tolerance. It also suggests that the efficiencies 
of the evaporative heat loss mechanism and of the coat type in 
preventing heat load differed between the Fulani, Brown and Holstein 
heifers decreasing in that order of breeds. Sheath and Miller (1947) 
and Romance-Pounce et al (1977) have also described the shade-seeking 
habit in Holstein cattle which, in addition, frequented and lay in wet 
places. This has been related to low heat tolerance in this breed 
(Sheath and Miller 1947). The species difference in shade seeking 
shows the superiority of the Fulani over the temperate types of cattle
in heat tolerance.
Hafez (1964) described shade seeking habit as a physical 
voluntary behaviour of thermoregulation in homeothermic animals 
seeking micro-climate in the ambient temperature. In this present 
observation, the animals sought shade from direct solar radiation and 
not from ambient temperature. The behaviour of the shade seeking 
heifers shows that the direct solar radiation is capable of causing
rapid increases in body temperature. Voluntary behavioural responses 
to heat might be controlled by the central nervous system (CMS) (Johnson 
et al 1962; Hammel et al I960). It is possible that impulses set up
94
at the thermoreceptors in the skin by the solar radiation as well 
as at the central thermoreceptors in the anterior hypothalamus due 
to increased blood temperature initiate motor responses in the 
CNS causing a withdrawal from the sun into the shade.
The lower frequency of shade seeking during the July - August 
cooler wet period was due to less sunshine as a result of a more 
extensive cloud cover. The grazing behaviour was closely related 
to the shade seeking behaviour. Since shade seeking behaviour 
commenced at any time from 10.00 hours depending on the severity 
of incoming insolation, the grazing time of the Holsteins was 
markedly affected and the total amount of feed consumed could be 
highly reduced by the long peri o & U  in the shade. Seath and 
Miller (1946) similarly found that solar radiation with high 
ambient temperature depressed grazing time. Since the animals 
moved out of the shade to graze when clouds temporarily prevented 
direct solar radiation, the appetite of the heifers was probably not 
depressed by the environmental heat, although there are reports 
from studies in the laboratory that feed intake is depressed by 
high environmental temperatures up to 29 or 30°fc in both non-heat 
tolerant and heat tolerant cattle (Johnson et al 1967? Holder I960).
The Fulani cattle in their natural environment, are grazed 
over wide areas in the savannah bush. The dairy stock of this breed 
from which the experimental heifers for this study were obtained
%
95
are also normally grazed over wide areas on the university campus 
and farm from morning till about 15s30 hours after which they were 
left outdoors in the paddock close to the milking barn. The 
ability of the Fulani heifers involved in the present study, to 
graze for long periods in the sun is therefore typical of the breed.
The ineffectiveness of panting in reducing body temperature 
is evidenced by the fact that panting heifers showed hyperthermia
in the field. Panting might in fact increase heat production
(Thompson 1973). The fact that the Brown anAd Fulani heifers did 
not pant shows that they possess greater heat tolerance than the 
Holstein heifers. There are indiciatpions that peripheral thermo-
receptors in response to ambient temperature, infra-red irradiation, 
and heating cause marked increases in respiratory rate (Bligh 
1957) Findlay & Ingraham 1961). In the present study, the combined 
effect of high ambient temperature and solar radiation can be
implicated as the cause of panting. A probable poorer thermolytic 
ability of the Holstein might have caused the observed high body 
temperature while grazing on the field and this hyperthermia might 
have further exacerbated panting by stimulating the hypothalamic 
thermoreceptors. The opened mouth during panting is probably due to 
increased respiratory tidal volume. The loss of saliva was due to 
the normal continuous parotid gland secretion, finding an outlet in
96
the opened mouth. This fluid loss may play some role in heat loss, 
the magnitude of which is however not known.
Amakiri (1974) found that Holsteins in the Ibadan environment 
have developed sweat gland characteristics (including increased sweat 
gland population) suggestive of increased heat tolerance. The 
physiological responses observed in this present study do not
suggest greater heat tolerance in the Holstein th8^ the Fulani
heifers. It is however possible that the large number of sweat glands 
developed in the adapted Holsteins are not as efficient as those in
the Fulani cattle. If the greater surface area per unit weight
which Kibler and Brody (1950) found for the Brahman (zebu) cattle
over the Holstein is true for the' F2u?la™ni over the Holstein, the Holstein 
heifers would be suffering the disadvantage of a relatively lower
cutaneous evaporative surface area. This^ coupled with the poorer
influence of the coat type in preventing heat gain and aiding heat loss, 
may be overshadowing whatever advantage may be conferred by the 
improved sweat gland characteristics.
Generally, however, the Bos taurus breeds seem to be able to 
adjust to the changing seasonal weather conditions. The major 
indication of breed differences in heat tolerance or in the effort 
of adjustment to the seasons, when the animals were shaded, was the 
respiratory rate. The large seasonal shifts in respiratory rates in 
the temperate breeds as well as the relatively normal body temperatures
97
under high environmental temperatures shows that to a large extent 
these animals have large capacity to withstand heat under natural 
tropical climate, especially if shade is provided. The occurrence of
occasional hyperthermia in the shade particularly in some H'olstein 
heifers is a poor prognosis for the heat tolerance of these animals 
at lactational age.
As regards the relationship of rectal temperatures to the 
different stages of the estrous cycle, the elevation of body 
temperature on some mornings of the day of estrus is not well 
reflected in the composite graph, because oJf the more commonly
recorded normal temperatures at that time. This is probably so
because animals at estrus can exercis5e less in the pen than in the 
paddock. The more commonly recorded elevated temperature in the 
afternoon of the day of estrus was, therefore, probably due to the 
increased activity associated with estrus while the animal was in 
the field.
The present results disagree with some previous reports showing 
an occurrence of definite cyclic pattern in the body temperatures 
(Vollan & Vollan 1942; Bane & Rajakoski 1961; Wrenn et al 1958). The 
distinct depression in the body temperature on day 2 of the cycle 
coinciding with ovulation, reported by these workers and by Smirnova 
(1954) was not observed in the present study. The elevation in rectal 
temperature on the day of estrus observed in the present study agrees 
with previous reports. It has been suggested that the cyclic pattern
98
in vaginal or rectal temperature during estrous cycle is due to the 
effect of circulating progesterone and therefore the activity of 
the corpus luteuro (Bane & Rajakoski 1961? Wrenn et al 1958).
Howes et al (1960) found little evidence of diphasic shift 
in vaginal temperature Of cattle and suggested that the effect of 
environmental temperature can alter the pattern of the cyclic vaginal 
temperature changes, since they found that cold mornings also depressed 
vaginal temperatures particularly in Indian cattle (Zebu). The 
environmental background for the study conducted by Wrenn et al (1958)
was not given. They obtained a diphasic paJtvtern in 90 per cent of the 
dairy cattle they investigated. To obtain this percentage, the 
animals must have possibly been maintained under uniform conditions in 
a closed barn, and not exposed to the field as has been done in the 
present study and in that conducted by Howes et al (1960).
This test, as applied in humans, perhaps because of the better 
controlled conditions is more satisfactory than in cattle. Even then 
in humans, the basal body temperature has been shown to be of very 
limited value in fertility studies and an unreliable indicator of the 
time of ovulation (Siegler and Siegler 1951).
The lack of definite diphasic pattern in the rectal temperature 
of heifers in the present study shows that the influence of ambient 
factors including management on body temperature overshadows whatever 
effect circulating progesterone might have. Since in practical dairy
99
management exercise of cattle in the field can not be avoided, it 
is not likely that the diphasic change in rectal temperature during 
estrous cycle would be of any diagnostic value for reproductive
*:''‘-.P-• ’' r '■p ? ;; ■ ; : v .
biologists working with heifers in the field.
100
11 • Estrous'-cycles in heifers
Result:
(A) Pubertal age
The average age at which heifers of the Brown, Holstein and 
Fulani breeds reached puberty in months were 17.8 (range 16 - 20),
16.7 (range 14 - 19) and 20.3 (range 20 - 25) respectively, The breed
difference was significant between the Holstein and Fulani (table IV). 
(B) Estrual signs . ..................
The sign most often noticed was tail raising as described by 
Hammond ("1927 )and Hafez et al (1969). Rapid switching of the tail also 
described by the same authors as masturbatory rubbing of the perineum 
was noticed on very few occasions (Figs. 27 and 28).
Vaginal discharge occurred in all cases but was not commonly 
hanging from the vulva. Some times it was smeared on the buttocks 
and root of the tail. Intra-rectal manipulations as in ovarian exami* 
nation at suspected or expressed estrus caused copious discharge of 
thin clear mucus through the vulva. This was used to detect some 
heifers showing subestrus especially when the bull’s interest was net 
consistent. The discharge which was clear mucus sometimes also 
contained white flocculus, commonly in the Holsteins but less 
frequently in the Browns, on the day of estrus, and was blood tinged 
on the day after estrus. No growth of pathogenic microbes was observed
101
when the discharge containing white flocculus was cultured. The 
phenomenon was therefore not pathological. The flocculus was not 
noticed in the vaginal discharge of the Fulani heifers. The appearance 
of dry vaginal mucus was not examined.
The congestion of the vulva during estrus was noticed in only 
one heifer (B84) and not consistently. There was no obvious gross 
difference between the appearance of the vulva at estrus and diestrus, 
unlike previous reports (Ilafez et al 1969) .
Frcan marks awarded for intensity of estrus (Table A 20) the 
Brown and Holstein scored higher than the Fulani heifers. Estrous 
intensity ranged from low to high in all the heifers and showed 
individual variations. The intensity was generally high in the 
morning and sometimes late in the evenings but low in the afternoon.
It was also highest at the commencement of estrus. Intensity of 
estrus did not seem to have any relationship with the duration of 
estrus: a heifer showing low estrous intensity might remain on heat
S T
for as long as 20 hours or more. The intensity generally was more 
related to the weather of the day rather than the season, Estrus of low 
or high intensity could, therefore, occur in the wet and in the dry 
seasons..
Mounting behaviour, one of the attributes of estrus intensity, 
was exhibited more by the Brown and the Holstein and least by the 
Fulani. Mounting was influenced by the hierarchical order established:
102
the Browns were highest in the order, and they mounted more heifers 
in the group. Heifers in the low rank of the order mounted few or no 
animals since they were repulsed. Estrus however enboldened the heifers 
in the lower rank to approach and attempt mounting the heifer in the 
higher rank which they would have normally avoided. The mounting 
activity in the Fulani was in many cases nothing more than briefly
raising of the fore legs from the ground. One Fulani (F23) however
exhi. bi. ted as much mounting as the temperate brJeedts*. Placing of the 
jaw on the back of another heifer was most common with the Fulani,
A heifer at estrus exhibited general excitement and restlessness 
as described by Hammond '1927), Hafez et al 1969^ Williamson et al
(l972j). She paced up and down in the pen and disturbed other females. 
Bellowing was not a common behaviour at estrus. Increased restlessness 
was noticeable in the Fulani which might also become unusually playful 
or troublesome in the pen, using her head to push weaker females or 
any female attemptiner to mount her.
The heifer on heat, when released into the paddock in the morning, 
did not graze but concentrated on mounting. Later she only inter­
rupted grazing with mounting. She also accepted the bull frequently.
As solar heat become more intense, the animal showed less interest in 
mounting and might go to the shade. Estrual behaviour might,therefore, 
stop temporarily.
103
A group of heifers often stayed around the heifer at estrus to 
mount her; and during this time she also mounted them. The bull attempted 
to disperse such other heifers. Only rarely was the Fulani in such 
a group except when another Fulani was on heat. Usually too, there 
was also one more dominant (B 84) or more "sexy** heifer (H 137, B 84) 
in the group that was always around to mount the heifer at estrus 
pushing other heifers out of the way.
Subestrus was noticed in a total of three he: 3 and on five
occasions: H 13 and B 87 in February, H 13 xn June, and B 84 in
November of the same year. In subestrus, estrual behaviour was slight, 
or absent and estrus was only detected by the bull, although the 
bull showed only little intermittent interest in such a heifer.
Estrus was confirmed by vaginal discharge on rectal manipulations.
The BN bull was more active than the WF bull. The BN bull was 
also more docile and easily led and amenable to training than the more 
sluggish WF bull. Most of the teasing of heifers was done by the BN 
Bull which dominated over the WF bull. Although the latter had low 
libido at the start of the experiment, he improved with time.
The presence of the teaser bulls seemed to aid the intensity 
of estrus exhibited since the heifer on estrus suddenly became more 
active when the teaser bull was introduced to her. The bull's 
interest in the heifer at estrus was diminished when hungry, after 
many services, or on hot afternoons. The bulls also showed preference
104
for one heifer or the other when two heifers were on heat simulta­
neously. A cow on heat was preferred by the BN bull to a heifer on 
heat at the same time.
The use of a halter with marker was sometimes misleading as the 
bull rubbed the paint on the body of many heifers, resented wearing 
it for a long time and some times forcibly removed it. The BN bull
mounted more frequently and teased less at the commen>cement of estrus 
in a heifer than later during the estrous peri The W  bull 
did not tease when the BN bull was around but went straight to 
mount, in fear of being prevented by the latter. The BN bull was
also more preferred by the ..heifers
Time of onset of estrus
A twenty-four hour distribution of the time of onset of estrus 
was found in the three breeds as has been represented graphically 
(Figure II)* The chi square test showed that there was no breed 
difference in the time of onset of estrus, chi square factor being 
3.045 at 6 degrees of freedom. The highest percentage 41-48%
(tables"V &A21) occurred in the morning between 07.00 and 12.00 hours, 
followed by early morning period 01-07 h . (30.6-38.57%). Few 
estrous periods commenced in the afternoon till midnight. The times 
most favoured were between 0.5.0 and 10.00 hours in the morning. The 
release of the heifers into the paddock in the morning particularly 
seemed to trigger the commencement of mounting activity and standing
estrus
105
The analysis of variance of scores through the months of the 
year (Table A 22) showed that the effect of month on the time of 
commencement of estrus tya$ not significant (P> 0,05) . Breed effect 
was also not significant but the time of the day was highly significant
(P< 0.01) .
Duration of estrus
The percentage distribution of the durat_i_o_n< osf2 erstrus is 
represented graphically (Fig. 12). The histogrraam for each breed 
is flat. For the Browns, the graph shows that the largest number 
of estrous periods (54.6%) lasted 15 - 16.00 hours. A few very long 
estrous periods lasting 27 - 31 hours occurred in some heifers 
occasionally but most often in B 84. Estrus as long as 30 - 31 
hours constitute outliers of the graph. 57% of estrus in the
Holsteins lasted from 11 -j C16K hours, the 13 - 14-hour durations being
more favoured. Outlier&s also occurred on the graph due to a few estrous
periods lasting 29 - 30 hours. As for the Fulani, most estrus (47.5%)
lasted 9 - 1 4  hours. The graph shows a lower flat level after the 
14-hour duration due to some estrous periods lasting between 15 - 24
hours. Some outliers also occurred which are 8 estrous periods lasting 
27 - 30 hours. The mean durationSof estrus were 16.6 (+5.95 S.D.),
15.9 (+5.6 S.D.) and 14.5 (+6.3 S.D.) for the Browns, Holstein and 
Fulani heifers respectively (Table VI )• The difference between
106
the Browns and the Holsteins was not statistically significant 
(P^ 0.05); but the difference between the Fulani and the Brown 
(table VII) was statistically significant (P^'0.05). Longer estrous 
periods were recorded in the wet season (March through October) than 
in the dry season (November through February); the difference was 
not statistically significant (P^ 0.05) (tables VIII and A 23).
Most estrus ended between afternoon and night. Rer,l at.ively
shorter estrous periods recorded during the dry months, in some 
animals were probably due to the more intense environmental heat 
since mounting was less during very hot afternoons • when the bull or
the heifer might be rather lethargic and less interested. Short estrous 
periods also occurred in other months varying from one individual to 
another probably due to the saml ie rceason. Sometimes estrus temporarily
C J
ceased in the afternoon, and mounting resumed again in the late
evening^night or the folloAwing morning. Heifers showing estrus in 
the paddock in the morning usually stopped mounting when the solar 
heat became more intense especially between 11 and 12.00 hours.
When they had just returned into the pen, their time was spent 
feeding and drinking. Both the bull and the heifer on heat did not 
perform any mounting at that time. The heifer might allow 
mounting by the bull in about one or two hours after feeding or after 
a much longer time had lapsed depending on how hot the day was or how 
long the animals had been delayed in the sun before refcurjifflCj to
the pen
107
Ovulation
The mean intervals of ovulation after estrus ceased, with the 
standard errors, were lU.2 +_ 0.6, lU.7 +. .6 and 15.1 + 0.9 hours 
in UU, 37 and U9 determinations in the Brown, Holstein and Fulani 
heifers respectively. The mean approximate time interval from the 
beginning of estrus to ovulation in these number of cases were 30.9i
29.9 and 30.7 hours in the Brown, Holstein and Fulani heifers respec­
tively. There was no significant difference between the breeds in 
ovulation time (P> 0.05) Tables IX, X and XI)
Generally after a long estrus ovulation occurred within a short 
interval of 6 to 10 hours (table A 2k). The total number of ovulations 
observed was 137. On eight occasions ovulation was not confirmed 
until developing corpora lutea were identified on days U and 5 of the 
estrous cycle. Out of the 129 ovulation that were timed, 105 (81.U/5) 
occurred before or on the day following estrus, 22 (17$) a day after 
and 2 (1.555) on the subsequent day. There was no seasonal difference 
in ovulation time (table XI).
Rhythmicity of estrous cycles
Heifers utilised for this study cycles all the year round, a  
total number of 108, 92 and 105 estrous cycles were considered 
during a year period in the Brown, Holstein aAnd Fulani heifers respectively.
Mean cycle lengths in days, with the standard errors, were 21.0+0.3, 20.1+02 
and 21.U+02 in the order of the breeds (tables XII, XIII, XIV and XV).
108
The differences between the Holsteins and the Fulanis, and
between the Browns and the Holsteins were statistically significant
(P<C0.05). 95, 93.4 and 94.5 per cent of all the cycle lengths fell
wi)thin the 18 - 24-day range in Brown, Holstein and Fulani heifers
respectively. More estrous cycles shorter than 18 - 24-day range
were recorded in the Holstein than in the Brown and the Fulani
heifers, the scores being 6*5 * 0 and 2.2% respectively. EstroWS
cycles longer them 18 - 24-day rancre are regarded as long and the
Fulani scored higher than the Brown and the Holstein* the
frequencies being 7.6, 3.5 and 1.3% respectively. The longest
cycles recorded in the Brown, Holstein and Fulani heifers were
30y 28 and 29 days respectively^
The percentage frequency distribution of estrous cycle lenghs
are presented graphically (fig. 13). From the graph, estrous cycles
in the Browns ranging between 20 - 22 days long showed the highest
frequency. There was a gradual fall from 23-throuah 26-day
frequencies and an outlier of 30-day length. As for the Holsteins*
a peak occurred at 21 day frequency? there was a crradual increase
in frequencies from 17 to 21 days after which a sharp fall occurred
till the .24-day estrous cycle length. The graph for the Fulani
heifers shows that estrous cycle lengths were mostly of the 20-day
to 22-day durations. A smaller number lasted 23 - 25 days. A
few cycle lengths, lasting 27 and 29 on the long side, or 16
to 18 days on the shorter side, tend to broaden the graph* In 
the Fulani, the mean estrous cycle length in days, with the
standard deviation^ in the wet season (21.8 4^2.2) was
109
greater than in the dry season (21.2 .9), but the statistical
significance is quite low (P = 0.05). The values in the Browns,
21.3 + 2.2 and 21.1 + 1.4 days and in the Holsteins, 20.1 + 1.5 
and 20.6 +2.2 days, in the same order of the seasons, showed no 
significant seasonal difference (P̂ > 0.05).
One Brown heifer (Bl) had a peculiarly different pattern amon^
the exotic breeds. The long cycles recorded in the s were
actually all recorded in that particular animal. In that animal
occurrence of 22-day cycles in December - January in the dry 
season was followed by 25 - 26-day cycles in February to March before 
the rains, She showed shorter cycles (21 - 23 days) from April 
till September? durincr October to November she showed long cycles 
of 26 - 30 days after which shorter cycles were shown again in 
December - January. One Holstein heifer showed a Iona cycle of 
28 days in June in the wet season, but this was not repeated.
In the Fulani, roost of the longer estrous cycles (25 - 27 days)
occurred towards the e(nd of the rains and at the beginning of the 
dry season, followed subsequently by shorter cycle lenaths (19 - 23
days) through the dry season. There was a peculiar case in which 
one heifer (F 23) showed many estrus cycles ranging between 25 - 29 
days from time to time through both seasons. Her longest cycle 
(29 days) occurred in the wet season.
Mid-cycle heats were recorded on five occasions in 
a total of four animals: H 148 on day 8 of estrous 
cycle (in December), B 91 on day 14 (April), F 23 on day 20
110
of 27-day cycle (January) and on day 9 (in June)- They were standing 
heat in two cases(B 89 and B 91> A mature C.L. was palpable on one 
ovary in all cases.
Discussion
The Bos taurus heifers observed commenced cycling at a late age
compared to a range of 5 - 15 months reported by £
heat stress as suggested by Vincent (1972). Inadequate nutritional 
level may also be a contributing factor.
The pubertal age recorded in the White Fulani heifers confirms 
the belief that the zebu cattle attain puberty much later than the 
Bos taurus cattle (Reynolds et al 1963; Plasse et al 1968). The 
pubertal age in the zebu cattle studied is, however, lower than what 
obtains under the range system of management reported by Johari and 
Talapatra (1957), Amble et al (1958) and Jochle (1972). The 
nutritional level is lower under the range system and is prone to 
mineral deficiencies compared to the semi-intensive system to which 
the experimental animals were subjected for the purposes of the 
present investigation; and this might have contributed to a relatively 
early onset of puberty in the Fulani heifers.
The high percentage of estrus detected in the heifers (100$)
agrees with the reports by Donaldson (1968) and Wagnon et al 1972. 
Estrus not well expressed and termed subestrus might have been missed
Ill
but for the presence of the bulls and the rectal manipulations of 
heifers suspected or expected to be at estrus. The combination of 
different methods Qf detecting estrus employed in this study was 
responsible for the high percentage scored. Donaldson (1968) was 
able to detect 90% of heat with observations only at 07:00 and 16:00 
hours only; the percentage increased to 100% when observations were 
increased to thrice on cows run with bulls carryinig markers. It
could have been possible to miss estrus in one FuilaSn.i (F20) but 
for the presence of the bulls and the continuous observation since 
she showed low estrous intensity. The combination of methods employed 
in the present study may however be too rigorous to be recommended 
for dairy farms.
Generally estrus was quite recognizable the Fulani cattle.
This was unlike the report by Anderson (1936) that estrus was scarcely 
recognizable in the East African zebu. It seems that the present 
results agree with the observations byRakha et al (1970) with respect 
toestrual- behaviour in African zebu cattle. The intensity of 
estrus ^observed in the zebu in the present study however, is higher 
than what the quoted authors observed. There was, in fact, no dif­
ference in the expression of estrus by two Fulani (F21 and F23) and
the Bos taurus heifers.
112
It does not seem that the environment has altered the estru&l 
behaviour in the Bos taurus heifers. The low estrual expression in 
the afternoon on hot days may just be an avoidance of exercise which 
might increase body heat load, A depressant effect of hot weather on 
estrus has previously been observed by Wolff & Monty Jr. 1974.
Mounting behaviour by the heifer at estrus and standing to 
be mounted by other heifers or by the bull were the most definitive 
estrual signs in the heifers examined. Mounting activity amongygroup 
of heifers was quite indicative of an estrual animal among the group,
as has been previously reported Hafez et al 1969;
Williamson et al 1972)
Most of the other signs of estrus described by previous workers 
were not exhibited consistently and were less reliable than mounting 
behaviour. A vaginal mucus flow can be quite useful in detecting heifers 
at estrus. It could particularly be useful in animals showing only
slight estrual behav: or when two heifers are on heat simultaneously
and are both in the same group of mounting heifers. Since the heifer 
showing estrus also fed freely, like others while in the pen, anorexia 
was not particularly associated with estrus. During estrous period 
the interruption of grazing with mounting while in the paddock, however, 
meant that heifers might consume less grass at that time (fig. 28).
In subestrual cases, a low level of circulating estrogen may be 
responsible for the low expression of estrus. The incidence was low
involving only 17% of the heifers. The frequency (1.5%) of occurrence
113
of subestrus was also low and causal factors can not be identified.
It was however not season dependent.
The economic importance of subestrus lies in the fact that in a 
dairy herd which is not run with a teaser bull, the subestrual animals 
can easily be unnoticed and so escape being bred. This will result in 
unduly prolonged calving intervals.
The distribution of the time of onset of estrus through the 24-hour
day in the present study is similar to some p r e > _  reports. The
greater concentration of onset of estrus between 05.0 a*m. and 12 noon
is however slightly different from the reports on Bos indicus by 
Plasse et al (1970) with concentration at 4 a*m. to 6 a.m., 10 a.m. - 
12 noon and 6 p.ro. to 8 p.m. and the concentrations at sunrise and 
sunset observed by Rakha et al (1970).
Although no definite cause can be ascribed to the greater
concentration of onset of estrus in the morning hours in the present- 
study, the lower ambient temperature at that time of the day may be a 
predisposing factor. The release of the heifers into the field in the 
morning also seemed to trigger off mounting. The lack of significant
effect of the month of year on the time of onset of estrus suggests
that day length and season do not influence the time of onset of estrus.
The concentration of onsets of estrus at a time from very 
early to late morning hours means that the majority of estrus that
occurred in a herd in this environment can be detected when farm
114
workers are on morning duty. The belief that zebu cattle are mostly
on heat and copulate in the night (Anderson 1936; Roberts 1971;
Rollinson 1962) is not borne out by the present result.
Since a proportion of the estrus also commenced in the evening, 
a twice daily check on the animals would be recommend for dairy herds
in this environment. These times should be between 05.00 and fO.OO and
between 17.00 and 20.00 hours in the morning and evening respectively
in order that a very large percentage of animals that come on heat may 
be detected.
The range of the duration of estrus (8 - 31 hours) observed in 
this study agrees with the range (6 - 30 hours) reported by Hammond
1927 in European cattle under temSpePrate climate. Generally, estrous 
periods as long as 20 hours were, however, not very many in the 
present study, constituting 44% of the total timed estrous periods.
The resultsv <h<erre show that the zebu (Fulani) cattle show muchlonger estrus than 4.7 hours reported by Anderson (1944) for east 
African zebu, and 6.7 hours reported in Brahman heifers (Plasse et al 
1970). The present result agrees with the reports in which estrous 
periods ranging between 12 - 24 hours were recorded in Bos indicus 
(Rollinson 1955? Villacorta 1960). Rakha, et al (1970) also reported 
that zebu and some other African breeds showed long estrus in Central 
Africa with a mean of about 16 hours, thus agreeing with the present 
observations. The observed long estrus in the Fulani in the present
115
study is particularly remarkable in that it negates the previous 
assumption that zebu cattle in this environment might be showing very 
short estrous periods r
Previous climatic laboratory reports have shown that the estruus 
period is shortened by exposing temperate types of cattle to hot 
environment (Branton et al 1957; Gtengwar et al 1965)A. Normal
duration of estrus was not regained after heifers had reestablished
cycling in a hot environment that had caused ry anestrus (Bond
& MacDowell 1972)• The present result shows t<hadt the shortened 
duration of estrus in cattle in the field due to environmental heat 
is not a permanent defect as the report by the latter authors tends 
to suggest. In the field, the effect on estrual expression of the 
environmental heat and particularly solar radiation may not even
last much longer than the actual period of exposure,
The present result also does not agree with an earlier observation
that estrus was h1Xl7ly dcetectable in temperate breeds of cattle in hot
weather (Poston*r et al 1962) . It shows some similarity to that of 
Wolff and Monty Jr. (1974) in which there was no significant difference 
between the duration of estrus in cool and hot seasons in non- 
lactating Bos taurus cows. pccurrence of estrus as short as 8 to
12 hours or as long as 20 hours or more, depending on the animal and 
the ambient condition of the day, and in both dry and wet seasons, 
suggests that the influence of the day is more important than that of
the season in determining estrous period length in the field.
116
Direct solar radiation may be an important cause of the depres­
sion of estrual behaviour in some afternoons. The fact that the animals 
had to spend most of the afternoons in the shade of the pen has aided 
the prolonged estrous periods. It is most likely that exposure of a 
heifer at estrus to direct solar radiation continuously throughout 
the day may considerably shorten the estrous period. Keeping cows in 
the shade in a hot natural environment has been shown to improve 
fertility (.WtefSPW ip Stpkb, 1969) . By cutting off direct solar radiation 
which may impose severe heat load on the animals and which may
therefore cause a depression of estrus, shvadeV structures allow the 
prolonged expression of estrus which may increase the chances of 
the heifers being detected and br estrus artificially or by the
bull.
Generally only an estimate of the time of ovulation was possible 
in view of the time incte-rrvals of ovarian examination which might have
been responsible for the ovulation interval being longer than what was 
obtained (10.5 hours) in a much earlier report (Trimberger 1948).
Since the first ovarian examination just a few hours after the end of 
long estrous periods revealed ovulation, it is possible that ovulation 
occurred before the end of some long estrous periods.
The present result, by showing no seasonal difference in 
ovulation, supports the reports by some previous workers that hot 
season did not adversely affect ovulation (Hall et al 1959; Plasse et 
al 1970; Wolff and Monty 1974). Spring and summer conditions have
117
been associated with reduced occurrence of abnormal ovulations in 
Friesians, Afrikaner crosses, and Afrikaners in South Africa (Van 
Rensburg and De Vos 1962)• The relatively high ambient temperatures 
prevalent throughout the year in the sub-equatorial environment where 
the present study was conducted have been propitious for normal 
ovulations rather than being inhibitory.
Spermatozoa cam survive for 15 to 24 hours i „ J 2 r  reproductive 
tract of the cow after insemination (Krillov 1937; Andrew 1937). In 
view of the time of ovulfction obtained in the present study insemination 
of heifers towards the end of estrus would ensure that ovulation 
coincides with the time when spermatozoa are present in the reproductive 
tract of the female, and hence a high conception rate may be
achieved. &
Hot conditions have been associated with reduced release of L.H. 
in cattle (Madan and Johnson 1972; Miller and Alliston 1974). This 
condition may be expected to affect ovulation. Since a large per­
centage of ovulation occurred before or on the day following estrus in 
the heifers examined, it is probable that pituitary L.H. release may 
not be adversely affected by the climate of the region where the 
present investigation was conducted.
The lack of breed differences in ovulation suggests that the 
ovulation process in Bcs taurus cattle is not differently influenced 
by tropical climate from that in zebu cattle (Fulani). Van Rensburg 
and De Vos (1962) similarly found no breed differences in ovulation 
between the Afrikaners, Afrikaner crosses and Friesians in South Africa
1 18
The result shows that variations may occur in the length of 
successive estrous cycles within and between breeds of cattle. The 
number of estrous cycles shorter than 18 days (2.8$) obtained in the 
heifers fall within the range (2.2 - 6.8$) in reports reviewed by 
Rollinson 1962; but cycles longer than days (U.0$) were less than
13$ given in that same report.
in the Bos taurus heifers observed are similar to those previously 
reported (Trimberger and Hansel 1955; Hansel and Trimberger 1952;
Asdel 19^9). Results obtained
to some reports on zebu cattle (Villacorta 1960; Rakha et al 1970;
Plasse et al 1970); the mean interval of estrus was* however, a 
little longer in those reports than in the present result.
Previous studies in the laboratory by Bond et al (i960),
McDowell (1972), show that heat
stress causes only temporary anestrus in Bos taurus cattle. This 
is prognostic for the continuous cycling of that type of cattle 
acclimatised to a tropical environment. The heifers observed could 
adjust as the seasons changed especially in an environment with 
relatively high ambient temperatures throughout the year.
The present result showing no seasonality in the sexual activity 
of zebu cattle does not corroborate previous reports that zebu show 
greater preference for the dry season for breeding (Wilson 19^6). 
There is also no indication that the animals are influenced by
119
photoperiod in their sexual activity, unlike the postulate by Anderson 
(1948). It has been suggested that high ambient temperature is 
stimulatory to fertility in zebu or other African types of cattle 
(Thompson 1973? Jochle 1972? SteinbacH & Balogun 1971; Wilson 1946), < 
Probably, this meteorological factor has contributed to the 
regular recurrence of estrus in the zebu heifers throughout the year,
thus agreeing with the report of Anderson (1948) th<atp high temperature
is stimulatory to sexual rhythms. < P
It is possible that the semi-intensive management to which 
the animals had been subjected for the present experiment, which is 
different from the range system ^ „ h i c  h zebu cattle are naturally 
maintained, had also contributed to the maintenance of regular estrous 
cycles during the dry season. There are indications that low 
mitritional levels can depress sexual rhythm and conception rate in 
Bos indicus (Rakha, et al 1970; Carneiro 1950). The seasonal peaks 
in breeding and conception rate in zebu herds under range management
reported by the various authors quoted above, may be an ecological 
adjustment to increased breeding late in the dry season or early 
rainy season so that parturition will occur in the dry season or 
close to the rainy season but not so much in the rainy season.
This avoids exposing young calves to high parastie challenge. In spite 
of such adjustments under range management zebu cattle are shown by 
the present study not to show a preference for any particular period of
120
the year for increased sexual activity. The same is also true for
the temperature breeds of cattle.
However, because of the problem of feeding during the dry
season, it is advisable to regulate the breeding of cattle in the
environment of the present study. Calving can be made to occur during 
dry
the/season when the calves would depend solely on milk and concentrate 
feeding. By the time the rains start and the grasses grow, the
digestive system of the calves would with
roughage. Calves can then utilise the pasture together with the 
concentrate supplement and maintain rapid growth through the rainy 
season. Thus, a steady rapid growth can be achieved in calves during 
the first year of life.
The cause of mid-cycle heat observed in the present study is 
not known. Wagnon et al (1972) found that the difference in the 
occurrence of mid-cycle heats or "short estrous cycles" between the 
stressed and unstressed cattle was not statistically significant.
The stresses applied were managemental, including transportation, 
branding with hot iron and introduction to new environment.
From previous reports, it has been shown that a wave of follicular 
growth occurs in cattle ovaries from days 3 to 4 of the estrous cycle 
(Coles 1930; Hansel 1959? Rajakoski 1960). The largest of these fo~ 
ll/cles persists till mid-cycle before undergoing atresia. Large 
follicles (1 4 - 1 5  millimeters in diameter) have been found from the 
8th to 13th day of estrous cycle in the ovaries of cows. Probably, the
121
estrogenic secretion from such follicles at their mature size at 
mid-cycle is sometimes high enough to cause behavioural estrus, and, 
even, standing heat observed in heifers in the present study. Wagnon 
et al (1972) found that two consecutive short estrous cycles were 
equal to one normal cycle and this agrees with the present observations. 
Although the frequency of occurrence of mid-cycle heat is very low, 
the implications in a breeding programme can be important. Cattle
bred at mid-cyclc estrus can not conceive since estrus is non­
ovulatory and this can result in labour loss and waste of material 
in an artificial insemination programme.
122
X I I . Plasma cortisol concentrations in heifers during estrous cycles and 
different quarters of the year
Results
The composite curves of plasma cortisol concentration during 
estrous cycles (Figs 14, 15, 16, 17) were broken before proestrus 
because of the differences in the number of estrous cycle days 
within breeds. For convenience of numbering, the day of estrus is 
referred to as day uO".
Plasma cortisol concentration in the heifers in the majority
Marked occasional elevations
in individuals are masked in the composite graphs. The graphs show 
that plasma cortisol levels fluctuated throughout the estrous cycle. 
Elevated levels or more pronounced fluctuation occurred around the 
day of estrus in individual heifers. In a few cases, however, the 
level on the day of estrus was not different from those of the other 
days of the cycle. Elevations might occur as early as three days 
before estrus. Plasma cortisol levels on the day after estrus, about 
ovulation time, was often lower than that on the day of estrus, though 
it was also high in a few cases. Lower levels and fluctuations'in 
plasma cortisol occurred during diestrus especially about the middle of 
the estrous cycle. Such lower levels were however interrupted by
occasional elevations. The fluctuations in the plasma cortisol
123
concentration -were less marked and levels were generally lower 
during estrous cycles in November through the middle of January 
than in other periods of the year.
Analysis of variance (Table A 27) shows that the value on the 
day of estrus (mean of 8.9 ng/ml) for all the heifers through the 
year is significantly different (P ' 0.01) from the mean for the
cycles (5.8 ncr/ml) . The mid-cycle value (5.5 ng/ml) was not 
significantly different from the mean (P>0.05).
The mean plasma cortisol levels in individual animals during 
the different periods of the year, and the mean for each breed are 
in tables A 25, A 2G and XVI. Aynalysis of variance (tables A 28aand b) shows that the effects gf season on plasma cortisol level is 
significant (P\0.01). Significantly higher levels (P< 0.01) of 
plasma cortisol were obtained in July/August (6.5 ng/ml) and 
March/April (6.1 ng/ml) periods. Analysis of variance also shows 
that there was no significant (P '• 0.05) breed effect on plasma 
cortisol values. "The grand means of plasma cortisol for the Brown 
Holstein and Fulani heifers in the year were 5.9, 5.8 and 5.7 ng/ml 
respectively. Breed x season interaction was also not significant
(P> 0.05).
The pattern of change in the plasma cortisol levels through 
the seasons was slightly different among the breeds. The 
relative rise in the mean levels during the March - April period 
in the Brown and Holstein did not occur in the Fulani in which 
the rise occurred only in the July - August period (fig. 18).
124
Discussion
Generally the values of * basal* plasma cortisol concentration
agree with the values obtained in cattle by competitive protein binding
method in previous studies: for example, a mean of 2 - 5 ng/ml
with elevations up to 25 ng/ml at estrus in heifers, a range o%f 1 - 5.1
ng/ml basal levels in heifers, and a mean of 8.04 ng/ml in steers 
reported by Gimenez et al (1974), SatterleS ot al V I 977) , and Abilay, 
Mitra and Johnson (1975) respectively. A previous study using
radioimmunoassay also obtained a similar rang^e  of Vbs a- sal plasma 
cortisol levels (3.6 - 10 ng/ml) in heifers (Dobson & Kancher 1977)
In the present study, the levelIs o:f plasma cortisol in the heifers
are, however, quite low compared to those in a previous study in non- 
iactating cows using similar method of blood collection (Venkataseshu 
and Estergreen 1970). The cows in that study were not accustomed
to handling and venipuncture. Previous studies have shown that 
low plasma cortisol levels can be obtained in sheep that are trained 
or adapted to the procedure of handling and venipuncture (Linder et 
al 1964; Basset and Hinks 1969, McNarthy and Thurley 1973). The 
adaptation is believed to be controlled by the central nervous system 
In the present study the value of training animals was reflected in 
the low levels of plasma cortisol. The present study shows that such 
an endocrine study requiring repeated venipuncture should involve a 
period of training for the animals, and procedures should be uniformly 
continued throughout the duration of the study. The handler must
125
as much as possible not be changed and must use the same technique 
every time. The restraint period should be as short as possible as 
has also been indicated in other studies (Heitzman et al 1970; 
Gimenez et al 1974; Lee et al 1976).
The present results show that "basal' plasma cortisol levels 
in the heifers were slightly but significantly higher during the wet 
months than during the dry hot months. In a few previous field
studies, it has similarly been observed that plasma cortisol levels
in cattle were depressed by seasonal heat (Stott and Wiersma 1971;
Lee det al 1976). Excretion of 17-ketogenic steroids had similarly 
been found to be reduced in sheep iLnr ^su,mmer (Robinson and Morris 1960)
Seasonal differences in environmental temperature were less
marked in the geographical area of the present study than in those of 
the previous studies quoted. The relatively low ambient temperature 
in July and August is however distinct when compared to other months
of the year. It is possible that homeostatic mechanisms in tropical 
animals are sensitive to the relative seasonal changes in ambient 
conditions including environmental temperature just as animals in 
temperate and cold -regions can be sensitive to the alternating cold 
and hot seasons. The lower adrenocortical function in the heifers 
during the dry hot months in the present study may, to some extent, 
be due to the depressant effect of heat.
In a previous study, it was found that adrenocortical function in 
sheep was increased under cold wet conditions (Panaretto and Vickoy
126
1970). The wet and cooler conditions might also have been responsible 
for the slight increase in adrenocortical function during the rainy 
season in the present result. Future studies may explain the 
mechanism of such a phenomenon. However, the slight lowering of 
adrenocortical function in the dry hot months in the present study may 
be a form of thermoregulatory adjustment to reduce metabolic heat 
load due to circulating cortisol, since this hormone has been shown
to be thermogenic (Yousef & Johnson 1967). This phenomenon has been
described as protective (Yousef & Johnson 1967,. ilay, Mitra and
Johnson 1975).
Since haematocrit values were n ecreased in the hot dry season
(table A  ID) the reduced levels of plasma cortisol during the dry 
season can not be attributed to ̂ aemodilution. Since Christison & 
Johnson (1972) have shown that in cattle, the release of cortisol is 
depressed by heat and that the metabolic clearance is constant, the
seasonal changes in plasma cortisol in heifers in the present study 
may not be attributable to changes in metabolic clearance but to 
variation in the rate of functioning of the adrenal cortex. As part 
of the present investigation, high adrenocortical responses to 
exogenous ACTH both in magnitude and duration were found in the 
heifers, suggesting that the magnitude of response by adrenal cortex 
may be proportional to the level of circulating ACTH. Seasonal 
alteration in the level of circulating ACTH rather than changes in
127
adrenocortical responsiveness, or actual depression of adrenal 
cortex by heat per se, may therefore be responsible for the seasonal 
difference in adrenocortical function in the heifers. Further 
experimentation demonstrating seasonal levels of ACTH in heifers is 
suggested.
The fluctuations in the level of plasma cortisol from day to day 
in the heifers agree with previous reports (Sprague et al 1971?
Arije et al 1971? Gimenez et al 1974? Abilay et al 1975). The more 
exaggerated responses occurring on the day of estrus or around 
estrus have also been similarly observed in some studies (Arije et 
al 1971? Gimenez et al 1974? Shaw, Dutta and Nichols 1960).
The fact that a sharp increase in plasma cortisol was not observed
on every morning of the days of estrus . may suggest that 'increase<dc 
cortisol release did not occur continuously through the day of 
estrus. Blood samples miaht have been taken when the plasma cortisol 
levels were still low, preceeding or after the rise. Perhaps more 
blood samples taken at other times of the day of estrus would have 
indicated the increase in plasma cortisol level as was observed in 
a previous study (Gimenez et al 1974). The elevation on the day 
of estrus was however found to occur both in the morning and afternoon 
samples in studies in a climatic laboratory (Miller and Alliston 1972)» 
The last three quoted reports and the present study do not agree with 
the result of Abilay et al (1975) in the psychrometric chamber with
128
respect to the level of plasma cortisol on the day of estrus which 
was found to be lower than other .days of the cycle in the latter 
report.
The elevated plasma cortisol level around estrus might in part 
be due to increased activity and excitement in the heifers about 
that time. If this is true, elevation of plasma cortisol Concentration 
around estrus would hardly be avoidable in heifers in the field. Some 
other factors influencing the hypothalamic-pituitary-adrenocortical 
function may also be involved, and thus make the elevation more 
pronounced since similar reports had been obtained in restricted
cattle in the reports quoted above.
If the finding by Sandberg anid Slaiunwhite (1959) that estrogen
increases the amount of cortisol bound in the blood of man is true 
for cattle, a reduced feedback effect of cortisol at the pituitary 
level would be expected to occur during the estroaenic phase of the 
estrous cycle since less free cortisol would be in circulation.
This may result in a general increase in plasma cortisol concentration 
around estrus. Increased estrogen just before or at estrus might 
also have stimulated increased ACTH since such effect of estrogen had 
been reported in rmts (Gemzell, 1952).
It is not known if elevated plasma cortisol before and at estrus
has any effect on corpus luteum similar to the suppressing effect on 
corpus luteal development observed when ACTH was administered from days 
2 through 8 of the estrous cycle (Brunner et al 1969). The role of
129
plasma cortisol at estrus may be luteolytic as suggested for plasma 
cortisol in cows near term (Adams and Wagner 1970).
Since ovulation and expression of estrus occurred normally, 
increased circulating cortisol around estrus probably did not 
disturb the release of pituitary and gonadal hormones in the heifers. 
This is contrary to the observation in rats and cows injected with 
exogenous glucocorticoid in other studies (Baldwin and Sawyer 1974?
Liptrap 1970).
A relatively low level of plasma cortisol during many days in 
the luteal phase of the estrous cycle may suggest a lowered 
adrenocortical secretion during the luteal phase. This is not similar
to the results obtained by Abilay , Johnsson and Madan (1975). It is
however similar to the results obtained by Gimenez et al(1974) 
except that the present result shows relatively more elevations 
during the luteal phase. In the latter previous report, plasma 
cortisol levels were generally low during the luteal phase perhaps
” 9
because the animals were restricted. Low adrenocortical secretion 
also occurs in cows during pregnancy, a luteal period (Heitzman et 
al 1970; Adams and Wagner 1970; Arije et al 1971). Low adreno­
cortical function during an active luteal stage may be desirable 
because of the suppressive effect of cortisol on corpus luteal function
(Brunner et al 1969? Adams & Wagner 1970).
130
The generally lower levels of plasma cortisol over the estrous 
cycles during the drier hot months than during the wet cooler 
months may be an expression in the field of a similar phenomenon 
observed in heifers kept under constant high or circadian high 
and low temperatures of psychrometric chambers in two separate 
studies by Abilay, Johnson & Madan (1975) and Miller and Allison 
(1974) respectively. The role of such lowered adrenocortical functions
on fertility has not been defined. Monty Jr. and Wolff (1974) 
suggested that it may not be the cause of reduced fertility in 
cows in the hot Arizona summer since injections of dexamethascne
at the beginning of the breeding season did not improve fertility.
Higher circulating plasma cortisol concentrations during the 
wet and cooler season may imply an increased catabolic effect of 
cortisol on tissue protein and increased mobilisation of amino 
acids for gluconeogenesis (Ray 1968; Burkey 1973). Tissue protein
catabolism dur iat time of the year may, therefore, effect
a lowering of jht gain. However, the terms ’low' and 'high*
used in this discussion for the values of plasma cortisol obtained 
during the different quarters are only relative. Really high values 
that could cause marked metabolic problems did not occur. In fact 
the greatest weight gains in the heifers during the year were 
obtained in the wet season and tended to coincide with the rainfall
peaks.
131
Low plasma cortisol level is also believed to occur in 
ruminants during drought as a result of low nutritional level and 
thus indicating low metabolic rate (Macfarlane 1968)• The lower 
plasma cortisol concentration in the heifers during the dry hot 
months may therefore be suggestive of a lower metabolic rate during 
that period. A reduced performance associated with the lower 
metabolic rate was probably shown in the reduced body weight or 
weight gains in the heifers during November through January in the
present study.
The onset of the rains in March through the rainy season was
accompanied by growth of lush grass. This also resulted in 
increased grazing and growth rates, which could have been associated 
with increased metabolic rate and a general increase in adreno­
cortical function.
The mechanism by which cortisol increases the body resistance 
to disease is not fully known (Burke, 1973). It is however possible 
that increased adrenocortical function might increase the resistance
of the animal.ss to the stress of parasitic infestation and high 
numbers of biting insects prevalent during the wet season.
These results show that temperate-evolved cattle, once 
acclimatized to a tropical environment, may not necessarily have to 
maintain adrenocortical functions conspicuously different from local 
cattle, particularly when not under any stress of production.
However / more investigations are still needed to explain the
132
mechanism involved in the role of adrenocortical hormones in 
homeostasis. More definite explanation for the seasonal variations 
in adrenocortical function in heifers under tropical condition can 
only emanate from such further work.
133
IV* Diurnal and circadian changes in physiological 
responses and plasma cortisol concentration
Result
Respiratory rates and rectal temperatures 
During the period when the physiological responses were
recorded, air temperature varied from low morning values to peak
values in the afternoon at about 16.00 hours dines in air
temperature occurred from about 17.00 through 07.00 hours -when the 
lowest values were recorded. The lowest relative humidities were 
also recorded at about 16.00 hour. Sunshine occurred before 09.00
or 10.00 hours and was very high $before mid-day till about 16.00 
hours.
Responses in heifers in the sun
Mean readings of rectal temperatures and respiratory rates are
in tables XVII and A 29. The results of analysis of variance of the 
readings are in tables A 30 and A 31. See also fig. 19. Mean
rectal temperatures ranged from low morning values of 100.0, 101.0 
and 100.8°F to high afternoon values of 103.2, 106, 102.8°F, in the 
Brown, Holstein and Fulani respectively. Analysis of variance 
(table A 31) shows that time and breed effects on the rectal 
temperatures were each significant (P<0.01). The difference between 
readings at 07.00 hours and other times of the day was significant
134
(P< 0.01) but there was no significant difference between the 
readings at 11.00 hour and subsequent times till 18.00 hours. Thus, 
rectal temperature rose sharply to a maximum reading at 11.00 hours 
or at a later time. The significant (P<f0.01) breed effect was 
due to the abnormally high reading in two Holstein heifers (104.4°F 
(40.7°C) in H 145, and 106°F (41.1°C) in H 154) compared to the 
highest readings in: the * Brown <103.2°F (39.5°SC) and the Fu-lani <162..
. C39.3°) There was no significant (P^ 0.05) difference between
the Brown and Fulani in the rectal temperature change, but the 
Holstein was significantly different (P<"0.01) from these other two 
breeds in this respect. However, analysis of variance shows that the 
time of the day contributed more^(60%) to the total(72.5%) 
variations that occurred than did breed effect 10%).
Mean respiratory rates ranged from low morning values of 
26.8, 38.6 and 16.7 to high afternoon values of 50.1, 92.2 and 
28.8 breaths per minute in the Brown, Holstein and Fulani heifers
respectively. Analysis of variance (table A 30) shows that time
(PC 0.01) and breed (P^O.Ol) effects on respiratory rate were 
significant. Time and breed interaction was also significant (P<'0.01)
By 11.00 hours, the Holsteins had started panting and this continued 
right into the afternoon when breathing rates as high as 110 per minute 
were recorded. Breathing rates in the Brown and Fulani were also 
elevated but not as much as In- Hdlsteins; and afternooh values ranged
135
from 58 to 68, and from 26 to 44 in the Brown and Fuiani respectively. 
By 18.00 hours a little decline in respiratory rates occurred.
Correlation analysis (table A 32) shows that rectal temperatures 
(P<0.01) and respiratory (P^O.Ol) rates were significantly cor­
related with the environmental temperature, the correlation co­
efficients being 0‘.7 and 0.5 respectively. Rectal temperatures 
were also positively correlated with the respiratory rates in the 
different breeds, the correlation coefficient being 0.8, 0.9 and 0.7 
for Holstein, Brown and Fuiani respectively, and these were significant 
(P<^0.01). Using the Iberia Heat Tolerance test (IHT) on the mean
rectal temperature at about 16.00 hour< r(ambient temperature of about
90 o F) the heat tolerance coefficiveOnty for the Brown, Holstein and 
Fuiani heifers were 85.2, 70.5 and 87.6, The lowest individual 
scores were 66 and 50 in Holsteins H 145 and H 154 respectively. 
Physiological responses; j# heifers under shade
The mean rectal temperatures and respiratory rates, with the 
standard errorg/ in heifers kept in the shade are in table XVIII.
The result is also graphically represented in fig. 20. Analysis 
of variance shows that the time effect on rectal temperature was 
significant (P<̂  0.01) , but breed effect was not (P> 0.05) . Time of 
the day effect contributed -more (39.9%) than breed effect (3.6%) 
to the total variation (43.3%). The afternoon rectal temperatures 
were not abnormally elevated.
136
Analysis of variance shows that time (P<0»05) and breed (P^O.Ol) 
effects on respiratory rate were significant. There was, however, a 
significant (P - 0.01) breed x time interaction. Breed contributed more
effectively (53fi>)t han time of the day (31̂ ) to the total variations that 
occurred (83.3$)•
Correlation analysis shows that respiratory rate in the shade was 
positively correlated with the rectal temperature, the correlation 
coefficient being 0.38, 0.47, 0.48 in Brown, Holstein and Fulani heifers 
respectively and these were also significant (,P v 0.05» P<0.01, P < 0.01
respectively).
The results of analysis of variance comparing the readings of 
respiratory rate and rectal temperature in the shaded with unshaded 
heifers are shown in Table35 A. 34,^4 35 respectively. They show 
that the type of treatment (shade or sun) has significnat (p x 0*01) 
effect on the rectal temperature and respiratory rate. The readings 
in the heifers when not shaded were significantly (P^O.Ol) higher than
the reading when shaded. As regards respiratory rate, significant 
(P^O.Ol) two-way interactions were breed x time of the day, breed x type 
of treatment and time x type of treatment.
With regard to rectal temperature, time of the day was more 
effective (37$) than type of treatment (10̂ >) or breed (T7°) in 
contributing to the total variations On the other hard*
breed effect contributed most (525°), compared with time of the day 
(27#) or type of treatment (5$), to the total variations that
occurred in the breathing rates.
137
Circadian rectal temperature and respiratory rate in the shade
The mean values of the rectal temperature and respiratory rate 
are in table XIX. From the analysis of variance, time and breed 
had separate significant effects on the rectal temperature (Table A 33) 
Time factor was # however* more effective (54.7%) than breed effect (6%) 
in the contributions to the total variation (61.5%). Time and breed
effects on respiratory rate were also separately significant (P<f 0.01). 
Time x breed interraction was again significant (P^O.Ol).
Rectal temperatures and respiratory rates between 11.00 and 23.00
hours were significantly (P<^0.01) higher than between 07.00 and 11.00 
hours. The physiological responses were low and changed in a
similar pattern as the ambient tjeQmpyerature but with some time lag
(fig. 21) &
Correlation analysisA dalso shows that respiratory rate and 
rectal temperatures were positively correlated, r = 0.6, 0.9 and 
0.6 in the Brownf Holstein and Fulani heifers respectively, and these 
were all significant (P^O.Ol) .
Plasma cortisol
1. Results from experiment 1 (tables XX and A 36) are 
presented graphically (Fig 22) and show little variation in the levels 
of plasma cortisol at the three times of blood collection. Analysis 
of variance of the values (table A 38) shows that breed and time had 
no significant effects (P>0.05) on the values obtained. Breed x
138
time interraction was not significant (P^0.05). Plasma cortisol 
level ranged between 2.2 and 8.8 ng/ml during the 3 sampling 
times.
Rectal temperature did not vary consistently with plasma 
cortisol level, correlation coefficients being -3, 0.5 and 0.5 in 
the Fulani, Holstein and Brown respectively (table A 39) . The 
significance of the correlations also varied from low order (P = 0.05)
in the Holstein and Brown to nil (P>0.05) in lani.
2. The three animals involved in I enxperiment 2 showed reluctance 
when they were being separated from the group and throughout the 
morning they showed some desire to join the other heifers. The 
values of plasma cortisol obtained are shown in table KK i Morning 
high values of plasma cortisol 17.3, 14.1 and 9.7 ng/ml in the Brown, 
Holstein and Fulani respectively, were progressively decreased to 
lower values of 9.2, 5.1, and 3.5 ng/ml in the same order of breeds
by 19.00 hours.
3. The diurnal plasma cortisol concentrations (tables 
A 37) are shown in graphical form (fig. 23) . There were individual 
variations in the level of plasma cortisol throughout the periods 
of blood sampling and there was no consistent pattern. Generally the 
values tended to be similar to morning values. In the Brown, the 
values tended to be generally higher in the morning than in the 
evening;while the values in the Holstein and Fulani as shown by the 
curves from the mean levels were fairly stable with a small relatively
139
higher level at 11.30 hours in the Holstein. Analysis of variance 
(Table A 40) shows that time and breed had separate significant 
effects (P< 0.01). Breed x time interaction was not significant 
(P>0.05). One heifer (H 154) showed very high plasma cortisol 
level in the morning (19 ng/ml)(table A 37) but much lower level 
at subsequent times. Values from this animal were not used when
the breeds were compared and in constructing the graph of the mean 
values.
4. The circadian levels of plasma cortisol (tablesJr*///and 
A 41) are presented graphically (fig. 23). Analysis of variance
shows that breed and time effects were not significant (P) 0.05). 
Breed x time interaction was not significant (P>0.05) (table A 42). 
Fluctuations occurred in the plasma cortisol levels in individuals 
through the circadian period. Both the pattern and levels of plasma 
cortisol through the circadian period were not similar among the 
individual heifers. Values obtained in the coccygeal venous blood
were less than 10 ng/ml of plasma and similar to those of jugular 
venous blood (Table A 41).
Plasma cortisol levels in heifers kept outdoors in experiment 
3 were similar to values in experiment 4 in which animals were 
under shade throughout the day. Generally, values obtained in 
experiment 1 heifers outdoors in the afternoon were lower than the 
values obtained in experiments 3 and 4 in and out of shade respectively 
at about the same time of the day.
140
As typical of the weather conditions in this environment, daily 
dry bulb temperatures rose from a minimum value at 07.00 hours to a 
peak at 16.00 hours during the period of the investigation. A 
precipitous fall in air temperature occurred between 18.00 and 19.00 
hours followed by a more gradual decrease through 07.00 hours.
The levels in plasma cortisol did not show a similar trend to
the ambient temperature. Relatively elevated or low l1evels might 
occur in different individuals when the ambient temperature was 
quite high.
Discussion
The present study shows that circadian changes occur in the 
physiological responses of the heifers of Bos taurus and Bos indicus 
under natural hot climatic conditions; and this agrees with the 
previous observations in Bos taurus under subtropical hot climate 
(Berman 1967, 1968; Berman and Morag 1970). The similarity of the 
trend in diurnal and circadian physiological responses to that of 
ambient temperature indicates that the latter influences the former.
The high responses in the sun show the effectiveness of 
solar radiation as a strong heat stress factor, thus supporting 
similar prior observations (William et al. 1960). The lack of breed 
differences in the heifers continuously under shade is due to the
fact that heat stress had been minimised by the shade structure.
The response of individual heifers also shows that when 
hyperthermia occurs in the hot weather, it lasts for only a short 
period during the day time and not continuously. This is not in
agreement with a laboratory study in which responses were proportional 
to the applied heat stress (Worstell and Brody 1953).
The higher responses in the Holstein heifers particularly in 
the sun indicate a lower heat tolerance than in 'the Brown and Fulani, 
as confirmed by the Iberia heat tolerance test. The low heat 
tolerance in the sun also shows that the solar radiation must have 
imposed heat load more rapidly than body could dissipate heat.
A poorer cutaneous evaporative heat loss mechanism as well as a 
lower protection by the coat against heat load in the Holsteins than 
in the Browns and Fulanis is indicated.
The modifying effect of shade structures on the physiological 
responses observed in the present investigation agrees with the 
findings of Rainey, et al (19 6 7) and Romance-Pounce et al (1977) in 
dairy cows. The result of a supplementary observation comparingihe 
non-lactating cows with the heifers (table A U3), showing lower 
responses in the shade than in the sun, also indicates that both 
groups of animals would benefit from shade structures in the field.
The non-significant effect of the time of the day on plasma 
cortisol values obtained in experiment 1 indicates a more or less
142
uniform concentration through the day time, resembling the results 
from a similar investigation by Shaw et. al. (1960). In experiment 
3, the higher mean values by 11.00 hours and lower mean values by
15.o0 or 18.00 hours which were in many heifers similar to the 
morning (07.30 hours) values were responsible for the significant 
effect of time of the day in the analysis of variance.
The fact that relatively elevated levels of plasma cortisol 
occurred in some heifers at the time when the levels were relatively 
low in others signifies the lack of uniformity in the pattern of 
adrenocortical secretions among the heifers through the diurnal or 
circadian period. The significant effect of time shown by the 
analysis of variance on some values did not therefore indicate the 
existence of a definite rhythm in plasma cortisol. The factors that 
can be examined for their contribution to the result obtained include 
the experimental procedure, ambient conditions and hypothalamic- 
pituitary-adrenocortical rhythm. The heifer^ utilized for the study had 
been accustomed to handling including blood collection for 5 to 12
months before these investigations were carried out. The additional 
preconditioning before the blood samples were collected further helped 
in training the animals.
The intervals of sampling were over one hour so as to reduce 
the effect of handling since the heifers were not catheterised.
As much as possible the procedure of blood collection was quite fast 
so that prolonged handling which could have resulted in struggling
143
was avoided. The advantage of speedy blood collection in obtaining 
physiological plasma cortisol levels had been noticed by other 
earlier workers (Heitzman et al, 1970? Gimenez et al. 1974? Lee et 
al 1976). Collection of large volumes of blood, which was avoided, 
could have caused a prolongation of the time of handling and restrain­
ing the animal which could show up in elevated plasma cortisol levels
as in sane previous renorts (Venkataseshu and Estergrieen 1970? 
Patterson 1957).
With regard to the intervals of sampling, early studies on 
plasma corticosteroid periodicity in man had employed intervals of 
4 to 6 hours which are longer than those used in the present study,
3 ?
and were able to describe a smooth rise and fall in corticosteroid 
levels (Migeon et al. 1956). The use of shorter intervals of sampling
(20 - 30 minutes) only enabled more detailed description of the
periodicity, with respect to the episodic secretions of plasma 
corticosteroid (Krieger et al. 1971; Heilman et al. 1970). The 
interval of sampling employed in the present study might not have 
precluded the observation of a plasma cortisol rhythm if it existed 
in the heifers. The low levels of plasma cortisol also indicate minimal 
influence of the method of blood collection and this could be a measure 
of adaptation. The use of the tail vein did not significantly alter 
the level or pattern of plasma cortisol concentration obtained 
despite the relatively lower excitement during tail blood sampling.
This further justifies the view that the heifers were adapted.
144
The striking aspect of the results is the generally low levels 
of plasma cortisol concentration in the different investigations. 
Acute exposure to heat has been shown in laboratory studies to 
cause sharp elevations in plasma cortisol in cattle (Stott and 
Robinson 1970; Christison and Johnson 1972; Alvarez and Johnson 1973; 
Abilayf Mitra and Johnson 1975). The heat of the tropical afternoon
did not evoke such marked elevations in adrenocor functions in
the heifers. Since the circadian plasma cortisol levels did not show 
a similar pattern to that of the ambient temperature, the latter 
might be influencing the former to a very limited extent.
It is possible that some of the low peaks at about 11 or 
12 hours were due to the effect of ambient temperature and/or solar 
radiation. High ambient temperature has been shown in a previous
study to be capable of causing increased cortisol release by setting
up impulses at the skin thermoreceptors which then stimulate the 
hypothalamic CRF release (Chowers, et al 1966). The time point 
when the environmental heat or solar radiation was effective enough 
to excite the thermoreceptors might vary among the heifers depending 
on how quickly the skin temperature increased.
Under thermal exposure, the skin temperature of zebu cattle
increases more slowly than that of Bos taurus (Ojo 1973; Allen 1962). 
The thermoreceptor of the Bos taurus might be more quickly excited 
\ander the present experimental conditions and this might be responsible
145
for some breed differences in the diurnal plasma cortisol among 
the heifers. The lack of uniformity in the values of plasma cortisol 
among the heifers in the afternoons does not, however, suggest that 
the adrenocortical function was responding to the ambient heat, ,
From the results obtained, there was also no evidence to show that 
the adrenocortical response in the shaded and unshaded heifers differed.
The species differences in the binding capa i of cortisol
binding glubulin (CBG) has been reported to b« iponsible for species
differences in plasma cortisol concentration (Linder 1964). CBG
concentration was not determined in the heifers used for the present
investigation and the contributio&n o-vf-r  4t-1his factor to the slightspecies difference in diurnal variration of plasma cortisol could 
not be assessed.
The lack of uniformity among the heifers in the circadian levels 
of plasma cortisol suggests that routine management practice might 
not have imposed any permanent influence on their adrenocortical
function unlike the suggestion in a previous report on dairy cattle 
(MacMam and Eberhart 1972) . In species showing uniform variations 
in circadian plasma cortisol, the rhythm has been associated with 
circadian CRF and/or ACTH release. in the present observations, 
repeatability of cortisol periodicity was not demonstrable as to 
level and pattern in the different animals used unlike what was 
demonstrated in man (Krieger et al 1971). This therefore does not
146
suggest the existence of a rhythm in ACTH release in the heifers, 
although it was said to be probably responsible for adrenocortical 
rhythm in cattle in another previous report (Wagner and Oxenrfeider 
1972).
The present observation in a way, therefore, agrees with some 
other previous works in which definite diurnal adrenocortical
rhythms could not be demonstrated in cattle (Paape eu a1 1973;
Paape et al. 1974; Hudson et al. 1975; Shaw etsQiHp' 1960) . Hudson et 
al. (1975) explained that the rhythm is lacking in cattle probably 
because cattle, like other ' * ‘ wake for considerable
time in order to ruminate 1967)
Some mechanism must be operating to keep plasma cortisol levels 
in cattle low in a hot environment (Bergman and Johnson 1963; Rhynes 
Ewing 1973; Christison and Johnson 1972). The purpose of such a 
mechanism may be to avoid increased metabolic heat production due to 
the thermogenic action of cortisol (Yousef & Johnson 1967). This
mechanism may be preventing marked diurnal variations and a definite 
rhythm in plasma cortisol levels, such as have been described in other 
species. The results of experiment 2 further support this suggestion, 
and show that the mechanism operating to keep plasma cortisol levels 
low or to correct any elevations due to management or environmental 
stress may be of greater priority than that to maintain a diurnal or
circadian rhythm in cattle, especially in a hot environment.
147
The reluctance shown by the animals in experiment 2 while they 
were being separated from their usual group was responsible for the 
elevated plasma cortisol values particularly in the morning. 
Separation of an animal from the usual group in the herd can be 
stressful. In normal dairy practice, this type of managemental 
stress is hardly avoidable since animals may be separated from their 
usual group for various reasons including breeding at estrus.
The inconsistent trend m  the association een rectal
temperature and plasma cortisol in experiment it (table A 36) is due 
to the more stable levels of the latter at the times of blood sampling 
than the values of the former. The more highly positive correlation
between the physiological responses and the ambient temperature (table 
A 32) r and the lack of a definite pattern of plasma cortisol through 
the day further indicate an absence of definite association between
the physiological responses particularly the rectal temperature and
plasma cortisol. In a laboratory study, similar trends in the 
elevations of plasma cortisol and rectal temperatures were found in 
cattle under thermal stress (Abilay, Mitra and Johnson 1975). It 
might be expected therefore that in the field, the diurnal plasma 
cortisol levels should show a trend similar to tthat of the rectal 
temperature of cattle. This was not found to be true in the present 
study, as the pattern of change in the levels of plasma cortisol did 
not resemble that of the rectal temperature in view of the more 
persistent rise in the latter in the afternoon till sometimes late
in the evening.
In another study carried out in the climatic chamber, it has
however, been found that elevated plasma cortisol levels lasted for 
only a short period while elevated rectal temperatures persisted 
during thermal stress (Alvarez and Johnson 1973). This is prognostic 
for responses under natural hot climates where adrenocortical function 
in acclimatized cattle may, therefore, be less sensitive to ambient 
heat than is rectal temperature and may not show a similar trend
as rectal temperature, diurnally. This suggestion is borne out by
the present results.
The level and pattern of plasma cortisol during the circadian
period in individual animals may have some relationship to 
adaptability. Further stu^ie8 are still needed to examine this 
relationship in both adapted cattle and those newly introduced to 
hot natural climate.
149
V. Effect of exogenous corticotrophin on adrenocortical 
functions and estrous cycle
Result
The mean weight of heifers treated with ACTE:! was 317.5 
kg. Tiie minimum and maximum environmental temperatures on the day
ACTH was injected were 72°F (22.2°C) and 89'JF (31.• 7°C) , a:nd the
.relative humidities were 87% and 54% respectively plasma
cortisol concentrations in the heifers are in a A 44 and are also
presented graphically (figs. 25 and 26).
Mean pre-injection value of plasma cortisol concentration 
varied between 3.2 and 5.2 ng/ml. A sharp rise in the level was 
obtained at 30 minutes after ACTH injection. Peak values ranging 
between 41 and 62.4 ng/ml occurred between 30 - 140 minutes post­
injection of ACTH and were 10 to 15 times higher than the initial 
levels. The percentage change in plasma cortisol concentration from 
the initial values ranged between 872 and 1304 among the heifers.
There was a tendency for a plateau to form before the decline 
in plasma cortisol concentrations occurred. The declines started 
between 140 - 300 minutes post-injection of ACTH and were either 
gradual or rapid. The initial pre-injection levels were closely 
approached but not reached in 5 of the .six heifers. High levels 
occurred till after 6 hours post-injection. Plasma concentration
150
of cortisol 24 hours after ACTH injection were low. The response 
levels, that is, post-injection plasma cortisol concentration higher 
than initial levels, had a mean of 33,0 (jd.6.0 SD) and a range of
5 . 5 -  61 ng/ml in the heifers.
In the control experiment, the elevation in plasma cortisol 
was low compared to that after ACTH treatment, and ranged between
1.6- 3. times the pre-injection level between 30 - 120 minutes 
post-injection of saline. The levels of plasma cortisol on the day
following the ACTH injection were also low.
The analysis of variance of the results of the two treatments 
is in table A 45. It shows that the time interval, type of treatment .cand t' 
breed effects on the level of plasma cortisol were separately 
significant (P<0.01), being 103.79, 40.54 and 971.17 at
degrees of freedom 8 , 2 , and 1 respectively. There were, however,
significant (PI 0.01) two-way interactions between time interval
and breed, time interval and type of treatment, and breed and type
of treatments There was a significant (Pi 0.01) 3-way interaction 
between time interval, breed, and type of treatment. The total 
variations that occurred (70%) were due to the effect of the time 
interval (30%) and the type of treatment (36%), while the contribution 
from breed effect was very little (2%).
Analysis of variance on values of plasma cortisol obtained from 
ACTH treatment alone (table A. 46) shows again the significant (P^O.Ol)
151
breed, time interval and two-way interaction between the time 
interval and breed effects. With saline treatment alone (table A 47), 
breed effect was not significant (P J 0.5) as well as br€£-ci x time 
interval interaction (P> 0.05) ;;but time interval effect was 
significant (P{ 0.01) .
Estrous cycles at the time of ACTH treatment lasted 1 8 - 2 3
days in the heifers. Estrous cycle rhythmicity was therefore not
altered by the treatment.
•
Discussion
Because of the method of blood collection, it was not possible 
to collect blood samples at very short intervals of 10 minutes or 
less as was done in some previous studies which employed venous 
catheterisation (Paape et al 1973; Paape et al 1974; Shayanfar 
et al 1975 ?'. Satterlee et al 1977). The method employed here 
did not, however, prevent the observation of distinct adrenocortical
v v
response to ACTH, and this has similarly been observed in some 
earlier studies which employed venipuncture for blood collection 
(Venkataseshu and Estergreen 1970; Shaw and Nichols 1963;
Dobson and Kanchev, 1977).
Pre-injection levels of plasma cortisol obtained in the present 
study were similar to values normally obtained in the same heifers 
during the year, and to values in some earlier reports by Swanson et al 
0.972) and other groups of workers quoted above.
152
The significant effect of the type of treatment on the level 
of plasma cortisol obtained was due to the stimulatory effect of 
ACTH on adrenal cortex as has been reported in earlier studies quoted. 
The elevation found in control experiment might have been due to 
the stimulation of the adrenal cortex by ACTH released from the 
pituitary in response to non-specific stimulus including the method 
of blood collection (Venkataseshu and Estergreen 1970; Shaw and 
Nichols 1963)%r The influence"of the piethod of blood collection 
might have been responsible for the slightly higher levels of 
plasma cortisol in the control experiment (range 3.05 - 10.22 ng/ml) 
in the present investigation, compared to values obtained in an 
earlier report (0.7 - 7.7 ng/ml) under hot and thermoneutral conditions 
(Satterlee et al 1977). Compared to previous studies quoted above 
in which jugular venipuncture was employed, the values obtained 
k € r e in the control experiment were not high; and
this can be attributed to adaptation in the heifers which had 
experienced protracted training and sampling through the year.
The significant effect of the time interval after the injection 
of ACTH on plasma cortisol concentration is mainly due to increasing 
secretion of cortisol into circulation as time progressed until a 
peak production was attained, thus agreeing with reports quoted above.
The significant two-way and 3-way interactions are due to the 
lack of uniformity in the pattern of change in the levels of plasma 
cortisol with time among the individual animals. Although the study
153
was not to compare the breeds, a breed factor was introduced to 
facilitate the use of analysis of variance to test the values. 
Incidentally, the values in the Brown heifers were higher than in 
the Holsteins and the Fulanis. Kajela (1973), quoted by Shayanfar 
(1975), did not find any breed difference between the Holstein and 
Jerseys in the adrenocortical response to ACTH. What is striking
in the present result is the marked individual difOfeSre'nces between 
the heifers in the responsiveness of the adrenal cortex to ACTH.
The weight differences between the heifers were small and could 
not have been responsible for the differences in the adrenocortical 
response among the individual heifers. The significance of this 
finding, however, is that although the basal levels of adrenocortical 
secretion, hence the plasma cortisol level, may be similar, the 
potential of the adrena^ cortex for maximal secretion of corticoids 
varies among the heifers. This may also suggest individual differences 
in adrenal weight or the amount of cortical tissue in the adrenal gland, 
Rollinson (1962) stated that there had been indications of species 
variation in adrenal weight* with Brahman and Brahman crosses having 
heavier pituitary glands and lighter adrenal gland than British breeds.
A definite work on this was, however, not quoted.
%
The adrenocortical response to ACTH in the present study are 
similar to those reported earlier in heifers (Satterlee et al 1977; 
Dobson & Kanchev 1977) . This result is also comparable to that
154
obtained in dairy cows in another study (Shayanfar et al 1975). It 
therefore, suggests that the metabolic state may not alter the 
potentials of the adrenal cortex of cattle, inspite of the reported 
elevated normal basal glucocorticoid . secretions in lactating cows 
(Vanjonak and Johnson 1975).
Under natural weather, adrenal responsiveness to ACTH was 
found to be less in dairy cows injected on days with environmental 
temperatures above 21.1°C than those injected below this temperature 
it was suggested that adrenocortical responsiveness to ACTH could 
be depressed by environmental heat (Shayanfar et al 1975). In
cattle raised in a hot environment', ^thhee  riesponsiveness of their 
adrenal cortices to ACTH might therefore^ be expected to be low. The 
present result shows that the responsiveness of adrenal cortices 
of acclimatised heifers is not depressed by the tropical condition. 
This, therefore, substantiates the result of a study conducted in
the climatic laboratorryy showing that adrenocortical responsiveness
to ACTH in heifers acclimatised to hot environment (35_ oC 80% RH) 
was s i m i l a r t h o s e  in a cold(5°C 30% RH) and thermoneutral (18°C 
5®*̂ RH) conditions (Satterlee et al 1977) .
The depressant effect of chronic environmental heat on adreno­
cortical function in cattle has been well documented as shown in 
various reports cited in previous chapters. The present result 
shows that the low adrenocortical function in cattle exposed for
155
prolonged periods to heat can be'altered by ACTH. The 
normally low plasma glucocorticoid concentration in cattle exposed 
chronically to thermal stress may, therefore, be due in part to a 
depressed pituitary ACTH release rather than a depressed s e c r e t o r y  
ability of the adrenal cortex alone.
The result also shows that the normal functioning of the 
adrenal cortices of the heifers under the subequatorial and the
experimental conditions described was much lo1 an the potentials
of the glands. The heifers, therefore, had high adrenal reserves.
The lack of an effect of ACTH administration on the .estrous 
cycle length suggests that induced elevation of endogenous glucocorticoid
at-'and after mid-cycle period did not induce a luteolytic process- 
This corroborates previous report which showed that exogenous 
glucocorticoid did not alter estrous cycle when administered at mid-
cycle period (Gimenez et al 1974); it is, however, contrary to the 
report that adrenal supression with betamethasone caused prolongation 
of estrous cycles (Kanchev et al 1976). The fact that ACTH adminis­
tration, hence increased circulating glucocorticoid, can suppress 
the development of corpus luteum in cycling heifers,as demonstrated 
by Brunner et al (1969), or that glucocorticoids can trigger luteolysis 
during late pregnancy may not necessarily mean that high levels of 
circulating endogenous cortisol at the middle of estrous cycle, and 
thereafter^ can induce luteolysis.
156
SUMMARY AND CONCLUSION
It has been found that the basal level of plasma cortisol in the 
German Brown, Holstein-Friesian and White Fulani heifers under the sub­
equatorial climate ranged between 1 - 1 0  ng/ml and showed no breed 
differences in the grand mean (5.8 ng/ml) through the year. This 
suggests that acclimatised temperate-evolved cattle do not necessarily 
have to maintain adrenocof.tical functions differently from local Ccittle
in a tropical environment.
Seasonal difference in the level of plasma cortisol in the heifers
was slight but significant, being lower in the dry hot season than in
the wet relatively cooler season. This may result from a generally
lowered metabolic rate during the former period. Frequently, higher 
adrenocortical activity occurred a few days before or on the day of 
estrus when plasma cortisol concentration might be as high as 22 ng/ml.
Tills phenomenon was also more marked in the wet season than in the dry 
season^ the fluctuations in the levels were less marked in the latter period. 
Rectal temperatures were normal with a mean of 101.3°F (38.5°C) 
and 102.2°F (39.0°C) in the morning and afternoon respectively for 
all heifers together through the year. Although seasonal variation was 
little, it was significant, with lowest afternoon rectal temperatures 
occurring in the wet relatively cool months of July and August. There 0005 
some indication of slight seasonal shift in the basal rectal
157
temperature in some heifers showing higher values in the wet season 
than in the dry season. Differences between the morning and afternoon 
readings of rectal temperatures were lowest in the wet cool period.
Breed differences were mainly due to the slightly lower body temperatures 
in the Fulani, and the greater occasional recurrence of hyperthermia in 
the Holstein heifers thus agreeing with previous reports that rectal 
temperatures in Bos indicus are less elevated than in Bos taurus under 
high-temperature evironments (Findlay 1954; Worstell and Brody 1953).
Respiratory rate varied diurnally and with greater amplitudes
between mean morning values of 14 - 44 and mean afternoon values of
17 - 75 breaths per minute in the shade. The low and high readings were 
recorded in the Fulani and Holstein heifers respectively. Breed dif~ 
ferences were therefore highly significant. Seasonal variations 
were well marked as in subtropical observations in other earlier reports.
Although the mean afternoon rectal temperatures were generally not 
abnormal, the higher values in the relatively hotter and dry season was 
associated with high respiratory rates, sugaestina accelerated stimulation
of adaptive functions during that period of the year. These effects 
were more exaggerated in the Holsteins and suggest intolerance of the 
afternoon heat and of elevations in the body temperature. Generally, 
therefore, the Holsteins apparently attempted to maintain normal body 
temperatures by increased respiratory activity.
The results show that the lowest afternoon and diurnal variations 
in rectal temperatures and respiratory rates in the heifers occurred
158
during the period of the year when basal plasma cortisol levels were
highest. If the increased adrenal function suggests higher metabolic 
rate, the low physiological response indicate that such increased 
metabolic rate was associated with greater comfort for the animal 
during that period of the year, that is, the wet relatively cooler l . 
season. It is not known if the seasonal variation in the quantity of 
available pasture, hence nutrition, influenced the suggested alterations 
in metabolic rate. The slight seasonal changes in both the basal
(morning) and afternoon rectal temperatures, however, suggest that 
some shift in the set-point for temperature control may occur between
the different periods of the year.
In spite of the relatively low basal secretions of cortisol, 
adrenocortical reserve was high since adrenal response to ACTH (200
I.U.) was high in magnitude and duration. Adaptation to a hot humid 
tropical climate did not alter the potentials of the adrenal cortex.
Low normal basal secretions may therefore be part of a general 
adaptative thermoregulatory control in a tropical environment to avoid 
increased metabolic heat production which might result from the thermogenic 
action of cortisol. The adrenocortical responsiveness to exogenous 
ACTH may also suggest that the seasonal variations in adrenocortical 
secretions is due to seasonality in the levels of the circulating 
ACTH. This will require verification.
The changes in rectal temperatures and respiratory rates over 
the circadian period paralleled the changes in ambient temperature with 
high positive significant correlations and with peaks occurring in the
159
afternoons. These responses did not resemble that of the plasma 
cortisol concentrations which showed no consistent patterns. This 
suggests that adrenocortical function was less responsive to diurnal 
or circadian ambient conditions than were the physiological responses, 
in heifers in the shade and in the sun.
On one occasion in the sun,, however, there was a tendency for
higher adrenocortical secretions at about raid-day ( A1 1 . 0n0n  _-_ 13.00 hours)
than in the evening (19.00 hours). Some species differences also 
occurred as the White Fulani showed lower responses than the Brown and
Holstein heifers.
The physiological responses wer:e more e-xaggerated in all heifers
when exposed to the sun. Direct solar radiation was generally not 
tolerable to the Bos taurus breeds but the degree of tolerance varied 
between and within the breeds. The Holstein heifers were more hyper­
thermic in the sun; they panted, sought shade and therefore spent less 
time grazing than the other breeds when the heat was intense. The lower 
heat tolerance of the Holsteins, therefore, became more clearly evident 
on exposure to the sun. The Brown and the Fulani heifers did not pant 
in the sun. The Fulani heifers were generally able to tolerate the sun. 
The high breathing rate, and the avoidance of the sun plus the hyper­
thermia exhibited by th$ Holsteins in the sun, may suggest a lower 
efficiency of the increased population of sweat glands previously
reported in animals of this breed when acclimatized to tropical conditions
160
Estrus recurred in the heifers throughout the year. The majority 
of estrous periods commenced during daylight with the greatest concentration 
in the morning. It should be possible to detect almost all heifers on 
heat by close observation at between 07.00 and 10.00, and 18.00 and
2 0 .0 0  hours, although with observations in the morning alone a large 
percentage of estrus should be detected. Mean estrous cycle lengths 
(with standard errors) were 21.0 + 0.3, 20.1 + 0.2 and 21.4 + 0.2 days in
the Brown, Holstein and Fulani heifers respective! showed no
significant seasonal variations. The mean duratic strus, with
the standard errors, were 16.2 0.7, 15.6 0.8 and 14.6 0 .8  hours
in the Brown, Holstein and Fulani heife respectively. Seasonal
differences were not significant and the duration in the two species 
compared well, although the breed differences were slightly significant, 
Estrual behaviour was depressed by intense afternoon heat and direct 
solar radiation particularly in the Bos taurus. Estrus was well 
expressed in the Bos taurus and the Bos indicuS heifers although the 
intensity was occasionally low in a few individuals among the latter.
Ovulations occurred well within a day after estrus with no 
significant breed and seasonal differences. Silent ovulations were not 
observed, but subestrous conditions occurred. Subestrous m ight pass 
undetected under systems utilising less vigorous estrous detection methods. 
Results of observations for estrous cycles, therefore, generally suggest 
that heifers of both Bos taurus and Bos indicus cattle can breed at 
all periods of the year under Ibadan conditions. However, because of
161
the seasonal nature of the available pasture9 it is suggested that 
heifers and cows should be made to calve early in the dry season, when 
the calves would depend only on milk and concentrate feeding. By the 
time the rainy season starts and the grasses grow, the calves should 
be mature enough to digest roughage and thus utilise the pasture, A
steady fast growth rate can thus be achieved through the first year
of life.
Rectal temperatures did not show any cyclic pattern during the 
estrous cycles. Contrary to some previous reports on the effect of
exogenous glucocorticoid in pigs and rats, vnoVrmal elevation of
endogenous plasma cortisol levels eith mid-cycle perioc
or around estrus in the heifers prxa^^Ly did not disturb LH release
since ovulations and the expression of estrus were generally normal.
Estrous cycle rhythmicity was also not altered by exogenous ACTH 
(200 I.U.) administered between days 10 to 15 of estrous cycle.
Elevated endogenous glucocorticoids, therefore, did not elicit luteolytic
effects in the cycling heifers%in spite of the reported depressing effect 
of ACTH administration on CL development (Brunner et al 1969).
The fact that the heifers were protected from solar radiation for
most of the day throughout the year might have greatly contributed
to the generally low seasonal differences in some of the parameters.
The ability of the heifers to maintain homeostasis with relatively
uniform effort throughout the year can be said to be reflected in the
low seasonal shifts in rectal temperatures and plasma cortisol levels
as well as the lack of seasonal differences in the estrous cycles. The
162
respiratory rates, however, shovedthat adaptive functions were brought 
to play to different magnitudes in the different breeds.
Because of their consistent avoidance of direct solar radiation 
and the ease with which hyperthermia developed in the Holsteins in the 
sun, Bos taurus cattle should be provided with shade structures under 
the conditions of Southtern Nigeria. Grazing in the night throughout 
the early morning hours should also be mandatorily adopted.
The ease with which the Browns dominate ove: Holsteins suggest
8 ™
that a mixed herd of these two breeds should notW be encouraged. Access 
of the Holsteins to shade in the field and to feed in the pen is 
precluded in the mixed herd; and this can have adverse effects on 
production.
' The German Brown cattle should be recommended over the Holsteins 
for the hot humid Southern Nigeria environment since the former are 
more adapted as reflected in their physiological responses. The Southern
Nigeria conditions caAn deffinitely support large cattle establishments 
stocked with the German Brown cattle if the problem of seasonal availability 
of pasture can be overcome. There is need to utilize irrigation to make 
pastures grow ail year round. Sufficiently large quantities of silage 
should be prepared against the dry season. Management should ensure 
that heifers show steady weight gains through the years until mature 
weight is attained.
These results show that the Fulani cattle are more adapted to the 
hot/humid sub-equatorial climate than the Bos taurus cattle, Their
*
163
qualities with respect to estrous cycles were also elucidated. 
Artificial breeding is as applicable for the Fulani as for temperate- 
evolved cattle.
Better management practices are needed for the Fulani cattle. 
Maintained under identical intensive or semi-intensive management, 
the temperate-evolved cattle in the tropical environment may prove to 
provide no advantage over the Fulani cat'' ’ ' " " ‘ * ity.
The high cost of importing and managing
for further investigations on the relative economics of production when 
this type of cattle and the Bos indicus are maintained under identical
management in the tropical environ £ southern Nigeria. Thus, ’
the need to import temperate-evolv . tie may be re-evaluated.
Further areas of study in this particular environment that can
be suggested include:
(1) Investigations of adrenal reserves through the seasons in Bos
indicus and Bos taurus cattle.
(2) Investigation of possible progesterone/cortisol interaction (Adrenal 
secretion of progesterone is believed to contribute to plasma levels 
of that hormone; this has been suggested in previous works as a  ̂
factor in the aetiology of infertility in cattle in a hot environment).
(3) A study of gonadal functions with respect to hormone secretion in
Bos indicus and Bos taurus cattle.
164
(4) A study of the influence of seasons on fertility in Bos taurus 
and Bos indicus cattle under the same management with particular 
regard to effects on conception,
(5) Investigations of adrenocortical functions and physiological
Table 1
M ean  R e sp ira to ry  ra tes  in  h e ife rs  d u rin g  d iffe ren t
q u a rte rs  o f the y e a r
f- - “ ~ *'—--t--- — - ->■—* -\ *. ~ ii Brown Holstein Fulani
; faa 1 5 6
A M P M A M PM | A M PM
Dec(4th) - 20.8 31.0 | rt.a 55^Tr 19.3 24.6
Jan (14th) +0. 5* +0.5* ! i®* 6 + 1.6 : +0.4 JO. 5
i
_ _ n _ i_ _* _  ^ 252 252
i‘  210 * 3 2^10 252 252..
March (9th) - : 30.6
+0. 6 30.0
65.1 21.7 27.4
April (19th) i +~ 0.9 +1.2 +0.4 +0.5!
n 252 25$* • 210 210 252 252
July (5th) - 16.0 19.5 | 22.5 27.4 15 18 ,
August (17th) ! +0.6 | +0. 6 +1.2 | + 0.4 + 0.4 j
n I -X
i
46 4 264 ! 220 i
| ""ri 
220*n~  1 rii 
264 264 _j
October (23rd)- <tt27.7 50.7 i 30.8 69.6 \ 16.8 29.2 i
Dec. (2nd) | -  0* 7 +0.7 !1 JO. 6 + 1.6 +0.5 J0.7 1
. ....« ^  ‘ ‘ 246 246 ! 205 205 »i 246 246 !
♦a number of animalsr standard error
n number of observations
Table II
Mean percent change in respiratory rate at 15.00 
frcnr values at 0 7 .0 0 hour S
period ! Brown Holstein Fulani
DcC- 71.8% 104.4% < % rM . s %
tfflN SD) (_+17 .2 SD) (V #.0 SD)
' ' ' s V ......
WftRtH 46.2 27.4
ftfZiL. (±26.5 SD) (_+ 4.8 SD)
!
Twi-V 23.1 | 21.9<P n  .3
fluCruST fjl'lO.S SD (+_ 5.3 SD) (+ 7.4 SD)
... .
Oc7 — 84.5 134.6 75.3
f40V (+22.6 SD) (+35.2 SD) (+^5.2 SD)
J— — --- C l
S D = Standard deviation.
r—>
-£» CD
1 6  7
Table III
Mean morning (07. OOh) and afternoon (15, OOh) rec tal tem peratures along with the
Brown 6b Hoistein ^  ^ Fulani 6b
07 .OOh 15 .OOh 07 .OOh 15.OOh 07 .OOh 15,OOh
Dec. 4 - 101.2+0. 4°F 102.3+0. 6°F 101.2+0. 6°F 102. 4+0. 5°F 101.2+0. 3°F 102.1+0. 6°F 
Jan. 14 (38. 5°C ) (39. 0°C) (38. 4°C ) (39. 4°C ) (38. l^C ) (38. 9°C )
n 252 j  252 210 ^  210 252 252
March 9 - 101.3+0. 6®F 102.2+0. 6°f 101.3+0. 4°p 102.4+0. 5°F 101.2+0. 5°F 102, 1+0. 3°F 
A p ril 19 (38. 5°C ) | (39. 1°C) (38. 5°C ) (39. 1°C) (3 8 .4°C ) (38 .9 °C )
n 252 ! 252 210 210 252 252
July 5 - 101. 3 +0. 5 °F  102.1+0. 3°f 101.3+0. 4°F 102.2+0. 6°F I ! 101.2+0. 2°F  102. +0. 4oF 
August 17 38.5 (3 9 .0°C) 38. 50C (39. 0°C) (38. 4°C ) (38, 9°C )
!
n 264 264 220 220 264 264
1 — .:.- r '! 1 y v  1 1
October 23 - 101.2+0. 6°F 102. 3+0. 5°F 101.3+0. 5°F 102.5+0. 7°F 101. 2+0. 2°F 102. 2+0.
“  "
Dec, 2 (38. 5 °C )5 x (39. 1°C) (38. 5°C ) (39. 2°C ) (38. 4 °C ) (39°C )
n 246 246 205 205 246 246
1 i U
b = number of animals 
n = number of observations.
Table IV
Mean age of commencement*'of estrous cycles in Brown, 
Holstein and Fulani heifers.
Breed Brown Holstein Fulani
.. . • <
Mean 17.6 23.7
Standard deviation _+1.6 + 1.8 + 1.9
Range (months) 16-20 20-25
Number of animals 6
6 ^  
.......
“W’t , , v  
* = Pubertal age
»
CO
169
Table V
Percentage distribution of time of onset of estrus
in heifers
—
Fulani Brown Holstein 
0 - 1 $ • n = T p . n - l i f
Time of the day (hours)
20:00-01:00 4.3 4.0
6 C
01-07:00* 3aS:' 38.6 32.4
07-12:00 41.3 44.2 48.6
. .......  > c
| £-20:00 20.7 12.8 14.9
--------------- < £ -----:
*Estrus commencing between 01:00 and 07:00 hours were 
more concentrated between 05:00 and 07:00 hours. 
Generally most estrus commenced during the day time 
especially in the morning hours, fl- number OF observations
Table VI
Duration of egtrus jn heifers through one calendar
year
Wet Season Dry Season All Year Round
Breed Mean S E n* Moan S E n* Mean S E n*
.......... . h '__  .... __
Brown n * 6 17.5 M.O 36 15.6 *0.9 31 16.2 _+0.7 67
Holstein "  f
n = 5 16.0 +1*1 31 15.2 *0.9 30 15.8 _+0.7 61
Fulani n = 6 15.4 +1.2 37 13. T̂* 1°-7 30 14.6 _+0.8 67
S E = standard error
n - - number of observations
n = number of animals.
171
Table VII
Breed comparisons of the duration of estrus in heifers
Brown versus Brown versus 1 Holstein versus 
Holstein .Fulani Fulani
DF 126 .. 132 .. 126
t 0.7 2.0
P >0.05 £  0.05 >0.05
.NS NS
t = student t~value; p = level of significance; 
DF = degree of freedom;_..s = significant,
NS = not-significant.< Table VIII
Comparison of the.  duration of estrus in heifers during the
and dry seasons
Brown Holstein Fulani
DF BS sq 65
_t..__  -1.3 1.2 1.3
P > o, os >0.05 70.05
NS NS NS
DF * Degree of freedom; t = student t - value, 
P 3 level of significance; NS * not significant.
172
Table IX
Ovulation interval (in hours)
n = number of observations
Table X
Compar? son of ovulation interval after the end of estrus in heifers
. . . . . . . . . -  ^ • Brown Versus |r B—rown- -V-e- r- -s-u-s-  - - - - 1Breed Holstein Versus Holstein Fulani Fulani
Degree of 
freedom 80 91 85
* . . ...  . _ _ _ _ 1 _ _ . . . . . . . . . . . . . . . . . . . . .
t 0 . 6 0 . 8 0.3
P >0.05 >0.05 >0.05
t ~ student t -value; p = level of significance
Table XI
Ovulation interval after the end of estrus in Brown,
Holstein and Fulani heifers 3 observations in the
wet and dry seasons compared
Wet Season Dry Season 
(March - October) (November - Feb]ruary)
S V
xffl) SE n x SE n
x » meanj SE = standard error 
n = number of observations during each season
DF = degree of freedom 
t = student t - value
p = level of significance.
174
Table XII
The character of the frequency of estrous cycle lengths in ,
heifers
Fulani
EstfbuScycle lengt(hisrjdbys)
Mean 
S ♦ E o
Longest (days)
Shortest (days)
Between 18-24 days (%) 
Above 18-24 days (%) 
Below 18 days (%)
Number of observations
>
Number of animals
.75
Table XIII
Estrous cycle lengths in heifers through the wet and dry seasons
Dry season Wet season . Total observations
Mean length Mean length Mean length 
(days) SD n (days) SD (days) SD n
r /n\<A2  
n*
n V
Broyrn 6 21.3 2 . 2 51 21.1 1.4 57 2 1 . 0 3.0 108
Holstein 5 2 0 . 1 1.5 4 1 2 0 . 6 2 . 2 51 I 2 0 . 1 +1 . 6 92
Fulani 6 2 1 . 1 1.9 48 < T 57 21.4 +2 . 1 105
1.. _________________
SD = standard deviation
n = number of observations
176
Table XIV
Comparison of estrous cycle lengths in the 
wet and dry seasons
!
1[ Brown Holstein ... Fulani 
!
* ’ —
Degrees of
freedom 106 90
t 0.5 1 . 1 ' s? 1 . 6
y.005 >0.05 s/P = 0.05
NS NS*
1 *
t = student t - value 
p - significance level 
NS = not significant
NS*= not significant (but slightly longer values in 
the wet season).
177
Table XV
Comparison of the estrous cycle lengths in the Brown (B) 
Holstein (H) and Fulani (F) heifers
p = level of significance
S = significant
NS = not significant.
T a b ic  X y?
M ean  jjlajyn.a c o r t is b l concentration * in h e ife rs  d u rin g
t&ffereat quarter* o f  the y e a r
' ri .r 1Season < Brown
t Holstein j Fulani
i 6** 5** j 6**
Dec. 4 - 5.1 4.6 5.7
Jan. 14 i■ +0. 5 a +0. 4a +0. 6 a
i
n i\ 87 ! 87 96
March 9 6 . 1 6.3 5.7
Apr! 1 19 +0.5 +0.4 ±0.4
- ----------- j---- ---.9.6...... 1 110
<1-----
9-6--- t?------ --
July 5 - 6.5 6.6 6. 3
August 17 +0.4 +0.4 ±0.4
1
a 98 , 96___ i 98__.
i
October 23 - ; 5.6 | 5.3 ! 5,
Dec. 2 +0.4 ; ±0.4 , +0.4
105 1 0 2 109
* - plasma cortisol concentration (ng/ml) 
a " standard error 
** * Number of heifers 
a  ~number of observations.
n ci
Table XVII
Mean rectal temperature a and respiratory rates in heifers 
kept outdoors In the sun throughout the -day time
Time of Brown Holstein Fulani
the day(h) (°TF*) n = 6 n  - 5 n m 6
Tre RR Tre RR Tre RR
0.700 75 100.9 28 ' 101 36.8 100.8 18. 00
r J[ i.0.5b +2. 3 ±0.5b +0. 5b +0. 5 b +3. 2 b[’ " --
11.00 ! J 102. 0 47.6
+0.3 j6. 2 1'
96 101.7 27.9
+10.213 1+1.3 i +0# 3 +6.3
. . .. _ _J ii  — .. .
15.00 8 8 102.0 58.4 103.9 94 102.5 36.4
+0.2 +0.5 +0.9 +5.7 +0.2 +6.1
1*i. 00 1 8 2 102. 1 57.2 1(B.2 85. 6 101.7 31.2i + 0. 1 +5.0 HO.6 + 3.3 +0. 5 1
n = number of animals 
b = standard error 
Ta - Ambient temperature (°F) 
RR = respiratory rate 
Tre = rectal temperature (°F)
Observations were made on three occasions
ISO
T ab le  X V I I I
Diurnal rectal temperatures and respiratory rates' of heifers
in the shade
T ime of Mean
the day(h) Ta and RH Brown Holstein Fulani 
__ ' . n = 5 n = 5 n = 5
1 TA RR T RR T RRt n A re i re
07 no 72* 5 92 100. 8 52.4 100. 8 34.8 101.6 16.7V  I  0 U K J
_ +0.4b +3. 8b + 0.4 +4.1 [- . +.0. ...4 . • +2.61
11.00 78 77 101.2 35.4 101 70.3 101.2 21.8
+0.4 14. 2 ±0.2 +4.? +0.4 ±4.2
13. 00 85 68 101.2 37.5 101.8 74.4 101.2
+0.2 +0. 3 +4.5 +0.1 2+86.+0.9 .7
9
16.00 88 57 101.* 38.0 102. 0 74.4 101.5 28. 0
+0. 1 +1.5 +0.3 ±4.8 +0.2 +6.7
19.00 1i 78 65 101.3 35.8 101.7 68.6 101.1 21.4+0.2 +0.9 +0.4 +1.8 +0.3 +3.4
23. 00 77 88 101.0 28. 0 101.2 47.6 101 16. 0
+ 2. 6 +2.6 +0.4 +7.9 +0.3 +1.7
n = number of animals
T re = Rectal temperature (°F)
RR = Respiratory rate (Breaths/minute) 
Td = Ambient temperature (°F)
RH = Relative humidity (%) 
b = standard deviation 
Observation were made on two occasions.
181
Table XIX
Circadian rectal temperatures and respiratory rates of 
heifers in the shade
• • •
TIME OF THE BROWN* HOLS']PE IN* FULANI*
DAY O ')
w E E Ire
i PR
___-r1rt ._.......h.r... .
07 - 100.9 30.0 100.9 38 100.9 ’ 17.608 + . 4 f +2 . / +2 .6/ +3.2/ ±3.1/' ±2 .6/
 - 1 0 1 . 34 1 0 1 . 2  71.6 101.2 25 1 0 1 1 + . 1 +4 + . 1 +3.8 + .1 +3.0
- -____
13.-14 101.3 40 1 0 1 . 8  101.2 33.2 
+2 +6.4 + . 1 il0.i + .1 +5.2
16 - 17.OC 101.5 42. 101.3 33.6 
±  -2 6 . 1 T # +6 . 6 + . 1  + 2 .6
 - 1 0 1 . 1  37.6 6 0 .8 101.2 34.8 20 2 1 + .2 +3.8 c +8.4 + .2 +4.1 
j____ _
 - 1 0 1 . 1 27.;tK, 1 0 1 . 2  35.6 1 0 1 . 0  16.8 0 1 02 + .2 j S y + .2 +3.3 + .3 +2.3
04 - 05 1 0 2 . 0  26.3 1 0 1 . 6 33.6 100.9 16.4 + . 1 +2.7 + .2 +3.8 +1.0 +1.7
___ z__s__
* number of animals = 5 
/ standard deviation,
RR = respiratory rates 
Irg = rectal temperature ( *? )
182
Table XX
*]Vturnal plasma cortisol concentration in heifers (ng/ml)
(Experiment 1)
—
TIME OF ------------ i •
THE DAY BROWN* [ HOLSTEIN* F ULAN if' AMBIENT
(HOUR) CONDITION!
. \ ___
4.3 4.2 4.9
07.30 S 3° i
t o - s f +0 .6/ +0.7/-/' 92%RH
5.2 6.4 89°F
1 2 . 0 0 i! +.4 +1.4 +1.9 70%RH
!| .. . ..  /
|}\
4.3 4.4 90°F
17.00
| ' ■ \ d* . 2 +0.3 6 8%RH
1
=. number of animaAls = 4
/ = standard error
Blood samples werde Collected from heifers kept in the sun 
throughout the day as described in the text.
183
Table XXI
Plasma cortisol concentration in heifers separated frog 
the usual group
(Experiment 2)
Time of the Day (j^
5 ^
0 8.0 0h ' 1 3 .0 0 h ' 1 6.0 0h 19.00h
....  ^
Heifer Pla&ina ccDrtisol c■6iacentration (ng/ml)
('tdeotifi cationne)
Brown 17.3 ^ . 6 12‘;8 ‘ 9.2
Holstein 1U5 1 ^ . 1 7.9 10.9 5.1
\
Fulani » 21 9.7 8 .8 7.3 3.5
---------
Heifers were kept outdoors all day away from the other 
mates, and bled at the time intervals shown in the table.
184
Table XXII
Mean, with standard error, diurnal plasma cortisol 
concentration in heifers
(Experiment 3)
B r e e d
Time of 
-fas Day BROWN • HOLSTEIN*• FULANI 
(Hour ) n = U n = k n = *+
Plasma Clortisol (ng/ml) j<3
7 - 8 6 .8  M 3.9 7*+.2°F
+ 1 . 1 i°-9 6 (23.*+°C)
11.30 7.U U.3 8U°F
+0 .8 +0 .6 (28.8°C)
Z f ....
.15.30 5.0 O I t k.6 91 °F 
+1 . 1 +0.7 +0.9 (32.8°C)
" \ V .
1 8 .3 0 k.k *1 . 2 *+.o 86°F
+0.3 ^o. 6 (30°C)
Heifers were kept outdoors throughout the day and blood
samples were collected at the times indicated in the
table. ^
n = Number of heifers 
Tq = Ambient temperature 
* = Values in Holstein 15*+ were excluded
(sea Table A 37).
!
185
Table XXIII
Circadian plasma cortisol,with the standard error, ip 
heifers of the Brown^ Holstein and Fulani breeds
of cattle
(Experiment h )
Time of the Day (Hour)F  ....
0 7.30-08.00 1 2-1 3 .0 0 16-1 7 .0 0 19-20 .0 0 2 2-2 3 .0 0 0U-05.00
MEAN PLASMA CORTISOL (ng/ml) WITH THE SITANDARD ElffiOR
.—  
Breed 
Brown 1+.6 7.2 % 8 5.0 6 .2 it. 6 
n = 3 +0.5 +0.7 +0.3 + 1 .1 +1 .1+ +0.L
. :..\
Holstein 5.8 6.7 5.3 5.6 5
n = 3 +0 .1 +0.1+ + . 1 + .1+ +1 . 0 +0 .6
........ . ..V
Fulani 6.1+ 5.8 5.3 U . 2 5.0 i+. 5 
5 1 #
n = 3 +0.1+ +0 .6 +1.3 +0.U +0 .6 +0.5 +0 • 6
Plasma cortisol levels were generally low and showed no rhythms.
n = number of heifers.
OO
COVJ1
. r*O
185
Table XXIII
Circadian plasma cortisol,with the standard error,, in 
heifers of the Brown, Holstein and Fulani breeds 
of cattle
(Experiment 4)
Time of the Day (Hour)
07.30-08.00 12-13.00 16-1 7 .0 0 19-20 .0 0 I 2 2 -2 3 .0 0 01 - 02.00 04-05.00
MEAN PLASMA CORTISOL (ng/ml) WITH THE SITANDARD ElffiOR
Breed 
Brown 4.6 7.2 6 .8 1>.5 5.0 6.2 4.6
n = 3 +0.5 +0.7 +0.7 +0.3 + 1.1 +1. h +0.4
T
Holstein 5.8 6.7 5.3 5.6 4.6 5.4
n = 3 +0.1 .0.8 +0.4 + .1 + .4 + 1.0 + 0.6
Fulani '/ 6.4 5.8 5.3 4.2 5 .0 4 .5
n = 3 +0.4 + 0.6 +1.3 +0.4 +0.6 + 0 .5 +0 .6
---- O ----
Plasma cortisol levels were generally low and showed no rhythms.
n = number of heifers.
Fitjtire I s  ft German- srtnm heifer
187
188
Figure 3 A White Fulani haifer
*
189
Percentage monthly weight 
changes: composite of four 
heifers/breed.
t h r ^ h  t F? fr^  consi<5er«d * * * » ■  January i97S
first^r&ln^all^ S !  1  Welryht fM*» was s a l m i  after the
x j T T l T  . !tro  ° April ~ Jtovmbixm  asusmosc- iat*e d« *w<i*t*h«  rsahianrfpa lIln cpreeaaks esl ain
2 L T 1 f l S S L  , l t h  “ “  « * • * * ,
l
190
<b
Flfure 5
191
Mtan environmental temperature and humidit y 
during the periods when physiological stupes on 
heifers were conducted .
r K)0
*
QXL
R e la tiv e  hum idity. (R H 7 .)  
Environmental temperature.
Flgura Si Minimum end maximum environmental temperatures occurred 
at 07.00 and IB.00 hours respectively- the reverse is true for the 
relative humidity. Lowest environmental temperatures and highest 
relative humidities occurred in July - August period, Momingg 
environmental temperatures warn highest and increased most rapidly 
during the March - April period.
MEAN RESPIRATORY RATES AND RECTAL 
TEM PERATURES IN H EIFER S.
AM A M
[ STANDARD DEVIATION.
respiratory rat* ’ ydif f<ir**«** in the 
difference* m  «*** S**Cl«* duerterly
diurnal differentia# In rectal t n i w l ! * sll*ht but significant.
P Mr®8 were also a ig n ific a n t.
193
RECTAL TEMPERATURE : COMPOSITE OF 
5-7 CYCLES/BREED.
OCTOBER -  NOVEMBER.
102-1I  |.  rFuullaannii j
>01
too*
............  ^
ESTROUS CYCLE DAYS. 
 ̂* OVULATtON
££H£li: Examples of mean morning (07 07.30 hour**) root. 
w.a.se mpeevriedteurnsts, through the astro us cycles. No definite rhvthr 
133
RECTAL TEMPERATURE : COMPOSITE OF
5-7  CYCLES/BREED.
OCTOBER -  NOVEMBER.
|  Fulani |
joi-<
i i i i i i n
8 910 11 12 13 -i -3-2 -13 0 1 2  3
t
ESTRUS ESTRUS
ESTROIJS CYCLE DAYS. 
|  * OVULATION
examples of mean morning t07 07.30 hours) rectal 
wtaesm peerviadteunrte.s  through tho estrous cycles. No definite rhyythm 
1M
i ! Chi
fMlMI !■ © £  ̂»US CP
i
* « ■  x s s x « .
^ f T .  t r . n ^  U *  W h i t .  r u l h T i  e n d  « . . .  ' » w n  
gtwacir grazing in the *un.
t
195
flggg. 1°* Panting Holstein heifer. Characteristically, ' 
panting is associated with opened mouth and loss of saliva.
s v
196
PECENTAGE DISTRIBUTION* OF 
TIME OF ONSET OF ESTRUS.
LillyEfLji' eatrua commenced during the day time with a 
greeter concentration In the morning hours and no significant 
hraed difference, n * number of observations.
197
PERCENTAGE DISTRIBUTION OF 
DURATION OF ESTRU S.
t * MEAN
Figure 12 Tha range, of th® duration of ewtrus was sifailar 
irTth# throe breads but mean values differed significantly 
between th® Frowns and th® Fulanis.
PERCENTAGE DISTRIBUTION OT  
ESTROUS CYCLE LENGTH.
30-i
Estrous cycle length (Days), 
t * MEAN.
Figure 13; Mean estrous cycle length was significantly
longer in the Brown and Fuleni than In the Holstein heifers
19S
Plasma cortisol concentration during 
estrous cycles:composite of 4 heifers/ 
breed ( December -  January).
15­ WHITE FULANI
10-
t 1111111111 m 111 n _i 11111 • n
15­
HOLSTEIN
10-
3Z 5-1 11111 ii 111111 11111 n
1io-
. a  T I
15-
BROWN IT
10-
A  ’ \ i / V i
'i-B2 Q i♦ r2 nimrarOTU6 8 10 12 14 r-3* _111 3
Esrrus j
Ovulation—! Ovulat.orw
ijj = Standard error
j S / f c  I S , P*rp f  ”0' t r m  * 1575 through
• hours; and this if - to flgHTM 13. and 1?.
Plasma cortisol concentration during 
estrous cycles: composite of U heifers/
breed ( March-April).
jrfSnr W ?  P*rl°d C° V* r e 0  W,3# faetw*®n ’larch
Plasm a cortisol concentration during 
cstrou s cycles: composite of 
Uheifers / breed ( July — August).
15-1
CilHELl®.1 Ths periodcovered between July 5 and
Plasma cortisol (ng/ml.).
202
Plasma cortisol concentration during 
estrous cycle: Composite of 4 heifers/ 
breed (November 1976).
■uuuiumMimnumn
- 4 - 2  0 * 2  4 6  8 1 0 1 2  -2 01 2 4
f t _ ___  t l _
Estrus 
m Ovulation. J
l  EstrusOvulation. - !
» Days of estrous cycle.
STANDARD ERROR.
throulg*®hp eNrioovde moboevre re1c9f7 8w.as let© October 
203
Mean plasm a cortisol concen­
tratio n  in heifers during four 
periods o f the year.
Determinations made on alternate days during periods indicated 
were plotted. See Table X V I (page 178) for the number of 
observation/breed/quartor.
2m
Diurnal changes in rectal tcm pcrat-
205
DIURNAL CHANGES IN RECTAL 
TEMPERATURES AND RESPIR­
ATORY RATES IN HEFERS 
(Under shade).
92 7 7  68 57  65 8 8 R H 7.
72-5 7 8  85 88 78 77AirTemp. <*F)
208
207
Diurnal plasma cortisol concen 
tration in heifers.
7 3 89 91 90 Air temp.CF).
92 • 70 62 68 RH */.,
Air Temperature s Air Temp(*F).
Identification numbers of animals 
are indicated.
Figure 22
208
Diurnal p lasm a cortisol concen­
tra tion  in heifers.
73 84 90 87 AJR TEMP PF).
T T
15- M«an diurnal plasma cortisol Con tro t ion.________
I----- T
15-30 1830
Time of day (Hrs).
Pig. 23
299
ORCADIAN PLASM A CORTISOL CONCENTRATION 
COMPOSITE OF THREE H E IFERS/BREED .
Figur e  24
Plasma Cortisol ng/ml.
*10
! ---- ------ ------------------------- --
|
PLASMA CORTISOL CONCENTRATION 
AFTER SALINE AND A C T H INJEC­
TIONS.
*
Identification nuabars of
ar* lndlc«?t8d
F^ure 25
i-
PLASMA CORTISOL LEVELS AFTER SALINE 
ACTH INJECTIONS: COMPOSITE OF SIX
i * N
212
Figure 27s Stendlng-for-Mountlng eatrual behaviour 
A White Fulanl heifer being mounted by the PI teaser bull.
213
i
Figur® 2§ . fatwwrt Sign (ta il raising}
h holstsin h »lf«r  on h«et interrupts mounting with 
grazing despit® centtnous pressure from the hull.
Teaser bull
214
REFERENCES
Abilay, T,A,, Johnson, H.D., and Madan, M. (1975).
Influence of environmental heat on peripheral plasma progesterone and 
cortisol during the bovine estrous cycle. J. Dairy Sci. 58 (12): 1836-1840.
Abilay, T.A., Mitra, R. and Johnson, K.D. (1975).
Plasma cortisol and total progestin levels in Holstein steers during 
acute exposure to high environmental temperatures (42 C) conditions. 
J. Anim. Sci. 41: 113-117.
Abraham, G.E. (1974),
Radioimmunoassay of steroids in biological materials.
Acta Endocr. Suppl. 183: 1-42.
Abraham, G.E., Buster, J.E. and Teller, C. (1972).
Radioimmunoassay of plasma cortisol. Anal. Lett. 5(11): 757-765.
Abraham, G.E., Swerloff, R., TulchiOnsikyT, D., and Odell, W.T). (1971). 
Radioimmunoassay of plasma progesterone. J. Endpcr. 32: 619-624.
Adams, W.M., and Wagner, W.C. (1970).
The role of corticoids in parturition. Biol. Reprod. 3: 223-228.
Alle'  n, T.E. (1962). .
A response of zebu, Jersey and zebu x Jersey heifer*, to rising 
temperature with particular reference to sweating.
Aust. J. Agr. Res. 13: 165-179. ~
Alvarez, M.B. , and Johnson, If.D. (1973).
Environmental heat exposure on cattle plasma catecholamine and 
glucocorticoids. J. Dairy. Sci. 56: 189-193.
Amakiri, S.F. (1974).
Anatomical studies of the skin of some tropical and temperate breeds of 
cattle maintained in Nigeria. Ph.D. Thesis. University of Ibadan, Nigeria.
Amble, V.N., Krishman, K.S. and Soni, P.N. (1958).
Age at first calving interval for some Indian herds of cattle. 
Indian J. Vet. Sci. 28: 83-92.
Anderson, J. (1936).
Studies on reproduction in cattle. The periodicity and duration of 
estrus. Emp. J. Exp. Agr. 4: 136-195.
Anderson, J. (1948).
Climate and reproduction in cattle in Kenya. 1st Int. Congr, Anim 
Reprod. Milano 1948, Anim. Breed. Abstr. 18, 548 (1950).
Anderson, J. (1944).
The periodicity and duration of oestrus in zebu and grade cattle. 
J. Agr. Sci. 34: 57.
Andrew, E.L. (1937).
Insemination of cows during one heat period. (Probl. Zirotn. Nos. 134-138) 
Anim. Breed. Abstr. 5: 277, TS 5
Appleyard, W.T., and Cook, B. (1976).
The detection of oestrus in dairy cattle. Vet. Rec. 99: 253-256.
Arije, G.R. , Wiltbank, J.N. and Hopwood, M.L. C'I9“70*
Hormone levels in pre- and post-parturient beef cows. J. Anim. Sci. 
39 (2): 338-343.
Asdell, S.A. (1946).
Patterns of Mammalian Reproduction p. 347. 
Comstock Pub. Assoc., Ithaca, N.Y. (1946).
Asdell, S.A., de Albany** and Roberts, S.J. (1949).
Studies on the oestrous cycle of dairy cattle, cycle length, size of 
cornus luteum,J  yand endometrial changes. Cornell Vet. 39: 389-402.
Bachner, F. (1960).
Die Entwicklung des lebendgewichts weiblicher rinder beira.
Deulschen Fleckvieh (The development of live weight in female 
German Sxiatusaital cattle). Tierzuchter 12: 361-364.
Badreldin, A.L. and Ghany, M.A. (1952),
Adaptive mechanisms of buffaloes to ambient temperature. Nature 170: 
457-458.
Balch, C.C. (1955).
Sleep in Ruminants. Nature 175: 940-941.
Baldwin, D.M. and Sawyer, C.H_ (1974).
Effects of dexamethasone on LH release and ovulation in the cyclic rat. 
Endocrinology^ 94: 1397-1403.
216
Bane, A., and Rajakoski, E. (1961).
Bovine estrous cycle. Cornell Vet. 51 (No. 1): 77-95.
Bassett, J.M. and Hinks, N.T. (1969).
Microdetermination of corticosteroids in ovine peripheral plasma. 
Effects of venipuncture, corticotropin, Insulin and glucose.
J. Endocr. 44: 387-403.
Bassett, J.M. and Thorburn, G.D. (1969). . A
Foetal plasma corticosteroids and the initiation of parturition in sheep. 
J. Endocr. 44: 285-286.
Beakley, W.R. and Findlay, J.D. (1955). A
The effect of environmental temperature and humidity on the rectal 
temperature of calves. J. Agr. Sci. 45: 339-352.
Bergman, R.K. and Johnson, H.D. (1863). 
Temperature effects on plasma cortisol of cattle 
J. Anim. Sci. 22: 854. (A
Berman, A. (1967).
Diurnal and seasonal changes in bovine respiratory functions in a 
sub-tropical climate. Aust. J. Agr. Res. 18: 849-860.
Berman, A. (1968
Nychth ;meral and seasonal patterns of thermoregulation in cattle. 
Aust. J. Agr. Res. 18: 181-189.
Berman, A. and Morag, M. (1971).
Nychthemeral patterns of thermoregulation in high yielding dairy cows 
in a hot dry near-natural climate. Aust. J. Agr. Res. 22: 671-680.
Berman, A. and Volcanl, R. (1961).
Seasonal and regional variations in coat characteristics of dairy 
cattle. Aust. J. Agr. Res. 12(3): 529-538.
Bianca, W. (1959a).
.Acclimatization of calves to a hot dry environment.
J. Agr. Sci. 52: 296-364.
217
Bianca, W. (1959b).
Acclimatization of calves to hot humid environment. 
J, Agr. Sci. 52: 305-312.
Bianca, W. (1981).
Heat tolerance in cattle; Its concents measurement and dependence on 
modifying factors. Int. J, Biometooy, 5: 5-30.
Bianca, W. (1962). A
Tolerance of severe heat and the behaviour of respiratory minute 
volume in cattle. Nature 195: 120S-1209,
Bianca, W. (1S33).
Rectal temperature and respiratory rate as indicators of heat 
tolerance in cattle. J. Agr. Sci. 60: 113-120t
Bianca, W. (1984).
Thermoregulatory responses of the dehydrated ox to drinking cold and 
warm water in a warm environment. Res. Vet. Sci. 5: 75-80.
‘
Bianca, W. (1965). A
Reviews of the progress of dairy science section A. Physiology. 
Cattle in a hot environment. J. Dairy Res. 32: 291-345.
Bligh, J. (1955).
Comparison of rectal and deep body temperature in the calf.
Nature 176: 402-403.
Bligh, J. (1957).
The initiation of thermal polypnea in the calf. 
J. Physiol. 136: 413-419.
Bligh, J. and Lampkin, G.H. (1965).
A comparison of the deep-body temperature of heifers and zebu cows 
recorded continuously by radio-telemetry under similar field conditions. 
J, Agr. Sci. 64: 221-227. •
218
Bond, J., McDowell, R.E., Curry, W.A., and Warwick, E.J. (1960). 
Reproductive performance of milking Shorthorn heifers as affected by 
constant high environmental temperatures. J. Anim. Sci. 19: 1317 (Abstr.).
Bond, J., and McDowell, R.E. (1972).
Reproductive performance and physiological responses of beef females as 
affected by a prolonged high environmental temperature.
J. Anim. Sci. 35: 820-029.
Bonsma, J.C. (1943).
Influence of color and coat cover in adaptability 
Frag. S. Afr. 18: 101-120. <* #
of cattle. 
Bonsma, J.C. (1949).
Breeding cattle for increased adaptability of cattle to tropical 
conditions. J. Agr. Sci. 39: 204-221.
Bonsma, J.C. and Louw, G.N. (19€ a ?
Heat as a limiting factor in animal production.
Biometeorology 2 Part I, 371-382.
*
Booth, M., Dickson, P.F., Gray, C.H., Greenaway, J.M. and Holness, N.J.(1961) 
Protein binding of cortisol in health and in pregnancy. J. Endocr. 23: 25-35
Bottoms, C.D., Roessel, O.F., Rausch, F.D. and Atkins, E.L; (1972). 
Circadian variation in plasma cortisol and corticosterone in pigs and 
mares. Araer. J. Vet. Res. 33: 785.
Branton, C., Hall, J.G., Stone, E.J., Lank, R.B. and Frye, J.D. Jr.(1965). 
The duration of estrus and the length of estrous cycle in cattle in a 
sub-tropical climate. J. Dairy Sci. 40: 628-629.
Brester, J., and Cole, C.L. (1941).
The time of ovulation in cattle. J. Dairy Sci. 24: 111. 
Brodish, A. and Long, C.N.H. (1962).
ACTH - releasing hypothalamic neurohuraor in peripheral blood. 
Endocrinology 71: 298.
219
Brody, S. (1956).
Climatic physiology of cattle. J. Dairy Sci. 39: 715-725.
Brody, S., Comfort, J.E., Kibler, H.H. and Worstell, D.M.(1947). 
Growth and development with Special reference to domestic animals.
LXI Growth and metabolism of beef cattle. Mo. Agric. Exp. Sta. Bull. 
404, 16 pp.
Brown, R. (1963).
Vascular anatomy of the bovine tail. J. Amer. Vet. Med. Ass. 143(11)
1214-1215.
Brown, W.H., Shanklin, Hahff, G.L. and Johnson, H.D. (1969).
Rate of rectal temperature rise as an index of heat sensitivity. : 
Trans. Amer. Soc. Agr. Eng. 12(2): 225-227.
Brunner, M.A., Donaldson, L.E. and Hansel, W. (1969).
Exogenous hormones and luteal function in hysterectomised and intact 
heifers. J. Dairy Sci. 52i 1849-1854.
. « . • ■ •
Burke, C.W. (1973). A  .....
The Adrenal Cortex In Practical Medicine 1st ed. pp. 1-44.
Gray-Mills Publishing Ltd. London.
Caneiro, G.G. 
Razao de sex bezerrors zebus na zona do medio Sao Francisco. 
Minas Gerlas. Sol. Ind. Anem. NS 11: 27-30.
Cargill, B.F., Steward, R.E. and Johnson, H.D. (1962).
Effect of humidity and total room heat on Vapor dissipation of holstein 
Cows at 65°, 8° and 90°F. Mo. Agr. Exp. Sta. Res. Bull. 794, 32 p.
Cekan, S.Z. (1976).
Reliability of steroid radioimmunoassays, p. 48. Acta Universitatis 
Upsaliensis. Abstract of Uppsala dissertation from the Faculty
Pharmacy 14.
»• —
220
Chapman, A.B. and Casida, L.E, (1937),
Analysis of variation of the sexual cycle and some of its component 
phases with special reference to cattle. J. Agr. Res. 54: 417-435.
Clamohoy, L.L. (1952).
A further study of the breeding habits of cattle. 
Phil. Agr. 35: 473.
Chower, I., Conforti , N., and Feldman, S. (1967).
Effects of corticosteroids on hypothalamic corticotropic releasing 
factor and pituitary ACTH content. Neuroendocrinology 2: 193-199.
Chowers, I., Hammel, H.T., Eiseman, J. Abrahams, R.M. and McCann. S.M.(1966) 
Comparision of effect of environmental and preoptic heating and pyrogen 
on plasma cortisol. Amer. J. Physiol. 210: 606.
Christian, J.J. (1984).
Effect of chronic ACTE treatment < m £» turution of intact female mice.
Endocrinology 74: 669-679.
Christison, G.I. and Johnson, H.D, (1972).
Cortisol turnover in heat stressed cows. J. Anim. Sci. 3J5: 1005.
Church, H.R.J. (19 
West Africa: A st of the Environment and the main use of it.
pp. 49-50. iiongnan Group Ltd. London.
Dale, H.E., Ragsdale, A.C. and Cheng, C.S. (1959).
Effect of constant environmental temperature 50 F and 80 F on 
appearance of puberty in beef calves. J. Anim. Sci. 18: 1363-1366.
Dale, H.E., Stewart, R.E. and Brody, S, (1954).
Rumen temperature. 1. Temperature gradient during feeding and 
fasting. Cornell Vet. 44: 368-374.
221
David-West, K.B. (1977).
Dairy development in Nigeria - Prospects and Challenges, Presented at 
the 14th meeting of the Nigerian Vet. Med. Ass. - Lagos. September 1977.
Delacerda, L., Koworski, A. and Migeon, C.J. (1973).
Diurnal variation of the metabolic clearance rate of cortisol,
Effect on measurement of cortisol production rate. J. Clin. Endocrinol 
Metab. 36: 1043-1049.
Dobson, H. and Kanchev, L.N. (1977).
Effect of adrenal stimulation on bovine plasma steroids,
J. Reprod. Fert. 50: 357-358.
Donaldson, I.E. (1968).
The efficiency of several methods for det(ecting oestrus in cattle. 
Aust. Vet. J. 44: 496-498.
Dowling, D.F. (1959).
The significance of the coat in heat tolerance of cattle. 
Aust.'J. Agr. Sci, 10: 744-748.
Ekins, R.P. (1974).
Basic principles and theory (of radioimmunoassay).
Brit. Med. Bull. 30(1): 3-11.
Erb, R.E., Randel, R.D. and Callahan, C.J. (1971).
Female sex steroid changes during the reproductive cycle. 
J. Anira. Sci. 32: 80-106.
Esslemont, R.J. and Bryant, M.J. (1976). 
Oestrous behaviour in a herd of dairy cows. 
Vet. Rec. 99: 472-475.
Estergreen, Jr. V.L., and Venkataseshu, G.K. (1967).
Positive identification of corticosterone and cortisol in jugular 
plasma of dairy cattle. Steroids 10(2): 83-92.
222
Euker, J.S. and Riegle, G.D, (1973). 
Effects of stress on pregnancy in the rat. 
J* Reprod. Fert. 34: 343-346.
Farmer* R*W. and Pierce (1974).
Plasma cortisol determination: radioimmunoassay and competitive protein 
binding compared. Clin. Chem. 20: 411-414.
Farner, D.S. (1961).
Comparative physiology: Photoperiodicity. 
Ann. Rev. Physiol. 23: 71-96.
Farris, E.-J '. (1954). .
Activity of dairy cows during estrus. J. Amer. Vet. Med. Ass. 125: 
117-120.
Fevold, H.R. (1907).
Regulation of the adrenal cortex secretory pattern by adrenocorticotropin. 
Science 156: 1753-1755.
Findla■ y, J.D. (1954). <  .. 
The climatic physiology of farm animals.
Meteor. Monogr. 2(8): 19-29.
Findlay, J.D. and Ingraham, D.L. (1961).
Brain temperature as a factor in the control of thermal polypnea in 
the ox (Bos taurus). J. Physiol. (Lond.) 155: 72-85.
Findlay, J.D. and Robertshaw (1967).
The mechanism of body temperature changes induced by intraventricular 
injection of adrenaline and 5-hydroxytryptamine in the ox (Bos taurus). 
J. Physiol. 189: 329-336.
Frazer, R. and James, V.H.T. (1968).
Double isotope assay of aldosterone, corticosterone and cortisol in 
human peripheral plasma. J. Endocr* 40: 59-72.
223
Gaalaas, K.F. (1945).
Effect of atmospheric temperature on body temperature and respiration 
rate of Jersey cattle. J. Dairy Sci; 23: 555-563*
Gaalaas, R.F; (1947).
A study of heat tolerance of Jersey cows. J; Dairy Sci. 30: 78-80.
Gangwar, P.D., Branton, C., and Evans, D.L. (1965).
Reproductive and physiological responses of Holstein heifers to 
controlled and natural climatic conditions. J. Dairy Sci. 43: 222-227
Garverick, H.A., Erb, R.E., Niswender, G.D. and Chllahan, C.J. (1971). 
Reproductive steroids in the bovine. Ill Changes during the estrous 
cycle. J. Anita. Sci. 32(5): 946-956.
Gemzell, C.A. (1952).
Increase in the formation and e secretion of ACTH in rats following 
administration of oestradiol- obenzoate. Acta. Endocr. 11: 221-228.
Gersimova, A.A. (1940).
Duration of heat and time of ovulation in the cow. 
Anim. Breed. Abstr. 8: 32.
Ghoshal, N.G. and Getty, R. (1967).
Applied anatomy of the sacrococcygeal region of the ox as related to 
tail-bleeding. Vet. Med. Small. Anim. Clin. 62: 255-264.
Gimenez, Von, T. Ender, M.L. and Hoffmann, B. (1974).
Bestimmung von glucocorticoiden in blut voa rind in beziehung zur 
gelbkor perfunktion des physiologischen brustzyklus und bee exogener 
gleucocorticoidzufuh. Deut. Trerarztl. Wochenschr. 81: 29-52.
Gorski, J., Erb, R., Dickson, W.M. and Butler, C.B. (1958).
S o u r c e s  o f  p r o g e s t i n e i n  t h e  p r e g n a n t  . D a i r y  S c i .  4 1 :  1 3 8 0 .
224
Graber, A.L., Givens, J. , Nicholson, W. , Island, B.P. and Liddle D.W,(1965). 
Persistence of diurnal rhythmicity in plasma ACTH concentration in 
cortisol deficient patient. J. Clin, Endocrinol. Metals. 25: 804-807.
Gray, C.H., Greenaway, J.M. and Holness, M.J. (1961).
In Hormones In Blood, p. 439. Gracy, C.H., and Bacharach, A.L. (Ed). 
N.Y. Academic Press.
Guidry, A.J. and McDowell, R.E., -(1966).
Tympanic membrane temperature for indicating rapid changes in body 
temperature. J. Dairy Sci. 49: 74-77.
Guillemin,a -,Dear, W.E. and Liebilt, R.A. (1959).
Nychtheraeral variation in plasma free corticosteroid levels of the rat. 
Proc. Soc. Exp. Biol. Med. 101: 394-395.
Gwazdauskas, F.C. , Thatcher, W.W. and Wilcox, C.J. (1972).
Adrenocorticotropin alteration of bovine peripheral plasma concentrations 
of cortisol, corticosterone and progesterone. J. Dairy Sci. 55: 1165-1169.
Hafez, E.S.E. (1964).
Behavioural thermoregulation in mammals and birds, 
Int. J. Biometeor. 7(3): 231-240.
Hafez, E.S.E., Schein, M.W., and Ewbank, R. (1969).
The behaviour of cattle. In The Behaviour of Domestic Animals
Ed. E.S.E. Hafez, (2nd Ed), pp. 236-295. Lea Pi Febiger, Philadelphia.
\)
Hall, J.G., Branton, C., and STone, E.J. (1959).
Estrous cycles, ovulation time and time of service and fertility of 
dairy cattle in Louisiana. J. Dairy Sci. 42: 1086-1094.
Hales, J.R.S. and Jessen, C. (1969).
Increase of cutaneous moisture loss caused by local heating of the 
spinal cord in the ox. J. Physiol. (Lond) 204: 40p.
s'
225
/
Hales, J.R.S., and Findlay, J.D. (1968).
Respiration of the ox: Normal values and the effects of exposure to hot 
environment. Resp. Physiol. 4k 333-352.
Haarael, H.T., Hardy, J.D. and Fusco, M.H. (1960).
Thermoregulatory responses in hypothalamic cooling in unanesthetised dogs. 
Amer. J. Physiol. 198: 481-486.
Hammond, J. (1927).
The Physiology of Reproduction in the cow. Cambridge University Press. 
Lond. pp. 226.
Hansel, W. (1959).
The estrous cycle in the cow. In Reproduction In Domestic Animals. 
Cole, H.H., and P.T. Cupps Edition, pp. 223. Acad. Press, N.Y.
Hansel, W. and Trimberger, G.W. (1952).
The effect of progesterone on ovulation time in dairy heifers. 
J # Dairy Sci. 35: 65-70.
Hayraan, R.H. and Nay, T. (1961).
Observation of hair growth and shedding in cattle. 
Aust. J. Agr. Res. 12: 513-527.
Heitzmsn, R.J., Adams, T.C. and Hunter, G.D. (1970).
The assay of corticosteroid in plasma of the dairy cow. 
J. Endocr, 47: 133-134,
Heilman, L,, Nakada, F., Curti, J., Weitzman, E.D., Kream, J., 
Roffward, H., Ellman, S., Fukushioa, D.K., and Gallagher, T,F.(197Q). 
Cortisol is secreted episodically by normal man.
J. Clin. Endocrinol. Metabl. 30: 411-422.
Hill, D.H. (1960).
Skin and hair fibre structure in relation to heat tolerance studies 
in cattle. Presented at 3rd Ann. Conf. of the W. Afr. Sci. Ass. 
University of Ibadan.
226
Hiroshige, T, and Sakakura, M. (1971).
Circadian rhythm of corticotropin releasing activity in the hypothalamus 
of normal and adrenalectomised rats. Neuroendocrinology 7: 25-36.
Holder, J.M. (1960).
Observations on the grazing behaviour of lactating dairy cattle in a 
sub-tropical environment. «J. Agr. Sci. 55(2): 261-267.
Hough, W.H., Bearden, H.J. and Hansel, W. (1955).
Further studies on factors affecting ovulation iIn the cows. 
J. Anim. Sci. 14: 739.
Howarth, B. Jr., and Hawk, H.W. (1968).
Effect of hydrocortisone on embryonic survival in sheep. 
J. Anim. Sci. 27: 117-121.
Howland, B.E. (1972).
Effect of restricted feed intake on LH levels in female rats. 
J. Anim. Sci. 34: 445-447.
Howes, J.R., Warnic, A.C. and Hentges, J.F. (1960).
Comparison of different methods for detecting ovulation in cattle. 
Fert. Steril. 11(5): 508-517.
Hudsofl, S., Mull— J< M".t , Whittlestone and Payne, E. (1975). 
Diurnal variatio in blood cortisol in dairy cow.
J. Dairy Sci,'58(1): 30-33.
Hutchinson, H.G. and Mabon, R.M. (1954).
Studies on the environmental physiology of cattle in Tanganyika. 
J. Agr. Sci. 44: 121-128.
Ingraham, D.I. and Whittow, G.C. (1962).
The effect of heating the hypothalamus on respiration in the ox 
(Bos taurus). J. Physiol. 163: 211-221.
227
Ivankov, M.F. (1956).
The tine of sexual activity and ovulation in cows. 
Anim. Breed. Abstr. 24: 251.
James, V.H.T. and Landon, J. (1976).
Hypothalamic-Pituitary - Adrenal Function Tests, pp. 5-35. 
Ciba Laboratories. Horsham, West Sussex, U.K.
Jochle, W. (1972).
Seasonal fluctuation of reproductive functions in zebu cattle,
Int. J. Biometeor. 16(2): 131-144.
Johari, M.P. and Talapatra, S.K. (1957).
Sex maturity and dairy herd and probable causes of delayed puberty. 
Indian J. Vet. Sci. 27: 85-93.
Johnson, H.D. (1978).
Personal communications.
. o
Johnson, H.D. (1965).
Environmental temperature and lactation (with special reference to 
cattle). Int. J. Biometeor. 9(2): 103-116.
Johnson, H.D. (197S5).
World climate and milk production. Int. J. Bioseteor. 20(3): 171-180.
Johnson, H.D., Hahn, H.H., Kibler, M.K., Shanklin, M.K. and 
Edmonton, J.E. (1967).
Heat and acclimatization influence on lactation of Holstein cattle. 
Mo. Agr. Exp. Sta. Res. Bull. 916, 32 p.
Johnson, H.D., Ragsdale, A.C., Berry, I.L. and Shanklin, M.D. (1962). 
Effect of various temperature in humidity combinations on milk production 
of Holstein cattle. Mo. Agr. Exp. Sta. Res. Bull, 791, 27 p.
228
Johnson, H.D,, Ragsdale, A,C., Berry, M.D., Shanklin, and McLarney (1963), 
Temperature-humidity effects including influence of acclimation in feed 
and water consumption of Holstein cattle. Mo. Agr. Exp. Sta. Res.
Bull. 846, 43 p.
Johnsoft, J.I., Jr., Goy, R.W. and Michels, K.M. (1962).
Physiological mechanisms and behaviour patterns Chap. 7 Ihi The Behaviour 
of Domestic Animals, E.S.E. Hafez (ed.), Bailliere, Tindale ft Cox,
London, 139-179.
<?-
Johnston, J.E., Hamblin, F.B,, and Schrader, (1958).
Factors concerned in the comparative heat tolerance of Jersey, Holstein 
and Red Sindhi-Holstein (FI) cattle. J, Anim. Sci. 17: 473-479,
Johnston, J.E., Naelapaa, H. and Frye, J.B. Jr. (1963).
Physiological responses of Holstein, Brown Swiss and Red Sindhi Crossbred 
bulls exposed to high temperaturers and humidities. J. Anim. Sci. 22: 432-436.
Joubert, D.M. (1954).
The influence of winter nutritional depressions on the growth, 
reproduction and production of cattle. J. Anim. Sci. 44: 5-66.
Kajela, G. (..1 973). s '
Adrenal glucocorticoid response to adrenocorticotrophin and plasma 
levels of corticoids, estrogen, and progesterone in the prepartum 
and postpartum dairy cow. M.Sc. Thesis, Univ. Fla. Quoted by 
Shayanfar, F. et al. (1975).
Kale, S.N. (1963).
A study of seasonal variation in the breeding behaviour of Sahiwal cows 
and Murrah buffaloes. Indian Vet. J. 40: 705-711.
Kanchev, L.N., Dobson, H., Ward, W.R. and Fitzpatrick, R.J. (1976). 
Concentration of steroids in bovine peripheral plasma during the oestrous 
cycle and the effect of betamethasone treatment. J. Reprod. Fertil.
48: 341-345.
229
Seay, E.W.J. <1959).
Aa outline of Higerian Vogel at ion 3rd ed, Lagos Fedoral Govt. 
Printer.
Kelly, C.F., Bond, T.E., and Ittner, M.E. (1950).
Thermal design of-livestock shades,' Agr, Bag4 31(19): 601-606,'
Kelly, C.F., Bond, T.E. and Ittner (1957).
Cold spots in the sky may help cool livestock,. Agr* Eng. 38(10) :
726-73Sj
o T
Kendall, S.B. <1943). A ) j ' .
Relationship between breeds of cattle, and ability to maintain a 
constant body temperature under tropical conditions*
Erit. Vet. J. 104: 112-115.
Kendal, J.X. and Lignins, G.C. (1972)..
The effect of dexamethasone on pregnancy in the rabbit.
J. Beared. Fort11. 20: 409-413.
Ki,b ler, H.II. (13§0). &
Oxygen consumption in cattle in relationto rate of increase in 
environmental temperature. Nature 106: 972-973.
Kibler, K.E. (1904.^S0 r
Thermal effects of various temperature-humidity combinations on 
Holstein cattle as measured by eight physiological responses. 
Mo. Agr. Exp. Bta. Res. Bull. 862: 40p.
Kibler, II*E. and Brody, S. (1850^.
Effects of temperature 50 to 105 F and 50 to 90 F on heat production 
and cardiorespiratory activities in Brahman, Jersey and Holstein cows. 
Mo. Agr. Exp. -Sta* Has. Bull. 464: pp. 18.
Kibler, E.E. and Brody, 8 . (1954a)*
Influence of wind on heat exchange and body temperature regulation in 
Jfrsy, Holstein, Brown Swiss and Brahman cattles. Mo. Agr. Exp.
£?ta. Res. Full. 552: pp.39.
m i,
230
Kibler, H.H. and Brody, S. (1954b).
Influence of radiation intensity on evaporative cooling, beat production 
and cardior^ji^^giory activitios ia J4r#e?, K-oistcia and sraimus cows. 
L!o. Agr. Exp. Sta. Res. Bull. 574: pp.31.
Kibler, H.H., Johnson, H.B., Shanklin, M.B^, Hahn, L. (1965). 
Acclimation of Holstein cattle to 04 F (29 F) temperature: 
Changes in heat, producing and heat dissipating functions.
Mo. Agr. Exp. Sta. Res. Bull. 393: pp.28.
Kibler, H.H. and Yeck, R.G. (1959).
Vaporisation rate and heat tolerance in growing Shorthorns,
Brahman, and Santa Gertrudis calves raised at constant 50 and 80 F 
temperatures. Mo. Agr. Exp. Sta. Res. Bull. 701: pp.44.
Kidder, K.E., Barret, G.R. and Casida, L.E. (1952).
A study of ovulations in six families of Holstein-Friesians.
D. Dairy Sci. 35: 43S-444.
Kohli, M.L., and Suri, K.R. (I96j0). f
Breeding season in Mariana cattle: Indian J. Vet. Sci. 30: 219-223. 
Koptowski, J.A. and Tucker, H.A. (1973).
Bovine serum growth hormone, corticoids and insulin during
lactation. Endocrinology 93: 645-651.
Krieger, D.T. (1974).
Circadian pituitary-adrenal rhythms. In: Biological Rhythms. 
Advances In Experimental Medicine and Biology 54: pp. 169-134. 
Hedlund L.W., Franz J.M. and Kenny A.D. (Ed).
Krieger, D.T. (1SS9).
Factors influencing the circadian periodicity of adrenal steroid 
levels. Trans. N.Y. Acad. Sci. 32: 318-329.
Krieger, D.T., Allen, W., Rizzo, F., and Krieger, H.P. (1971). 
Characterisation of the normal pattern of plasma corticosteroid levels. 
J. Clin. Endocrinol. Ketab. 32: 266-284.
231
Krillov, V.S. (1837).
New principle of the organisation and technique of mating cows. 
(Prob. Zirotn No.3, pp.34-42). Anim. Breed. Abstr. j>: 278.
Kriss, M. (1821).
Observations on the body temperature of dry cows.
J. Agr. Sci. 21: 1-28.
Labhsetwar, A.L., Tyler, W.J., Casid, L.E. (1963).
Genetic and environmental factors affecting quiet ovulation in 
Holstein cattle. J. Dairy Sci. XLVI(8): 843-845.
Lauderdale, J.W. (1972). «
Effect o* corticoid administration in-bovine pregnancy. J. Amer.
Vet. Med. Ass. 160(0): 367-871.
Lauderdale, J.W. (1974). o *
Estrus detection and synchronisation of dairy cattle in large herds 
J. Dairy Sci. 57: 348-354.
Lee, B.H.K. (1865). f
Climatic stress indices for domstic animals. Int. J. Bioseteor. 9{
29-35.
Lee, D.H.K. and Phillips, R.W. (1948).
Assessment of the adaptability of livestock to climatic stress.
J. Anim. Sci. 7: 331-425.
Lee, J.A., Roussel, J.D. and Beatty, J.F. (1976).
Effect of temperature season on bovine adrenal cortical function, 
blood cell profile and milk production. J. Dairy Sci. 59: 104-108.
232
Liggins, G.C. (1968).
Prenature parturition after infusion of eorticotrophin or cortisol 
into foetal lambs. J. Endocr. 42: 323-329,
Liggins, G.C. (1963).
Premature delivery of foetal lambs infused with glucocorticoids.
J. Endocr. 45: 515-523.
Linder, H.R. (1964). S
Comparative aspects of cortisol transport: lack of firm 
binding to plasma protein in domestic animals.
J. Endocr. 28: 301-320.
Liptrap, E.M. (1370).
Effect of corticotrphin and corticosteroids on estrus, ovulation and 
estrogen excretion in the cow. J. Endocr. 47: 137-205.
'
Loraine, J.A. and Bell, E.T. (1966).
Corticosteroids. In: Hormone Assays and Their Clinical Application. 
2nd ed. E.S. Livingstone Ltd. Edinburgh and London, pp.439-414.
MacAdam, W.R. and Eberhart, R.J. (1972).
Diurnal variation in plasma corticosteroid concentration in dairy 
cattle. J. Dairy Sci. 55: 1792-1795.
MacFarlane, W.V. (1968).
Adaptation of ruminants to tropics and deserts. In 
Adaptation of Domestic Animals. E.S.E. Hafez (ed) pp.164-182.
Kadan, M.L. and Johnson, E.D. (1973).
Environmental heat effects on bovine luteinising hormone 
J. Dairy Sci. 56(11): 1420-1423.
233
Hajeed, M.A., Oureshi, A.W., and Tayyah, M. (1966).
Seasonal variations in calving frequency in West Pakistan buffoXo 
and cow, and their effoot on reproductive -efficiency.
W. Pakistan J. Agr. Res. 4; 140-15C.
Marple, D.N., Aberle, E.D., Forrest, J.C. Blake, W.E. and Judge, M.B. 
(1972) . Effects of humidity nnd temperature on. porcini plasma 
adrenal corticoids, ACTH, and growth hormone levels.
J. Anin, Sci. 34: 809-812,
Marshall, F.E.A. (1942).
Exteroceptive factors in sexual periodicity. Biol. Revs. 17: 68-90.
Mattingly, D. (1362). V .  V  .
A simple fluoroastric method for the estimation of free 
11-hydroxycorticoids in human plasma. J. Clin. Pathol. 15: 374-379.
i y
?ieBonald, L.E. (1963). 
Veterinary Endocrinology and Repraoduction. Lea & Febiger, Phila.
$
McDowell, R.E. (1966).
The role of physiology in the animal production for tropical and 
sub-tropical areas. World Rev. Anim. Prod. 1: 39-46.
McDowell.,, R.E., £McDaniel, B.T., Barrada, M.S. and Lee, D.E.K. (1961), 
Rate of surface evaporation from the normal body surface and with 
sweat glands inactivated under hot conditions. J. Anim. Sci.
20(2): 389-395.
McDowell, R.E. and Johnson, J.E. (1971).
Research under field conditions. In: A guide To Environmental Researc'- 
Qn Animals. Natl. Acad. Sci. Washington, D.C. 1S71, 306-360.
McDowell, R.E., Lee, B.K.K., Fohrnan, M.H. and Anderson, R.S. (1953). 
Respiratory activity as an index of heat tolerance in Jersy and Sindhl 
x Jersey (Fi) crossbred cows. J. Anim. Sci. 12: 573-581.
234
McDowell, R.E., Lee, D.H.K., Fohrman, M.H., Sykes, J.F. and Anderson, R.A. 
(1955). Rectal temperature and respiratory rates of Jersy and 
Sindhi-Jersey (Fri) crossbred females to standard hot atmosphere.
J. Dairy Sci. 38: 1041-1045.
McLean, J.A. (1963).
The partition of insensible losses of body weight and heat from cattle 
under various climatic conditions, j. Physiol. 167: 427-447.
McLean, J.A. and Calvert, D.T. (1972).
Influence of air humidity on the partitioning of heat exchange of 
cattle. J. Agr. Sci. 78: 303-314.
McNarthy, K.P. and Thurley, D.C. (1973).
The episodic nature of changes'in ovine plasma cortisol levels and 
their response to adrenaline during adaptation to a new environment. 
J. Endocr. 59: 171-180.
Melarapy, R.M., Hearn, W.R. and Rakes, J.M. (1959). £
Progesterone content of bovine reproductive organs and blood during 
pregnancy. J. Anira. Sci. 12: 307-313.
Migeon, C.J., Tyler, F.H., Mahoney, J.P., Florentin, A.A., Castle, H., 
Bliss, E.L., and Samuels, L.T. (1956).
The diurnal variation of plasma levels and urinary excretion of 
17-hydroxycorticosteroids in normal subjects, night workers and blind 
subjects in man. J. Clin. Endocrinol. Metab. 16: 622-633.
Miller, E.L. and Allison, C.W. (1974).
Plasma corticoids of Angus heifers in programmed circadian temperatures 
of 17 to 21C and 21-34C. J. Anim. Sci. 38(4): 819-822.
Moberg, G.P. (1976).
Effects of environmental and management stress on reproduction in the 
dairy cow. J. Dairy Sci. 59: 1618-1624.
235
Monty, Jr., D.E. and Wolff, L.K. (1974), .
Summer heat stress and reduced fertility in Hoistein-Friesian cows 
in Arizona. Araer. J. Vet. Res, 35: 1495-1500.
Moray, M. (1967):
Influence of diet on the behaviour pattern of sheep.
Nature 213; 110.
Moran, J.B. (1970):
Seasonal and diurhal variations in body temperature of Hereford and 
Brahman cross cattle in a cool temperature environment.
J. Agr. Sci. (Camb) 74: 205-207.
Murphy, B.E.P. (1967)
Some studies of the protein binding of steroids and their application 
to the routine micro -and ultra micro -measurement of various steroids 
in body fluids by competitive protein-binding radioassay.
J. Clin. Endocrinol. 27: 973-990j
Murray, D.M. (1966):
A comparison of cutaneous evaporation rates in cattle exposed to heat 
in a climate laboratory and in the field.
J. Agr. Sci. 66: 175-179.
Mullick, D.N. (1960):
Effect of humidity and exposure to sun on the pulse rate, 
respiration rate, rectal temperature and haemoglobin level in 
different sexes of cattle and buffalo. J. Agr. Sci. 54(3): 391-194.
Nay, T. (1959):
Sweat gland in cattle, histology, morphology and evolutionary trends. 
Aust. J. Agr. Res. 10: 121-128.
Nay, T. and Hayman, R.H. (1963):
Some skin characteristics in five breeds of European (Bos taurus) 
dairy cattle. Aust. J. Agr. Res. 14(2): 294-302.
Nazareno, L.E. (1954):
Additional c'ata on the breeding habits of Red Sindhi cattle.
Phil. Agr. 3.: 339.
236
Nelson, D.H. and Samuel, L.T. (1952):
A method for the determination of 17-hydroxycorticosteroids in 
blood: 17-hy<4r<?)(ya>rticosterone in the peripheral circulation. 
J. Clin. Endocrinol. Metab. 12: 519-526.
Nieschla r, E., and Wickings, E.J. (1975):
A review of RIA of steroids, 2. Klin, Chem. Klin. Biochem.
13 Jahrg Heft 7: 261-271,
Ojo, 0. (.1971) :
Bovine energy balance climatology and livestock potential in Nigeria. 
Agr. Metecr. 3: 353-369.
Ojo, 0. (1973):
The distribution of solar and net heat load on cattle in Nigeria. 
J, Trop. Geogr. 36, 50-59.
Olusanya, C. (1976):
Department cf Veterinary Physiology, University of Ibadan, Nigeria 
(Personal c<mmunication).
Oyenuga, V.$. and Olubajo, P. (1966):
Productivity and nutritive value of tropical pastures at Ibadan. 
Pro.c. Int. Congr. Grassland, 10th, Helsink 1966 pp 36.
Ccrticosteroads,circulating leukocytes, and erythrocytes in Cattle; 
Diurnal Chances and effects of bacteriological status, stage of 
lactation, ar.d milk yield on response to adrenocorticotropin.
Ame.1*. J. Vet. Re-. 35: 355 - 362.
Paape, M . ghynes, W.F., Guidry, A.J., Desjardins, C., and
Miller, C. (1 -73) :
Adrenal and red blood cell response to ACTH during 32 C stress .
J. Anim. Sci. 37: 249 (Abstr.).
Panaretto, B.A. and Vickery, M.R. (1970):
The rates of plasma cortisol entry and clearance in sheep before and 
during their exposure to a cold wet environment. J. Endocr. 47: 
273-285.
237
Paschkis, K.E., Cantarow, A., Walkling, A.A , and Boyle, D. (1950),; 
Adrenal cortical hormone levels in. adrenal vets* nnrj peripheral 
blood. Endocrinology 47: 338-346.
Paterson, J.Y.F. (1957):
17-hydroxycorticosteroids and leucocytes in the blood of dairy 
cattle. J. Comp. Pathol. Ther. 67: 165.
Perkoff, G.T., Eik-Nes, K., Nugent, C.A., Fred, H.L., Nimer, R.A., 
Rush, L., Samuels, L.T., and Tyler, F.H, (1959):
Studies of the diurnal variation of plasma 17-hydroxycorticosteroids. 
J. Clin. Endocrinol. Metab. 16: 432-443
Phillips, R.W. (1949):
Breeding livestock adapted, to unfavourable mts • r , 
II Adaptability of cattle to tropical and « ical climates.
FAO Ag*• Stud. No. 1, pp 67-103.
Plasse#.D., Warnick, A.C., and Roger, M. (1968):
Reproductive behaviour of Bos indicus females in a subtropical 
environment. 1. Puberty and ovulation frequency in Brahman and 
Brahman x British Heifers. .
J. Anim. Sci. 27(1): 94-100.
Plasse, D. Warnick, A.C., and Roger, J. (1970):
Reproductive behaviour of Bos indicus females in a subtropical 
environment. IV. Length of estrous cycle, duration of estrus, time 
o'f ovulation, fertilization and embryo survival in grade 
Brahman heifers.
J. Anim. Sci. 30: 63-72.
Pollar, I., Basset, J.R. and Caincross, R.D. (1976):
Plasma glucocorticoid elevation and ultrastructural changes in the 
adenohypophysis of the male rate following prolonged exposure to 
stress. ^tNeewurooerndocrinology 21: 312.-330.
Poston, H.A., Ulberg, L.C., and Legates, J.E. (1962):
Analysis of seasonal fluctuations of reproductive performance of 
dairy cows.
J. Dairy Sci. 45: 1376-1379.
238
Quazi, F.R. and Shrode, R . R .  (1954):
Variation in rectal temperature, pulse rate and respiratory rate of 
cattle as related to variation in four environmental variables.
J. Anim. Sci. 13: 1028-1029.
Quinlan, J., Bisschop, J.H.R. and Adelaar, T.F. (1941):
Bionomic studies on cattle in the semi-arid region of the union 
of South Zifrica. IV - The ovarian cycle of heifers during summer. 
Onderstepoort J. Vet. Sci Anim. Ind. 16(1 & 2) :
213-241.
Quinlan, J. and Roux, L.L. (1936):
Research into sterility of cows in South Africa.
Onderstepoort J. Vet. Sci. Anim. Ind. 6: 719
Rainey, J. Johnston, J.E. and Frye, Jr. J.Bv. (1967):
Effects of solar radiation and ration on certain physiological 
and productive responses of Holstein cows.
J. Dairy Sci. 50(6): 966 (Abstr.)
Rakha, A . M .  and Igboeli, G. (1971):
Effect of nutrition, age and season on estrous cycle in indigenous 
Central African cattle.
J. Anim. Sci. 32: 943-945
5 - o
Rakha, A.M. Igboeli, G. and Hale, D. (1970):
The estrous cycle of zebu and sanga breeds of cattle in Central 
Africa. J. Reprod. Fert. 23: 411-414.
Handel, R.D., and AEprbb, (1971)
Reproductive steroids in the bovine. VI Changes and inter­
relationships from 0 to 260 days of pregnancy.
J. Anim. Sci. 33(1): 115-123.
x Ray P.D.,(1968):
Adrenal glucocorticoids and gluconeogenesis. In:Functions o f  the 
Adrenal Cortex. K. W. Mckerns (ed), 2: 1137, Appleton-Century 
Crafts, New York.
Ragsdale, A..C., Thompson, H.J., Worstell, D.M. and Brody, S. (1950) 
Milk production and feed and water consumption responses of Braha 
Brahman Jersey and Holstein Cows to changes in temperature 50-105 
and 50-80°F.
Mo. Agr. Exp. Sta. Res. Bull 460; pp. 28.
239
Reynolds, W.L., DeRouen, T.M. and High Jr. W.J. (1963):
Age and weight at puberty of Ahgus, Brahman and zebu cross heifers. 
J. Anim. Sci. 22: 243 (Abstr.).
Rhoad, A.' (1936):
The influence of environmental temperature on the respiratory 
rhythm of dairy cattle in the tropics.
J. Agr. Sci. 26: 36.
Rhoad, A.O. (1938):
Some observations on the response of purebred Bos taurus and Bos 
indicus cattle and their crossbred types to certain conditions of 
the environment. Proc. Amer. Soc. Anim. Prod. 31st Meeting pp
284 - 295.
Rhoad, A.O. (1944):
The Iberia heat tolerance test for cattle.
Trop. Agr. (Trin.) 21: 162-164.
Rhoad, A.O. (1940 ):
Absorption and reflection of solar diation in relation to coat 
colour in cattle. Proc. Amer. Soc. Anim. Prod. pp. 291 - 293.
Rhoad, A.O. (1940b):
A method of assaying genetic differences in adaptability of cattle 
to,tropical climate. Emp. J. Exp. Agr. 8: 140.
Rhynes, W.E. and Ewing, L.L. (1973):
Plasma corticosteroids in Hereford bulls exposed to high ambient 
temperature. J. Anim. Sci. 36: 369-373.
Riejner schmid. G. (1943) ;
Sane aspects of radiation in its relation to cattle in South 
Africa and Europe. Onderstepoort. J. Vet. Sci. Anim. Ind. 19
(1 & 2) 327 - 353.
Riemerschmid G and Elder J.S. (1945)
The absorptivity for solar radiation of different coloured hairy 
coats of cattle.
Onderstepoort. J. Vet. Sci. Anim. Ind. 20(2): 223-233.
240
Riek, R.F. and Lee, D.H.K. (1948):
Reactions of Jersey calves to hot atmospheres.
J. Dairy Res. 15: 227-232.
Riek, R.F. and Lee, D.H. (1948):
Reactions to hot atmospheres of Jersey cows in milk. 
J. Dairy Res. 15(3): 219-226.
Richards, P.H.(1946):
Observations on the reproduction of zebu cattle in southern Nigeria 
dairies. Trop. Agr. (Trin.) 23: 103-108.
Roberts, S.J. (1971):
Physiology of female reproduction. In: Veterinary Obstetrics and 
Genital Diseases. 2nd ed. Ithaca N.Y. 343-375.
Robertson, W.G. and Mixner, J.P.
Chemical determination of 17-hydrc rticosteroids in the blood of 
cattle and some indications of it ysiological significance.
J. Dairy Sci. 39; 589-597.
Robinson, K.W. and Lee, D.H.K. (1947):
The effect of nutritional plane upon the reactions of animals to heat. 
J, Anim. Sci. 6: 182-194.
Robinson, K.W. and Morris, L.R. (I960):
Adrenal cortical activity in sheep as measured by urinary 17-ketogenic 
steroid excretion.
Aust. J. Agr. Res. 11:236-246.
Rodbard, D., Ranford, J., Cooper, A., and Ross, G.T. (1968): 
Statistical quality control of radioimmunoassays.
J. Clin. Endocrinol. 28: 1412-1418.
Rogerson, A. (1960):
The effect of environmental temperature on the energy metabolism 
of cattle.
J. Agr. Sci. 55: 359-363.
Rollinson, D.H.L. (1955):
Estrus in zebu cattle in Uganda. Nature 176: 352-353.
241
Rollinson, D.H.L. (1962);
Physiology of reproduction in doaestic animals with special reference 
to African conditions. Bull. Epiz. Dis. Afr. 10: 137-160.
Romance-Pounce, H., Thatcher, W.W., Buffington, D.E., Wilcox, C.J. 
and Van Horn, H.H. (1977):
Physiological and production responses of dairy cattle to a shade 
structure in a subtropical environment.
J. Dairy Sci. 60: 424-430.
Ruder, H.J., Guy, R.L., and Lipsett, M.B. (1972):
A radioimmunoassay for cortisol in plasma and urine.
J. Clin. Endocrinol Metab. 35: 219-224.
Saba, N. (1964):
The estimation of cortisol and cortisone in bovine and ovine plasma. 
J. Endocr. 28: 139-148.
Salisbury,' G.W. and Vandermark, N.L. (1961):
Physiology of reproduction and artificial insemination of cattle.
W. H. Freeman and Co. pp 18-101.
Salmenpera, M. and Kahri, A.I. (1976):
Corticosterone, 18-OH-Deoxycorticosterone, deoxycorticosterone and 
aldosterone secretion in tissue culture of foetal rat, a&reaols in 
the presence and the absence of ACTH. Acta Endocr. 83: 781-793. .
Sandberg, A.A. and Slaunwhite, W.R. (1959) :
Transcortin: a corticosteroid binding protein of plasma.
II Levels in various conditions and the effects of estrogen.
J. Clin. Invest. 38: 1290.
Sandberg, A. and Slaunwhite, JR. W . R .  (1975):
Adrenal corticosteroids (other than aldosterone) in the human: their 
secretions, determination, levels, and use in functional tests.
In: Steroid Hormones. R. I. Dorfman Ed., North Holland Publ. Co.
Saror, D. and Coles, E.H. (1973):
The blood picture of White Fulani (zebu) and White Fulani x Friesian 
(crossbred) dairy cows. Bull. Epiz. Dis. Afr. 21: 485-487.
Satterlee, D.G., Rousel, J.D., Gomila, L.F. and Segura, E.T.
Effect of Exogenous Corticotropin and climatic conditions on 
bovine a<3renal V.ortical function. U  f)airg Sc,. : /t/2.
242
Schein, M.W., McDowell, R.E. , Lee, D.H.K. and Hyde, C.E. (1957): 
Heat tolerance of Jersey and Red Sindhi-Jersy crossbred in 
Louisiana and Maryland. J. Dairy Sci. 40: 1405-1415.
Seath, D.M. and Miller, G.D* (1946):
Effect of warm weather on grazing performance of milking cows. 
J. Dairy Sci. 29:'199-206.
.Seath, D.M. and Miller, G*D* (1947) :
Heat• tolerance comparison between Jersey and Holstein cows.
J. Anim. Sci 6: 24-34.
Seiden, G. and Brodish, A. (1972 
Persistence of a diurnal rhythm 
of hormone feedback. Endocrinol _
Shafie, M.M. and El-Tannikhy, L.M. (1970).
Comparative study of skin structure in Egyptian and imported 
cattle breeds and their crosses in relation to heat tolerance. 
UAR. J. Anim. .’Prod. 10: 115-131.
Shaw, K.E. and Nichols, R.E. (1963): .. .
The influence of frequent blood sampling of calves upon their response 
to exogenous adrenocorticotropic hormone.
Amer. J. Vet. Res. 24(100): 565-566,
Shaw, K.E., Dutta, S. and Nichols, R.E. (1960):
Quantities of 17-hydro^corticosteroids in plasma of healthy cattle, 
during Amer. J. Vet. Res. 21(80):
52-53.
Shayanfar, F., Head, H.E., Wilcox, C.J., and Thatcher, W.W. (1975): 
Adrenal responsiveness in lactating Holstein cows.
J. Dairy Sci. 58: 870-878.
Shrode, R.R., Ouazi, F.R., Rupel, I.W., Leighton, R.E. (I960): 
Variation in rectal temperature, respiratory rate and pulse rate 
of cattle as related to variations in 4 environmental variables. 
J. Dairy Sci. 43(9): 1235-1244.
Siegler, S.L. and Siegler, A.M.(1951):
Evaluation of the basal body temperature.
Fert. Steril. 2: 287-301.
243
Slaunwhite, W.R. Jr., Lokie, G.N., Rack, N., and Sandberg, A. A. (1962): 
Inactivity invivo of transcortin-bound cortisol. Science 135:
1062 - 1063.
Smirnova, E.J. (1953)
Teaperwturnaja reaka ja kak pokaz^tel 'srreraeni ovuljucii u korov. 
(Temperature reaction as indicating time of ovulation in cows)
Dokl Akad. Seljskohoz Nauk, Lenin; 18(8): 44-48. Anim. Breed. Abstr. 
22: 316(1954).
Snedecor, G.W. and Cochran, VJ.G. (1967) :
Statistical Methods. 6th ed. pp 59-60, 62, 172-195, 258-296,
339-346. £ ovucl estate Uni v. P r e s s , p t r ^ & S .
Sprague, E.A., Hopwood, M.L.,Niswender, G.D., artd Wiltbank, J.N.(1971): 
Progesterone and LH levels in peripheral blood of cycling beef 
cows. J, Anim. Sci. 33(1): 99-103.
Steinbach, J. and Balogun, A. A. (1971):
Seasonal variations in the conception rate of beef cattle, in the 
seasonal equatorial climate of southern Nigeria,
Int. J, Biometeor. 15(1): 71-79,
Stott, G.H., (1961):
Female and breed associated with seasonal fertility in dairy cattle. 
J.. Dairy Sci. 44: 1698-1704.
Stott, G.H. (1972): Climatic thermal stress. A cause of hormone 
depression and low fertility in bovine. Biometeor. 5: 113 
(Abstr.).
Stott, G.H. and Robinson, J.R. (1970):
Plasma corticosteroids as indicators of gonadotrophin secretion 
and fertility in stressed bovine.
J. Dairy Sci. 53: 652(Abstr.).
Stott, G.H., Thomas, M.R. and Glenn, L.W. (1967): 
Blood progesterone in thermally stressed bovine. 
J. Dairy Sci. 50: 966 (Abstr.).
Stott, G.H. and Wiersma, F» (1971):
Plasma cortiCoids as an index of acute and chronic environmental stress. 
Presented at First Conf. Biometeorol and 10th Conf. Agr. Meteor. 
Columbia, MO.
244
Stott, G.H. and Williams, R.J. (1962)2
Causes of low breeding efficiency in Dairy cattle associated 
with seasonal high temperature. J. Dairy Sci. 45: 1369-1375.
Swanson L.V. and Eafs, H*D. (1971).
L.H. and prolactin in blood serum from estrus to ovulation in 
Holstein heifers. J. Anim. Sci. 33(5): 1038 - 1041.
Swanson, L.V. Hafs, H.D. and Morrow, D.A. (1972):
Ovarian characteristics and serum LH, prolactin, progesterone 
and glucocorticoids from first estrus to breeding size in Holstein 
heifers. J. Anim. Sci. 34: 284-293. a -
Takebe, K., Sakakura, M., and Mashimo, K. (1972):
Continuance of diurnal rhythmicity of CRF activity in hypophysectomised 
rats. Endocrinology 90: 1515-1520.
Taneja, G.C. (I960):
Sweating in Cattle. VI Density of swea t gland and its relationship
with cutaneous evaporation.
J. Agr. Sci. 55: 104-110.
Thatcher, W.W. (1974):
Effects of season, climate, and temperature on reproduction and 
lactation. J. Dairy Sci. 57: 360-368.
Thibault, C., Courot, M., Martinet, L., Mauleon, P., Du Mesnil 
Du Buisson, L. Ortavant, R., Pelletier, R. and Signoret, J.P. (1966) 
Regulation of breeding season and estrous cycles by light and 
external stimuli in some mammals. J. Anim. Sci. 25, (Suppl.): 
117-139.
< s r
Thibault, C. and Levasseur, M.C. (1975):
Reproduction in Farm Animals. Ed. E.S.E. Hafez, 3rd Ed. pp 82-100.
Lea and Febiger, Phila.
Thompson, G.E. (1973):
Review of the progress of Dairy Science. Climatic, physiology of 
cattle. J. Dairy Res. 1973, 40, 441-473.
Trimberger, G.W. (1948):
Breeding efficiency in dairy cattle from artificial insemination at 
various intervals before and after ovulation.
Nebr. Agr. Exp. Sta. Res. Bull 153, p. 26.
245
Trioberger, G.W. (1956):
Ovarian function, Intervals between estrus and conception rates in 
dairy cattle. J. Dairy Sci. 39: 448-455.
Taimberger, G.W. and Hansel, W. (1955) :
Conception rate and ovarian function following estrus control by 
progesterone injections in dairy cattle.
J. Anim. Sci. 14: 224.
Turner, C.D. and Bagnara, J.T.
General Endocrinology, 5th ed. pp 348-386. Saunder Co. Phila. 
Ulberg, L.C. (1958):
The influence of high temperature on repr ion.
J. Hered. 49: 62-64.
Van der Westhuysen, J.M. and Venter, J.A. (1976):
Some factors affecting fertility in dry cows in Southern Aftlcgu
S. Afr. J. Anim. Sci. 4: 185-189.
Vanjonack, W.J. and Johnson, H.D. (1975):
Effect of heat and milk yield on bovine plasma glucocorticoid-levels. 
Proc. Soc. Exp. Biol. Med. 148: 970-973.
Vap Rensburg, S.J.W. and de Vos, W.H. (1962):
Ovulatory failure in bovines.
Onderstepoort J. Vet. Res. 20: 55-79.
Venkataseshu, G.K. and Estergreen, Jr. V.L. (1970):
Cortisol and corticosterone in bovine plasma and the effect of 
adrenocorticotropin. J. Dairy Sci. 53: 480-483.
Vescei, P. (1974) .
Methods of Hormone radioimmunoassay, pp 393-415. Bernard M. Jaffe 
and Behrman H.R. Acad. Press, N.Y. 1974.
Villacorta, Vasquez de Valazo (1960):
The estrous cycle, duration of heat and time of ovulation in cattle in 
the tropics. Anim. Breed. Abstr. 29: 52.
Vincent, C.K. (1972):
Effects of season and high environmental temperature on fertility 
in cattle. A review. J. Amer. Vet. Med. Ass. 161(11):1333-1338.
246
Vogt; H. (1943):
The output of cortical hormones by the mammalian suprarenal. 
J. Physiol. 102: 341-356.
Vollan, R. and Vollan, U. (1942):
Teaperaturunterschungen zur reproducktionphysiologie der Iran 
und der 3cuh Schweiz. Arch. Tierheik, 84: 403. (Quoted by Wrenn
et al 1958).
Wagner, W.C. and Oxenreider, S.L. (1972):
Adrenal function in the cow. Diurnal changes and the effects of 
lactation and neurohypophyseal hormones. J. Anim. Sci. 34: 630-635.
Wagner, Strohben, R.F. and Harris, P.A. (1972): 
ACTH corticoid s and luteal function in heifers.
J. Anim. Sci. 35: 789.
Wagnon, K.A., Rollins, V?.C., Cupps, P.T. and Carroll, F.D. (1972): 
The effects of stress factors on the estrous cycles of beef heifers 
J. Anim. Sci. 34(6); 1003-1010.
Waites, G.M.H. (1976):
Temperature regulation and fertility in male and female mammals. 
Israel J. Med. Sci. 12(9): 982-993.
Walker, C.A. (1957):
Studies of the cattle of Northern Rhodesia. The apocrine gland 
population of the skin of Northern Rhodesia cattle and its connection 
with the beat tolerance coefficient. J. Agr. Sci. 49: 401-404.
Whipp. 5.Co and Lyon, II. C. (1970);
Hydrocortisone determination bovine plasma.
Cornell Vet. 60: 582-589.
Wiersma, F. and Stott. G.H. (1969):
New concepts in the physiology of heat stress in dairy cattle of 
interest to engineers. Trans Ataer. Soc. Agr. Eng. 12: 130-132.
Williamson, N.B., Morris, R.S., Blood, D.C. Cannon, C.M. and 
Wright, P.J. (1912).
A study of oestrous behaviour' and oestrus detection methods in 
a large commercial dairy herd. Vet. Rec. 91: 58-62.
William, J.S., Shrode, R.R., Leighton, "Rupel, I.W. (1960):
h A study of the influence of solar radiation on physiological 
responses of dairy cattle. J. Dairy Sci. 43: 1245-1254.
Wilson, S.G. (1946):
Hie seasonal incidence of calving and of sexual activity in zebu cattle 
in Nyasaland. J. Agr- Sci. 36: 246-257.
247
Wilson, W.O., Johnson, H.D,, and Pace, N. (1971):
Physiological functions and measurement techniques. In:
A Guide To Environmental Research On Animals.
Natl.' Acacf. Sci.'" Washington, D. C. pp ^3-l&8.
Wiltbank, J.N., Cook, A.C., Davis, R.E. and Warwick, E.J. (1957): 
The effect of different combinations of energy on occurrence of 
estrus, length of estrous period and time of ovulation in beef 
heifers.
J. Anim. Sci. 16: 1100 (Abstr.).
Wiltbank, J.N., Rowden, W.W., Ingalls, J.E., Gregory, K.I., and 
Koch, R.M. (1962)
Effect of energy level on reproductive phenomena of mature 
Hereford cows. J. Anim. Sci, 21: 219-225.
Wolff, L.K. and Monty, D.E. Jr. (1974):
Physiological response to intense summer heat and its effect on 
the estrous cycle of non-lactating and lactating Holstein cows 
in Arizona.
Amer. J, Vet. Res. 35: 187 - 192.
Worstell, D.M. and Brody, S. (1953):
Comparative physiological reactions of European and Indian 
cattle to changing temperature.
Mo.. Agr. Exp. Sta. Res. Bull 515.
Wrenn, T.R., Bitman, J., and Sykes, J.F. (1961): 
Diurnal patterns of bovine body temperature.
J. Dairy Sci. 44: 2077-2080.
Wrenn, T.R., Bitman, J. and Sykes, J.F. (1958):
Body temperature variations in dairy cattle during estrous cycle 
and pregnancy. J. Dairy Sci. 41: 1071-1076.
Yates, F.E., Leenan, S., Glenister, D.W. and Dallman, M.F. (1961): 
Interaction between plasma corticosterone concentration and 
adrenocorticotropin-releasing stimuli in the rat: Evidence for 
the reset of an endocrine feedback control. Endocrinology 69: 67-80.
Yeates, N.T.M. (1956):
Influence of nutrition state on the heat tolerance of cattle. 
Nature 178: 702-703.
Yousef, M.K. and Johnson, H.D. (1967):
Calorigenesis of cattle as influenced by hydrocortisone and environ 
mental temperature. J. Anim. Sci. 26: 1087-1093.
248
APPENDIX
Test of reliability of radioimmunoassay of cortisol
Fairly proportional increases in cortisol level were found when 
increasing volumes of a plasma sample were extracted and assayed 
(table Al)? but there was a tendency for large volumes (0.6ml) to give 
lower values per milliliter of plasma than expected. The efficiency 
of extraction was the same when twenty volumes of solvent was used 
for the extraction of the larger plasma volumes (0.4 - 0.6 ml) . Most 
of the assays were run using 0.2ml of plasma because better duplicate 
values were obtained than when 0.1m! of plasma were used,, and because 
some values fell below the detection level of the chosen standard 
curve when the latter volume was used. The water blank gave zero 
values, that is, the values were far below the detection level of 
the standard curve most of the time.
The recovery of tritiated cortisol added to plasma was determined. 
Tritiated cortisol (10,000 d.£>.m.) was dried in test tube? 0.2ml plasma 
was added and warmed for 10 minutes at 45°Cf in the water bath and 
then mixed for 30 seconds on the vortex mixer. After allowing to stand 
for 20 minutes, the samples were extracted. The extracts were dried 
at 37°C in counting vials sunder nitrogen and then taken up in 0.5ml 
of assay buffer. The same amount of tritiated cortisol added directly 
to counting vials was dried and taken up in 0.5ml of assay buffer.
After adding scintfliant, the radioactivity was counted in every vial.
249
The recovery varied between 74.5 and 86%; "the mean with standard error
. "St
being Go.l +1 . 0  par cent in a total of 18 determinations carried 
out in six different investigations.
The recovery was checked with each bottle of extraction solvent 
opened and from time to time with each assay. The mean recovery gave 
a correction factor of 1.25, Because of the fairly high precision of 
recovery, it has not been n e c e s s a r y  to incl. udue tLritiated cortisol as 
internal standard in the assays.
Increasing quantities of non-radioactive cortisol v/ere dried in­
test tubes and taken up in 0.2ml of water. Cortisol was* extracted
and assayed? mean percentage of sol recovered ranged from 84 -
99.8 (Table A 2). In 20 different assays, the mean level of cortisol 
recovered in aqueous solutions of cortisol, 5 ng/ml, and lOng/ml, were 
5.69 (+0.19 S.E.) and 9.97 (+0.17) ng/ml with coefficients of variation
of 15 and 8 respectively (table A 3)•
Precision of assay was determined by finding the intra- and inter- 
assay variance bv using the method of Abraham et al (1971). Measurements 
of the same samples in the same assay and in two different assays were 
done in duplicates. The coefficient of variation (CV) of the results 
of duplicate determination from their means was estimated by the following 
formula
CV !ia 2
2n
 ̂ where d s highest value of each duplicate 
lowest value of same duplicate _ 
n » number of duplicate determinations
250
For intra-assay variation, 12 duplicate determinations performed in 
the same assay with values ranging from 1.6 - 18.5 ng/ml had a coefficient 
of variation of 12.3^ (Table A 4). For the inter-assay variation each 
of the groups of 10 and 9 different samples were assayed twice and the 
coefficients of variation were 14.9 and 18.5 respectively (Table A 5).
The plasma pool run with the samples yielded a mean with standard error 
of 7.9 + 0,2 ng/ml in 22 assays with a coefficient of variation of 
10.4/°. The reproducibility of the assay was fair as judged by the 
interwassay variation. The recovery of cortisol added to plasma 
known to contain low levels of cortisol was also used to evaluate 
accuracy. 1, '2, aid 4 ng of standard cortisol were dried in sets of 
tubes and were taken up in 0.2 ml of plasma. After extraction, assay 
and correction of assay value with recovery factor, the mean recoveries 
were 104, 110, and 98 per cent in the tubes containing 1, 2 and 4 
nanograms of cortisol respectively (Table A 6).
The present method was used in participation with an RIA quality 
control programme arranged by the World Health Organisation (Geneva). 
There was close agreement in the value obtained with the present method 
and the mean of results from all the laboratories involved (table A 7 ).
The binding of tritiated cortisol at each level of the standard 
curve expressed as a percentage of the bound tritiated cortisol at zero 
concentration of the non-radioactive cortisol was fairly consistent 
through the assays (Table A 8). The mean (with the standard error) 
value of the slope of the standard curves drawn from the logit - log
251
transformation of the readings was 2.27 + 0.03 in 20 assays, and 
the coefficient of variation was 6.3%. The consistency in the value 
of the slope can be a measure of accuracy as proposed by Cekan (1976)
Table A1
Assay of cortisiol in increasing volumes of plasma
Plasma Volume Cortisol Value 
(ml/tube) (ng)
0.6 3.8 + 0.1
n = 3 ....
.
O.k 2 .h + 0.2 
n = 3 "
o .2 1.U + 0.1
n = £ ...
0.7 + 0.1
° A
n = H
The amount of cortisol recovered decreased
at high plasma volumes.
252
Table A2
Recovery of cortisol in water in a single assay*
■d deviation.
253
Table A3
Recovery of cortisol in a&aeaug solutions in 20 
duglicate assays
Cortisol solution Cortisol concentration Coefficient
treated determined of(mean _+ standard error) variation
„ _____________________ -  - -
5ng/ml 5.7 + 0.2 
15
n = 2°
10ng/ml 10.0 + 0.2
8
- n = 20
n = number of duplicate assays.
- Solutions containing cortisol, 5ng/ml and 10ng/ml of water 
were run in duplicates along with the samples during the 
assays of cortisol. The recoveries obtained were a measure 
of accuracy of the assay method.
Table Ak
Duplication of samples in the same assay. 
Within-assay variation is calculated from duplicate 
values of plasma cortisol in 12 different samples 
determined in the same assay
Duplicate 
values of d d2
cortisol 
ng/ml
Samples 1 h.2 13.5 1 8 2 .2
3.7
2 7.2 1.3
t 7.3 ■ - ...  ^ r ^ "
3 9.7 10.2 10U
8.8
18.5 0
1 8 .5 4i»~
5 8 25 625
10
6 ■ 11 1 8 .2 331.2
13....._  _
7 29.2
3 .8 2.7 7.3
* 3.7
9 3.6 1 6 . 1 259.2
3.1
10 1.8 38. k 11»7 U.6
1.3
11 2.9 20.8 U3 2 .6
2.h
12 3.9 12.8 1 6 3 .8
— k.k
a2 = 3 6 1 1 . 0  
* ;12.3
for d and CV, see footnote on page 255*
255
Table A5
Duplication in two different assays** 
Inter-assay variation: plasma cortisol was 
determined in the same plasma samples in two
different assays
A* B* d
d2
1 6.8 6.1 11.2
,25 < ? ^
2 3.9 U.8 23.1 522.6
3 b.O 3.6 11.1 123.2
1* U.5 5.5 22.2 U92.8
5 U.5 U.8 '6.6 U3.5
6 h.i 6.1* k2.f2^ 1780
7 . 13.8 1U.3 3.6 13
8 12.5 1U.2 13.6 185
9 1.6 5.8 31 961
10 __1_3._5_ _v_&_._o_ __ , 12.5 156.2
f d2 = 1*1*18.7
CV = 1U.9
d deviation, calculated as in the text
C V inter-assay coefficient of variation 
calculated as in the text.
% = set of plasma samples.
*# s test of repeatability of assay.
256
Table A6
Test of Accuracy of Assay
A B C D
07 (2) (3) 0) (2) (3) (3)
0.2ml Amount Amount (D Amount Amount 
% Amountplasma of cor­ reco­ reco­ of cor­ Amount
%
' reco­ of cor -reco­
%
cortisol tisol vered tisol reco­ tisol vered reco­
concent­ added (pg) vered added vered vered added veredration (pg)(pg) (pg) (ps)
(pg) (pg)
h06 1000 1003 100.3 2000 2209 110.If 1*000 3778 9l*.l*
320 1000 1093 109.3 2000 2 2 1 6 110.8 1*000 1*017 100.U
385 1000 • 1079 107.9 2000 21 **9 107-̂ 1*000 3932 98.3
32k 1000 10H8 10i*.8 2000 2*»31 121.5 1*000 3855 96.3
391 1000 999 99.9 20Ĉ K 2012 100.1 1*000 3803 95.0
Mean Mean Mean Meat-n 5 Mean Mean
10l*l* 1Ql* 2203 110.0 3677. 96.9
To 0.2ml plasma containing low cortisol/lienv elfour sets of tubes (A-D) 
were added increasing amounts of cortisol 0 ng 1 ng, 2 ng and 1* ng per 
tube per set• these were extracted and assayed; assay values were 
corrected for recovery and mean value of set A subtracted from 
sets B to D to obtain recovered value (column(2). Within assay 
coefficient of variation was 11.1$.
257
Table A7
World Health Organisation (WHO) quality control of 
ygfH nimmunoassay
Mean of results Value obtained 
Date of all labora­ by the present 
tories (ug/100ml) method (ug/100ml)
13/6/77 9.0 8.6 +0.5 SE
... ..... . r ________________
27/6/77 n.2 1 8 .6 +0.1+
11/7/77 10.6 +0.1+
25/7/77 10.1+ 7.7 +0.5
8/8/77 a  ,6.8 ^ 16.30 +0.7
-----2-2-/8/77
V ,3.6 13.1 +0
---— «
Cortisol was assayed in plasma samples distributed by 
WHO to different laboratories including the laboratory 
where the present investigation has taken place.
258
Table A8
Standard curve of cortisol radioimmunoassay
Amount of steroid % bound* radioactive 
ng cortisol S E n
5 . 20ov..7..T ...... 0 . 6 20
2.5 ___________ 0.8 2030 7
1 1.2 20
0.5 1.6 20
0.25 • 80.3 1.3 2 0
SE = standard error.
n = number of observations considered.
* = the 100^ binding of radioactive cortisol is that
■which occurs, at zero concentration of the • 
non-rddioactive hormone.
(Antiserum was used at a total binding
between 25 and 375).
•
GO
-r f
259
Table A9
SUMMARY OF MONTHLY WEATHER OBSERVATIONS FOR THE UNIVERSITY OF IBADAN CAMPUS 
~ FROM DECEMBER 1975 THROUGH DECEMBER 1976
DEC. TA„ 
1975 J" FEB MAR APR MAY JUNE JULY Q"-AUG SEPT OCT NOV DEC
YEAR
1976
Mean Daily Minimum oc 17.a 18.3 21.7 22.2 21.7 21.1 21.1 20.0 20.0 20.0 21.1 21.1 20.5 20.7
Temp.
°F 6k 65 71 72 71 70 70 \ 68____ 68 68 70 70 69 69.3Mean Daily Minimum 
Temp. °C 32.2 * 32.8 33.9 33.9 32.2 31.1 .
v
2 9 U 2 7 . 8  2 7 . 2 29.1* 29.1+ 31.1 32.8 30.9
°F 90 91 93 93 90 88 C § 5 ______82_____ 81
Average Daily Mean 28.0 23.6 85
88 91 87.7
 °C 25 25.5 2 7 .8 26.9 26.1 ^ 25.3Temp. 23.9 21+.7
25.2 2 6 . 1 2 6 .7
°F 77 78 82 82
Extreme Max.Temp. 80.5 79 7 7 . 5
66.0
35.0 36.1 36.1+ 36.1 71+ 7 6 .5 77 79
80
°C 32.2 2 9. h 30.0 3 2 . 2 31.1 33.3 ' 3V.I+" 33.3
°F 93 95 97 98 97 c r 392 90 85 86 90 88 92 92.0Extreme Minimum 91* 10 17.8 - w 18.3 -7.2 17.T- 19.7+­
Temperature °C 17.8"" 1 6 .9 1 8 . 3 1 6 . 7 13.9 17.1
°F 53 50 6U 61+ £ 66
Total 65 63
61+ 65 67 62 57 62.7
Preci• pi• t* at« i• on mm 10.7 19.3 1+3.1+ 129.8 129.8 196.9 6 7 .6 25.7 39.1* 195.3 29-5 0.5 877.2 
inches 0.L 11 0.8 5.1 1+.8 7.7 2 . 7 1.0 1.5 7.7 1.7 0.0Mean Relative Humidity 
{%) at .7.00 h 9k 92 92 ... 9kMean Relative Humidity 95 95 9k 9l* 91* 95 91* 90 93.5
{%) at 16 .0 0 h 1*6 37 1+8 50 58 66
Lowest Relative 70 75 I k 61+ 69 57 1+1+ 59
Humidity 
(%) for Month 25 15 35 30 30 55 59 63 62 50 57 33 22 1+2.6
Total Sunshine (.hours)237.1 235.6 18 6 .9 1 7 8 .0 186.7 1 9 5 .0 16 0.1+ 95.0 59.0 113.3 127.9 197.6 218.9
260
Table A10
Mean haemoglobin concentration and packed cell 
volume during cool wet and dry hot seasons
Wet Season Dry Season 
___________Breeds________ Breeds
Item Brown Holstein Fulani All Brown Holstein Fulani All
Hb g/100 ml
Mean 8.8 8.8 10.9 9,5 8.8 $ 8.8 11.6 9.6
S D 1.0 0.7 0.8 1.3 .4.0" 0.6 1.0 1.6 
n 20 21 20 61 20 22 17 59
PCV (%)
Mean 26.3 25.2 2 6 .8 2 6 .8
S D 31 33.3 2.5 2.5 3.8 2.0
28.7
n 20 221 I4.0 U.li20 22 17 59
------
Haemoglobin concentration (Hb g/100ml) and packed cell volume 
(PCV %) were determined in the Brown , Holstein and 
Fulani heifers with the conventional methods,
S D = stand<a2rd deviation
n = number of observations
Wet Season = April - October
Dry Season = November to mid-March. , -
ox ^
261
Table AH
PCV {%) and Hb (g/100ml): cool wet and dry hot 
seasons compared
Breeds
Hb (g/100ml) Brown Holstein Fulani ALL heifers
Degree of Freedom 38 in 35 1 1 8
t 0.05 „ 0.5
’•5 v<
P P> 0.05 P> 0.05 P< 0.01 P> 0.05 
NS NS s NS
Packed Cell Volume
DF 3? 1+1 35 117
t 0.5 2.2 1.2 1.7
P> 0.05 Pi 0.05 P> 0.05 P> 0.05 
NS S NS NS
' J *
NS Not significant 
S Significant 
DF Degree of freedom 
t Student t value 
P Level of significance
Hb
PCV Packed cell volume.

263
Table A13
Analysis of variance of respiratory rates in heifers 
of three breeds of cattle during four periods of the year
Sources of Degree of Mean F*. Ratio Significance
Variation Freedom Square C D
Season 3 1+575.9 3.T > 0 .0 1*
| * - ... t v
Breed 2 1+163.8 0.0 3*
Time of Day 1 9731+.3 v7 . 9 0.006*
Season x ' Breed 6 1201.2 0 .9 8 0 .9 9
..  ^
Season x Time 3 11+1 8.8 ’ 0 .9 8 0 .3 3
Breed x Time 2 11+66.5 1 . 1 5 0 .3 1
Season x Breed x 
Time 1076.2 1 . 1 9 0 .9 9
t Residual \ 1 2 1229.3 0 .8 7
Total 95 11+85.8
Table A 14
Contribution^o total variation that occurred in the respiratory
rates
Season 9.6%
Breed 5.8% Total 22.5%
Time of the Day 6.8%
// = as determined by the ahctlysis of variance
* = significant.
264
Table A15
Mean rectal temperatures (°F) of individual Brown, Holstein 
and Fulani heifers at 07.00 and 15.00 hoars during 1+2 
consecutive days at different periods of the year as 
indicated in the table
DECEMBER-JANUARY MARCH - APRIL JULY - AUGUST OCTOBER--NOVEMBER
TIME OF THE DAI (HOURS)
0 7.0 0 1 5 .0 , 0 7 .0 0 15.0C 0 7.0 0 15 .0 0 0 7.0 0 15 .0 0
HEIFER No.
Brown 81+ 1 0 1.1+ 102.3 101.3 102.3 1 0 2 . 1 101.3 1 0 2 . 3
i? 86 1 0 1 . 1 102.3 101.3 1 0 2. U 101.3 1 0 2.4- 101.3 1 0 2 .3
f» 87 v 1 0 1 . 2 1 0 2 . 2 1 0 1 . 2 102.3 1 0 1.1+ 102.3 1 0 1.1+ 1 0 2.If
t! 89 101.3 1 0 2 . 2 102.3 101.3 1 0 2 . 2 101.3 1 0 2 . 3
?! 10191 101.3 102.3 102.3 101.3 1 0 2. Q 1 0 1 . 2 1 0 2.1+
Holstein 137 101.3 1 0 2. ^ Q t , 1 0 2. k 101.3 1 0 2.1+ 101.3 1 0 2 .3
! 1U5 1 0 1 . 2 1 0 2^ 1 0 2 . 2 102.5 1 0 1.!+ 102.3 101.3 102.5
If 11+8 1 0 1 . 2 1 0 2 . 2  101.3 102.3 1 0 1 . 3  1 0 2 . 2  101.3 1 0 2 .3
tl 151 1 0t>« 102.5 1 0 1 . 2 102.5 1 0 1 . 2 1 0 2.j 1 0 1 . 2 10 2 .6
t! 15̂ 1 0 1 . 2 1 0 2 .6 101.3 1 0 2. 1+ 101.3 1 0 2.1+ 1 0 1 . 2 1 0 2 .6
Fulani 20 1 0 1 . 1 101.9 1 0 1 . 2 1 0 2 . 2 1 0 1 . 2 1 0 2 .0 1 0 1 . 1 1 0 1 .8
tf 21 1 0 1 . 2 107.1 1 0 1 . 1 101.9 1 0 1 . 2 1 0 1 . 8 1 0 1 . 2 1 0 2 .3
!? 22 1 0 1 . 2 102.3 1 0 1 . 1 102 1 0 1 . 1 1 0 1 . 9 1 0 1 . 2 1 0 2 . 1
! 23 1 0 1 . 2 1 0 2 . 1 1 0 1 . 2 102.3 101.3 1 0 2 . 2 1 0 1 . 2 102.3
! 681 1 0 1 . 2 102.3 1 0 1 . 2 1 0 2 .0 1 0 1 . 2 1 0 2 . 2 1 0 1 . 2 1 0 2 . 2
265
Table A 16
Analysis of variance of rectal temperatures in 
heifers of three breeds of cattle during four 
different periods of the year
S V D.F. Mean F-Square ratio Significance L.S.D.
Season 3 0.05 6.77 0.001 0.12
Breed 2 0 .5I+ 78 .6 0 0 .0 0 1 0.13
Time 1 29.11 U3 *0U 0 .0 0 1 0.17
..............  _.....
Season x Breed 6 0.03 U.32
< ^ 0 0 1 ......
Season x Time 3 0.05 7 .8 2 0 .0 0 1
Breed x Time 2 0 .0 1 1.15 0 .3 2
Season x Breed x Time 6 0 .0 1 1.05 0 .1+0
Residual 72 0 .0 1
Total 95
< c
Table A17
Contribution* to total variations that occurred in
rectal temperatures
Season o.ook%
Breed 3.6155
Time of the day
(morning and
afternoon) 9b.09%
Total 91+%
SV = source of variation.
DF = degree of freedom; L.S.D. = Least significant difference, 
*  s determined by the analysis of variance.
266
Table A18
Analysis of variance o£ shade seeking scores in heifers 
of Brown ar 1 Holstein cattle grazed in the sun
Sources of Degree of Mean
Variation Variation Square F—ratio Significance
Breed 1 1 .U8 1 1 0 . 1 1 ,-T^. S
Season 3 0.19 1U.88 S
Breed x Seasoni 3 0 .0 1 NS
1 $
Residual 2k
Total 31
. ^  S = significant
NS = Not significant.
The ‘Holstein and the Brown Heifers were considered: the Fulani did not 
seek shade.
C f
Table A19
Mean percentage scores 6f shade seeking in the heifers 
curing different periods of the year: 
observations were taken on 10 randomly chosen days of 
each quarter
Brown Holstein Fulani
July - August 1976 1 9 .0 1+3.65 0
November 1976 33.9 9 1 . 2 0
December 1976 37.15 8 9 .1 2 0
March - April 1977 75.85 95.1+9 0
267
Table A20
Average scores of estrous intensity in heifers
Heifer■ No. JAN FEB MR AP MY JN JL AU SEP OCT NOV DEC
Brown 8h +++ +++ +++ ++4- +4-+ • + + 4-4*4- 4-4-4- ++ +++ +++
ft 86 +++ ++ +++ +++ 4-4-+ 4-4*4- 4-4-4- 4-4-4- 4-4-4- +++ +++ +++
If 87 +++ + +++ +++ +++ 4-4-4- 4-4-4- 4-4-4- +4-4- +4*+ +++ +++
If 89 +++ +++ +++ +++ 4-4*4* 4-4-4- 4-4-4- +++ +++ +++ +++< 5 2 T
If 91 +++ +++ +++ +++ 4-4*4* 4-4-4* +++ 4-++ +++ ++-:-
F
Holstein 137 +++ + +++ +++ ++ ++ 4v-4-4- 4-4*4- ++ 4-++ +++ +++
I I 195 +++ ++ +++ +++ 4-4-4* 4-4-4- 4-4-4- +++ +++ +++ +++
I I ++ ++ +++ +++ 4-4-4- 4-4-4- +++ 4-4-+ +++ +++
I I 151 +++ +++ +++ 4-4*4- ++ 4-4-4- 4-4-4- ++ +++ +++ +++
If -15̂ ++ ++ ++ ++ 4-4-4- 4-4-4- 4-4*4- 4-4-4- +++ +++ +++ +++
Fulani 20 ++ + «■ ++ ++ +++ + ++ ++ ++ + 4
I I 21 ++ ++ $ ++ +++ +++ ++ +++ ++ +++ ++ ++ +++
It 22 +++ + ++ ++ ++ + ++ ++ ++ +++ ++
It 23 +++ +++ +++ ++ +++ +++ ++ +++ +++ +++ +++ +++
ft 681 +++ ++ ++ ++ + ++ +++ ++ + ++ ++ +
Average estimate of the intensity of estrus determined as in the 
text in heifers through the year; (+++) high (++) medium and, (+) 
low intensities.
CJOr
268
Table A21
Distribution of the time of commencement of estrus 
through the 2^-hour day in heifers 
observations were made over one calendar year
Brown Holstein Fulani
Time of the 
day (Hour) n n A
5 - 7 18 - 10 . iOY^13
16 19
9-11 10 9
11 - 13 5 3
13-15 • ....’.<> r  3 k
15 - 17 5 k
A
• 17 - 19 O s 1 6
A
19 - 21 V 2 2 1
21 - 23 2 2 k
23 - 01 1 1 2
01 - - - 2
■-- ■ 1 '
03 - 05 9 6 8
n ' number of observations.
1
VO
Table A22
Sources of Degree of Mean
Variation Freedom Square F-ratio Significance
Month 11 1.5 1.U5 NS
J p  . . . .
Breed 2 0.03 0.03 NS
... ' ...V /
Time 3 2 1 . 1 2 20\ £ v 0.0 0 1**
Analysis of variance oft ine of onset of estrus in heifers 
through the year. Highly significant (**) effect of time of the 
day; and non-significant (NS) effects of month and breed.
270
Table A 33
Duration of estrous oeriod in
Holstein (K).$ Fulani > (F) heifers ' through the year.
197 3
JAN FEB !MAR APR | M Y JUNE JULY !AUG SEPT OCT MOV DEC
Heifer No 
B 184 22 12 15 24 18 31 17 23 31 30 .1 25
B 37 17 | 17 12 13 14 14 25 11 31 24 1 l7
B 88 15 10 15 12 15 - - i  -iH j. 15 ,. 18 14 12 pn | 13
B 89 16 10 3 22 12 12 25 10 14 14 13
B 91 17 17 19 17 21 . 13 14 13 16
13 IS u  V 9
B 92 * i
/
13 35 13 12
e 137 (16 10 12 30 15 13 / 28 13 13 13
(13 1 13 P
H 145 16 j 18 26 12 14 13 12 24 29 21
H 118 <14 3 1 10 ii 16 12 30 12 14 j
< $ 23 ji
H 151 - j (11 13 y 10 29 14 13 12
! ( 14 14
H 154 12 27 12 14 13
r 14 15 !
F 20 cii 10 & 12 23 22 30 27 27 12 ii Ij Ip
<12 \ s 23 29
F 21 15 C7 . 12 11 10 17 27 9 14 13 13
F 22 15 8 1 21 9 9 27 10 9 14 14 24
F 23 (22 14 17 n 10 9 12 22 12 15 14 
19 14 10 9 10 14 H j. a
F 681 10 28 $ TO n j 11
F 682 -------- | 11 11 13
Duration of estrus was determined as period during which the heifer 
stayed to be mounted by the teaser bull as described, in the text.
*>
UNIVERSITY OF IBADAN LIBRARY
272
Table A 25
Mean plasma cortisol concentration in Individual heifers
(Observations made on alternate days)
Jan - Dec March - April July - Aug. November
SE n - SE n X SE n SE nX
X X
Brown 84 5.3 j+0.4 16 6.2+ 1.0 20 6.4 +0.7 20 5.7 + 0.3 23
tt 86 5.6 +0.6 18
»» 6.5JH 0.6 19 7.. 2 +0.7 20 5.7 + 0/6 1987 4.3 +0.5 17 5.1+ 0.6 20 6.4 +0.5 20 5,6 +i* 0.5 .2089 5.0 +0.5 16 6.3+ 0.5 18 7.5 +0.7 6.0 + 0.5 22
ft 91 4,4 +0.4 20 5.1+ 0.4 19 7.4 +0.6 19 6.2 + 0.8 21
Holstein 137 4.2 +0.4 15 5.7+ 0.6 19 5.4 +0.4 20 5.0 + 0.4* 22
If 145 4.5 +0.3 19 6.9+ 0.5 21 ^ 5 . 0 +0.4 19 5.1 + 0.4 21
ft 148 4.5 +0.3 16 7.0+ 0.4 19 7.4 +0.1 19 5.7 + 0.5 20
ft 151 5.2 +0.4 19 6.0+ 0.6 19 7.2 +0,6 18 5.7 + 0.5 19
ft 154 4.8 +0.6 18 6.1+ 0.6 IS 6.9 +0.8 21 7.6 + 1.2 20
”
Fulani 20 4.8 +0.4 17 5.7+0.5 20 5.2 +0.5 18 5.0 + 0.4 23
ft 21 5.5 +0.7 17 5•5+0.5 21 5,8 +0,5 20 5.2 + 0.5 11
ft 22 6.8 +0.7 19 5 *8+0•6 IS 6.9 +0.6 18 5.7 + 0.5 23
ft 23 *5.6 +0.5 19 5 •7+0.6 20 6.1 +0.6 19 4.8 + 0.4 20
tt 681 4.5 +0.5 24 5*6+0.4 21 6.8 +0.6 23 5.2 + 0.6 22
Mean (x) (with st:andard error (S E ) plasma cortisol concentration in
heifers on alternate days during different quarters of the year.
n * number of observations.
t
* 273
Table A 26
Mean plasna cortiaolconcentration in Individual heifers
J anu ary-De comber March - April • July - August October-November
X SE n X SE n X SE n X SE n
irown 84 5.70 +0.45 35 5.93 +0.61 40 5.78 +0.39 40 5.70 +0 • 34 23
11 86 4.91 +0 • 36 36 5.97 +0.45 38 6.14 +0.37 38 5.55 +0.54 24
ii 87 5.68 +0.42 36 6.45 +0.47 35 6.83 +0.46 40 5.30 +0.4 25
ii 89 4.92 +0 • 35 36 6.11 +0.42 38 7.26 +0.60 37 6.0 +0 • 48 22
ii 91 4.36 +0.38 20 5.12 +0.36 19 7.44 —+—0.57 32 6.19 +0.80 21
Holstein 137r 4.62 +0.27 31 5.72 +0.41 37 5.45 ^f.27 41 5.05 +0.41 22
t; 145 4.86 +0.28 29 6.82 +0.43 40 6.46 +0.33 39 5.06 +0.45 24
ii 148 4.93 +0.22 29 6.49 +0.2 38 7.4 +0.44 38 5.5 +0.4 27
ii 151 5.08 +0.32 30 6.30 +0.36 38 6.96 +0.45 36 5.69 +0.53 24
»t 154 4.81 +0.61 18 6.14 +0.63 18 6.9 +0.79 21 7.59 +1.18 20
Tulani 20 4.80 +0.42 32 5.58 +0.40 40 5.57 +0.41 36 4.96 +0 • 38 23
ii 21 5.35 +0.54 33 5.22 +0.41 40 6.31 +0.42 39 5.09 +0.39 26
ii 22 6.50 +0.53 35 6.07 +0.51 36 6.88 +0.49 33 5.72 +0.50 23
ii 23 5.34 +0.29 37 5.84 +0.46 40 6.60 +0.43 34 5.06 +0.38 25
ii 681 4.48 +0.48 5.61 +0.41 21 6.83 +0.56 23 5.22 +0.58 22
x = Mean
SE = Standard error
n = Number of observations.
Table A 27
Analysis of variance of plasma cortisol levels in heifers; levels 
at diestrus, estrus and the mean of values during four 
different quarters of the year v/ere compared
Sources of Degree of Mean Significance 
variation freedom square F-ratio level ‘ L.S.T).
Main effect 7 59.25 12.76 0.001**
Cycle day tri*j 171.24 36.39 0.001** 3.45
. -. ~ / 0 C  -..—  ...IT -
Season 3 21.74 0.004** 2.9S
Breed 2 3.53 o. 9 9
Day x season 6 5.8i? 1.2 0.23
A  N
Day x Breed 4 3.92 0.3 0 .9 9
■
Season x Breed 6C 5.49 1.18 0 .3 2
.
Bay x Season 
x Breed 12 3.73 0.80 0.9S
Residual IDS 4.64
Total 143 • 7.37
** = highly significant 
L.S.D. = least significant difference.
275
Table A 28a
Analysis of variance of plasma cortisol concentrations in Brown, 
Holstein and Fulani heifers through four different quarters of
the year
Sources of Degrees of Mean
variation freedom squares F-ratio P level
Breed 2 0 • 25 i3nt 6.37
Season 3 4,03 16,07 0.001**
Breed x Time 6 0.37 1.47 0.20
Residual 36 0 . 2 ! ^
Total' 47 I T
P = Significance level 
** = Highly significant
# ■ '  »
O '  Contribution* to total variation
Breed 2.2%
Season 50.4%
Total 52.8%
* » As determined by the analysis of variance.
276
Table A 29
Rectal temperature and respiratory responses of heifers in the sun
TIME OF THE DAY (HOUR)
07.00 11.00 15.00 18.00
HEIFER NO. RR RR Tre RR RR
Brown 84 100.2 30 101.8 40 102.4 52 102.2 50
«« 87 101.5 28 102 52 102.2 64 102 56
tt 92 101 32 102.4 54 102.2 60 101.9 64
ti 86 100.8 28 101.1 50 102 56 102.2 58
tt 91 101 26 102.4 42 102.4 60 102 58
*
Holstein 137 jl00.4 36 102 90 102.4 88 102.4 84
1 r 1 
tt 145 101.6 42 103.6 106 103.4 92 103.2 90
ft 148 101.2 30 1i  102 110 102.2 100 102 88
ft 151 100.3 40 102.6 90 102.5 100 102.6 82
* tt 154 101.5 36 104.5 84 104.5 00 106 84
Fulanl 20 100.6 22 101.2 28 102.2 44 101.4 32
»t 21 101 14 101.6 40 102.4 28 101.8 26
tt 22 101.2 : 16 101.7 36 102.8 40 102.3 28
tt 23 100 20 101.8 37 102.6 36 102 34
J
ft 681 101.2 18 102 1 26 102.4 34 101.5 36
Tre = Rectal Temperature (°F)
RR = Respiratory rate (breaths/minute)
Heifers were kept in the paddock throughout the day unshaded 
when the readings were taken.
277
Table A 30
Analysis of variance of respiratory rates of heifers
in the sun
s v B F
Mean
Square F-ratio Significance
Time 3 4069.75 71.57 0.001 S
Strain 2 / 9692.51 170.45 0.001 S
Time x Breed 6 359.85 0.001 S
Residual 48 56.86 ; #  ...
Total J 59 618.35 y - - —  —
______
r
Contribu tion* to total variations that occurred
Time . 33%
Breed 53%
Total - 86.6%
c T
S V . source of variation 
0F degree of freedom 
S significant effect
= as determined by analysis of variance.
UNIVERSITY OF IBADAN LIBRARY
UNIVERSITY OF IBADAN LIBRARY
UNIVERSITY OF IBADAN LIBRARY
281
Table A 34
Analysis of variance of respiratory rates of heifers kept 
in the shade and in the sun
Sourcesof Degree Mean F-ratio Significancevariation of freedom Square level
Main effects 6 8691.81 195.62 0.001**
Breed 2 16071.76 361.72 0.001**
Time of the day 3 5545.52 124.81 0,001**
Typ£ of treatment 1 3370.8 75.87 0,001**
- "
Breed x Time 6 579.21 13.04 o,poi**
Time x Type 2 627.78 14.29 0,001**
Breed x Time x Type 70.72 * 1.59 0.157
Residual 96 N 44.43
Total 119 525.09
^ 3 2 n"tribution* to total variations that occurred
Breed 52%
Time of the day 27%
Type of treatment 5%
Total 83.5%
** = Highly significant Effects
* = As determined by analysis of variance.
282
Table A 35
Analysis of variance of values of rectal temperature in 
heifers in the shade and in the sun
Sources of Degree of Mean F-ratio SignificanceVariation Freedom square level
Breed 2 3.47 8.10 0.001 s
.. -
Time of the day 3 13.54 31.62 -4 0.001 S
Type of Treatment 1 11.27 ......2...6......3...3.. 0.4)01 . s
2-way interaction 11 0.62 1.45 0.16 N S
Breed x  Time 6 0.54 1.37 0.2 N S
Breed x Type 2 0.2% 0.35 0.9 N S
Time x Type 3 1.0 2.35 0.07 N S
BreedxTimexType 6 0.35
0.82 0.9 N S
... c
Residual " A  ! 0.43
Total 0.91
Contribution* to total variations that occurred
Breed 7%
Time 3 7 %
Type of treatment 1 0 %
Total 54%
* = As determined by analysis of variance
S = Significant
N S  *= Not Significant
Observations in the shade were made in the pen.
UNIVERSITY OF IBADAN LIBRARY
284
Table A 37
Diurnal plasma cortisol concentration in heifers (ng/ml) Experiment 3)
Time(h) 7-8:00 11-12:00 15- 16:00 18- 19:00
5.0 W 8 4.8 4.7
87 (2) 5.2 0^10.0 5.1 3.2 
86 (6) lO.jK 2r 6.0 =7.8 5.9
89 6.2 6.0 2.4 3.5
Holstein 137 6.2 5.2
< > •  * • 3.5
145 3.4 7.2 3.0 3.5
148 5.5 6.6 3.4 4.1
151 6.9 7.1 6.6 5.1
154 19.0 7.2 3.5 3.0
Pulani 20 5.2 6.1 5.1 4.5
22 3.0 3.9 2.9 3.0
23 4.5 3.6 6.8 5.3
21 2.9 3.4 3.6 3.0
t*
Table A 38
Analysis of variance of diurnal plasma cortisol
concentration In heifers (Experiment 1)
Sources of Degree of Mean
variation freedom square F-ratio Significance
Time of day 2 7.26 lift* 0.3 N S
Breed 2 4.10 °-89 0.2 N S
Time x Breed 2 3.30 0.71 0.9 N S
Residual 27 0.97
Total 35 ^ 4 . 5
— -------
N S  * Not Significant
286
Table A 39
Correlation between plasma cortisol and rectal temperature
' df heifers kept in the sun (Experiment 1)
Breed r r2 Signi- Slope Intercept Standard error 
________1j|_ _f_i_c_a_n_c_e_ _ L__\ - .Jj of determinatl<
Brown 0.5 0.26 0.055 1.90 -187.64 2.6
Holstein 0.49 0.25 0.05 0.80 - 76.73 1.82
Fulanl -0.27 0.07 0.194 -0.62 68.07 1.55
o j r - * _ - • • , ' _•' 1 i
.
r = Correlation -coefficient.
287
Table A 40
Analjrals of variance of diurnal plasma cortisol concentrations
in heifers (Experiment
Sourcesof Degree of Mean
variation freedom square F-ratio Significance
...............
Time 3 15.10 0.05 S
Breed 2 17.14 0.05 S
' -■ -1 
Breed x Time 6 6.57 1.22 0.31 NS
r V *
Residual f 36
j s r ]
Total 47 6.64
Time of the day 14%
Breed 11%
Total 25%
* = As determined by analysis of variance
S * Low significance
NS * Not significant
UNIVERSITY OF IBADAN LIBRARY
289
Table A 42
Analysis of variance of circadian plasma cortisol
concentration (ng/al) In heifers (Experiment 4)
Sources of Degree of Mean
variation freedom square F-ratio Significance
Main effect 8 2.67 1.76 0.119 NS
Breed 2 0.69 0.999 NS
Time 6 3.33 0.062 NS
✓
Breed x Time 12 1 1.00
• 5?
Residual 42 1.S1
Total 62 ^ . 6 6
&
Contribution_*_ _t_o_ __t_o_t_a_l_ __v_a_r_i__a_t_i_o_n__ _t_h_a_t__ _o_ccurred
B.J c reed 1.4%
Time 19.36%
-
Total 20.7%
NS Not significant
* As determined by analysis of variance.
290
Table A 43
Mean rectal, temperatures of nonlactating pregnant 
cows and nonlactating nonpregnant nulliparouS heifers 
in the sun, unshaded and shaded
T I M E of the day (Hour)
07-08.00 1 14-15.00 14-15.00
% Unshaded Unshaded Shaded
Rectal Temperatures (°I
co w s BROWN x 101.38 102.68 b 101.50 
SD + .27 + .99 + .92 
n 5 \ 54 r :.
HOLSTEIN
x 101.3 104.94 103.2 
SD + 0.28 + 1.69 
: * r '..1 .<> r  «
5
HEIFERS BP.C’TO .
1 1 X  100.82 102.08 101.22 
. j SD + .57 + .52 + .39 
/■**>*** 5 5
1 HOLSTEIN x 100.72 103,68 101.72 
1 SD + .51 + 1,47 + .54 
i # . n 5 5 5
j v
j I-ULAN I x 100,66 101.96 101.08 
SD + .32 + .5 + 0.23 
n 5 5 5
fls number oP etniniols
UNIVERSITY OF IBADAN LIBRARY
292
Table A 45
Analysis of variance of plasma cortisol concentration 
In heifers Injected with saline and ACTH
Sources of Degree of Mean
variation freedom square F-ratio Significance
*
Time interval 8 1173.17 103.79 0.001**
Breed 2 458.21 40.54 0.001**
Type of treatment! 10976.61 < p971.17 0.001**
1
Time x Breed 16 45.29 4.00 0,001**
v N y
Time x Type 8 801.47 70.00 0.001**
Breed x Type 2 349.80 30.94 0.001**
TimexBreedxType 16 47.87 y 4.23 0.001**
Residual 54
Total 285.35
107 !
- ...
Contribution to totral variations that occurred
Type 36%
Time 30%
Breed 2%
Total 70%
** - Highly significant
293
Table A 46
Analysis of variance of plasma cortisol values In
heifers Injected with ACTK
” --’--- "" ■
Sourcesof Degree of Mean
variation freedom square F-ratio Significance
Main effects 9 1636.25 110.89 0,001**
Breed 2 764.32 0.001**
Time 7 1949.66 128.21 0.001**
Breed x Time 14 64.. 61V 4.25 0.001**
Residual v 
Total 349.91
** = Highly significant,
to
_______
294
Table A 47
Analysis of variance of plasma cortisol values in
heifers injected with saline