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Effect of heat stress on conception in a dairy herd model under South African conditions
EFFECT
OF HEAT
STRESS ON CO~CEPT~DN IN A DAIRY SOUTH AFRICAN CONDITIONS
HERD
HODEL
UNDER
J.H. du Preez,' S.J. Terblanche,2 W.H. Giesecke,' C. Maree3 and M.C. Welding4 IDepartmentof AgriculturalDevelopment,VeterinaryResearch Institute Private Bag X05, 0110 Dnderstepoort,Republicof South Africa Faculty of VeterinaryScience 2Departmentof Theriogenology, Universityof Pretoria,Private Bag X04, 0110 Onderstepoort Republicof South Africa 'Departmentof LivkstockScience,Faculty of Agriculture Universityof Pretoria,0002 Pretoria,Republicof South Africa 48iometricand DatametricServices Departmentof AgriculturalDevelopment Private Bag X640, Pretoria0001, Republicof South Africa Received
for
publication: Accepted:
October 30, 1ggo Febz=uary IO, 1991
ABSTRACT Three regressionmodels are proposed for predictingreproductionin a model dairy herd under South African conditions. Conception rate (CR%) was related to mean monthly temperature-humidity index (THI) by; CR% = to 31,15THf - 0.25TH12 - 890.2, and first service conceptionrate (FSCRX) THI by; FSCR# = 173.45 - 1.79THI. Conceptionrate was related to numerical month of the year (M) by; CR% = 11.86&l - 0.82M2 + 26.36. The relation between mean monthly THI values and the conceptionrate of dairy cattle is Further investigations to test the proposed regression significant. models under various dairy herd conditionsand to improve reproductionin South African dairy herds are needed.
Key words: conceptionrate, first service conception rate, heat stress, temperature-humidity index INTRODUCTION High sensible temperature and humidity are associated with seasonal declines in the reproductiveefficiencyof domestic cattle (I-2). From literature referred to by Du Preez et al. (31, Giesecke (4) and Hahn (5) it is apparent that thermal conditionsare a constrainton the performance of farm animals, particularlyin high-yieldingdairy cattle. The effects of thermal stress on reproductionmanifest themselvesin several physiologic mechanismsand include debilitating effects on conceptionrates, duration and expressionof estrus, etc. (6-9). At present, the temperstureAcknowledgments The authors thank Mrs. C.A. Smith for
typing of the manuscript, Mr. A. Kruger for data processing and the Department of Agricultural Development for financial support.
MAY 1991 VOL. 35 NO. 5
1039
THERIOGENOLOGY humidity index values are the most practical means of assessing the exposure of cattle to heat stress (IO). Warmmonths are more closely associated with lower conception rates than cool months (1). The average tempersture-humidity index of the second day before breeding is closely correlated with conception rate (2). The thermoneutral zone for cows is between 0” and 16°C (6). Cows experience heat stress when the temperature rises above 23.8’C at a relative A temperature-humidity index value of 70 or less is humidity of 80% (11). classified as normal; values above 70 are stressful to cattle (12). The Livestock Weather Safety Index (LWSI) indicates that in large areas of South Afxica and Namibia for prolonged periods of the year warm climatic conditions cause heat stress in food-producing animals, especially in dairy cattle, thereby hampering their performance (3, 13). The purpose of this study was to investigate the relation between temperature-humidity index values and conception rate in dairy cattle in Betha1 district, a highly populated dairy area of South Africa, and to determine an equation for the accurate prediction of the conception rate and first service conception rate of dairy cattle under various temperaturehumidity index conditions and et different periods of the year.
MATERIALSANDMETHODS Dairy Herd Model:
Experimental
Animals
The investigation was performed from 1987 to 1989 on a herd of 185 Friesian cattle on the Transvaal Highveld near Bethal (latitude 26’27’5, longitude 29’29’E and altitude 1663 m) in a semi-intensive system. The total number of lactations from 1987 to 1989 was 546, with an average per The herd was machine-milked three times a day. The cows cow of 2.9. varied in age, number of lactations and daily milk yield. Breeding occurThe standard of management, animal husbandry and red throughout the year. All artificial inseminations were dons by two hygiene were excellent. Milk production varied from 4’l’LY to 13165 kg per qualified inseminators. Estrus observation efficiency was good, and obserlactation of 300 days. vations were always performed by the same trained personnel. The calculated mean interval between estrus periods was 24. Cows were culled after the fifth unsuccesfull insemination. Meteorological
Data
Meteorological data were obtained from the South African Weather Bureau Publication WB 40 (14) as described by Du Preez et a1,(3). lhe temperature-humidity index values (Table 1) were calculated according to the methods described by Kibler (15). Reproduction
Parameters
The relationship of reproduction parameters conception rate and first rate to heat stress (temperature-humidity index service conception The reproductinn parameters values) were investigated on a monthly basis. for a five-month period (November until March) with a high (> 7(J) tempeexperienced heat stress, rature-humiaity inoex, during which dairy cattle were compared with a five-month period (May until September) with a low experienced either (< 70) temperature-humidity index, during which cattle no stress or minimal heat stress.
1040
MAY 1991 VOL. 35 NO. 5
4
ul
!! ?
F
Fj
72.9
7O.S
71.9
1908
1909
Mean
69.6s
70.1
71.2
70.5
7Q.3
Mar
67-6
72.0
73.9
Feb
index
63.9
63.4
63.5
64.9
57.7
58,5
5tL3s
56.4
The mean THX values sw
67.0
64.9
66.5
69.5
May
Jun
(THI) values
Months by THI values
temperature-humidity
for that month of that year,
72.2
1987
aNot available
Jan
1989
The mean monthly
‘/ears
Teble 1.
62.4
64.7
62.1
40.5
Au9
1920 to 1984
64.2
65.7
63.4
63.5
Sap
(3$14)
67.2
C&4
68.4
64.8
Ott
69.6
69.6s
69.6s
69.7
NW
to the dairy herd modsl at Betha
for the period
57.8
58.0
58.0
57.3
Jul
applicable
71.3
71.08
71.0s
71.8
Dee
For 1987 to
THERIOGENOLOGY Classificationof Temperature-humidity Index Values The temperature-humidity inaex values were classifiedaccordingto the LWSI of the Livestock Conservation Institute (12) to evaluate whether dairy cattle were heat stressed:Temperature-humidity index of 70 or less indicatednormal LWSI level, 70 to 78 indicatedan alert level, 79 to 83 indicateddanger level and 83 or above indicatedan emergencylevel. StatisticalMethods A polynomial of a suitable degree was fitted to the data (1987 to 1989, Table 2) by means of a polynomialregression(16). Three regression models were fitted to the data. The first regressionmodel was used to predict conception rate percentage (CR%) according to the mean monthly temperature-h~idityindex values. The second regressionmodel was used to predict the conceptionrate percentageby numericalmonth of the year; and the third regressionmodel was used to predict the first service conception rate percentage (FSCff%) according to the mean monthly temperature-humidity index values. Predictionof ConceptionRates The monthly and five-monthlymean conceptionrates for dairy cattle according to the equation: CR% = 38b.3 - 4.62THI (Z), and the three regression models as describedunder statisticalmethods were investigated and used to predictconceptionrates and first service conceptionrates. RESULTS PolynomialRegressionModels The second order polyn~ial regressionof the monthly true CR on the mean monthly THI data (Figure 1) gave: CR% = 31.15THI - 0.25TH12 890.2. This model explains73X of the variationin CR fR2 = 0.726). The second order polynomialregressionof the monthly true CR on the numerical month of the year (Figure 2) gave: CR% = 26.36 + 11.86M - O.8ZM2. This model explains 74% of the variationin CR (R2 0.737). The second order polynomialregressionof the monthly true FSCR on the mean monthly THI data (Figure 3) gave: FSCRX = 173.45 - 1.79THI. This model explains 58% of the variationin FSCR (R2 = 0.576). q
DISCUSSIUN The mean actual monthly conceptionrate and first service conception rate were at their lowest (36.4% and 32.8%) in January, while the mean monthly temperature-humidity index value was at its highest (71.9). The first service conceptionrate was at its highest (73.5%)in June while the monthly t~perature-humidityindex value was at its lowest. There was a decrease of conception rate with increasing temperature-humidity index The data applicableto the dairy herd model (Table 2) values (Table 2). indicate distinct trends,due mainly to an inverse nonlinearrelationship between the temperature-humidity index and conception rate (Figure I), temperature-humidity index and numericalmonth of the year (Figure 2) and temperature-humidityindex and first service conception rate values (Figure 3). Ingraham et al. (17) showed that the conceptionrate of 191 cows serviced on days with an average temperature-humidity index below 66 was 67% compared with 21% for cows serviced on days with an average temperature-humidity Index above 76. 1042
MAY 1991 VOL. 35 NO. 5
5 tn
kl
g
f
37.4
44.3
PFSCR (%)d
45.7
46.0
44.1
SE.4
46.9
46.8
47.6
54.6
49.3
63.5
56.7
55.0
70.1
Mar
regression
54.6
60.7
62.7
Ml.5
40.7
60.8
67.0
Apr
Months by values
different
(P)
index
(THI)
57.8
57.7
73.5
68.1 69.8
61.0
65.2
120.8
69.4
69.4
65.6
119.9
65.0
60.0
Jul
70.0
actual
conception
62.5
69.0
68.6
101.8
70.0
83.0
62.4
Aug
as FSCRI applicable
Jun
65.2
68.2
98.2
59.4
67.0
63.9
May
CR% as well
equations
of
and corresponding
model
values
rate
56.2
53.2
60.6 63.3
64.7
77.8
62.2
54.5
67.2
act
dairy
(CR%), the
66.9
85.7
52.1
64.2
64.2
Sep
to
to the equation: CR% q 388.3 - 4.62THI (2). to the regression equation model: CR% = 31.15THI - 0.25THI2 - b50.2. to the regression equation model: CR% : 26.36 + 11.86M - 0.822. M = month of the year in numerical to the regression equation model: FSCR% = 173.45 - 1.79THI. true CR and FSCR are 59.2 and 55.3%. 50.7% for the hot months frjov to Mar) and 68.4% for the cool months (May to Sepf. FSCR% was 48.6% for the hot months (Nov to Mar) and 62.2% for the cool months (May to Sep).
40.9
PCR (%,)b
PCR (%)=
a&cording bAccording “According dkcording The overall The CR was The actual
32.8
54.7
FSCR (7;)
PCR (%)a
71.9
36.4
71.2
by means of
Feb
1989
and predicted
temperature-humidity
CR% (FSCffi)
Jan
to
service
THI
1987
first
The mean monthly
CR (%)
data
monthly
Mean
Table 2.
Nov
model
order.
49.0
58.0
52.7
67.2
50.0
57.4
69.6
herd
mean monthly
true
46.5
51 .o
46.6
60.7
53.8
55.2
71.3
Dee
for
Figure
I
I
I
I I
I I I
>- - .k_?
I
I
I
----Y_ -. -. \.
\
‘_---
\
I
‘_-----.
.
I
.
.
\
\
-.--\
I
\
\
I
‘-
I
A’\ \ \. \ \\
‘\ \
\
The actual according CR --, actual
CR ---
and
rates values. predicted
and predicted conception to the mean monthly THI
:
Ingraham’s
= 31.15THI Legend CR --.
(CR%
(14)
0.25TH12
890.2) predicted
-
56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 Temper&we-humidity index
-
1.
30
40
50
60
70
80
90
Figure
2.
0
20
40
60
80
100
actual
Feb predicted
the numerical CR --.
and month
conception of
the
rates
Legend
= 26.36
:
Ott
Actual
c 11.86M
Ang Sep (CR%
year.
Jul
MOIlth
Mar Apr May Jun
according to and predicted
The
Jan
0.82N2) CR ---
-
,.
Nov Dee
” *E_*--,-
”
THERIOGENOLOGY
1045
MAY 1991 VOL. 35 NO. 5
THERIOGENOLOGY Temperature-humidity index values grouped accordingto the categories of the Livestock Wheather Savety Index (12) and the Livestock Wheather Savety Index for lactatingdairy cattle (6,7) suggest that within the nor-ma1 range of temperature-humidity index values of up to 70, dairy cattle show optimal performance,experience no significantheat stress and are not aaversely affected by handling (101. Johnson (IS) showed that the critical temperature-humidity index value for milk productionis 72. The temperature-humidity index threshold for reproouctionseems to be in the region of 65 for conceptionrate and 62 for first service conceptionrate (Figures1 and 3). It is apparentthat heat stress affects the conception rate and first service conceptionrate long before the temperature-humidity index rate reaches 72, when milk yields start to drop significantly. The predicted conception rates according to the mean monthly temperature-humidityindex and numerical month of the year compare favorablywith the actual mean monthly conceptionrates (Table 2). Ulberg and Burfening (19) showed that a I'C increase in rectal temperaturein COWS within 12 h after inseminationreduced the pregnancyrate from 61 to 45%. Warm months were more closely associatedwith lower conceptionrates than with cool months; month effects appeared to be accountedfor by the climatologicalmeasurements (20). Wolfenson et al. (21) showed that conceptionrate was higher in cooled than in noncooledcows (59 vs. 17X). Fertilizationis normal in heat stressedcattle (8) so embryonicdeath is responsiblefor decreasingconception rate of cattle in hot climates ($9). Nonty and Racowsky (22) suggest that the reduced fertilityof summer heat-stresseddairy cows may result from decreased viabilityand developmentalcapacityof Cay-6 to Gay-8 embryos. The mechanismsunderlying these observedadverse effects of heat stress survivabilityof embryos are unknown, but they may be due to a direct action of heat on the embryo or to an indirect effect that is mediated by the uterine environment. Heat stress between Days 8 to 17 of pregnancy altered the uterine environment as well as growth and secretory activity of the conceptus. Conceptuses were lighter, and the uterine environmentwas either unable to support embryo developmentor was toxic to the embryo (19). The new regressionmodel (CR% = 3?.15THI- 0.25THIz- Cr90.2) provided fairly accurate predictionsof conceptionrate (Table 2, Figure I> and is recommendedfor South African conditionsinstead of the formulacalculated by Ingraham (17). Predictingconceptionrate according to the month of the year is not recommended,because it can be used only under similar climatologicalconditionsand is insensitiveto changes in actual temperature-humidityindex values. The new regressionmodel (FSCRX = 173.45 1.79THI) to calculate the first service conceptionrate if the temperature-humidityindex values are known can also be used to great advantage under Southern African conditions. Precautionsagainst heat stress such as shade, air movement,cooled drinking water, diet alterations,wetting and the like (13) can possibly improve conceptionrate and first service conceptionrate in the Bethal district of South Africa. The calculated formulaeto predict conceptionrates under SouthernAfrican conditionscan be used to implementshort, medium and long term precautionsagainst heat stress in dairy cattle with low conceptionrates. In conclusion,preventative animal husbandry and management precautionsagainst heat stress, which may increaseconceptionrate and first service conceptionrate, can be taken in areas in South Africa, where reduced conception rates and first service conception rates are predicted with the regressionmodels Further according to the te~erature-huinidity index values, investigationsof the effect of heat stress on reproduction of dairy cattle in South Africa are suggested. MAY 1991 VOL. 35 NO. 5
1047
THERIOGENOLOGY REFERENCES 1.
Gwazdauskas,F.C., Thatcher,W.W. and Wilcox, C.J. Physical,environmental, and hormonalfactorsat inseminationwhich may effect conception. J. Dairy Sci. -56: 873-077 (1973).
2.
Ingraham,R.H. Discussionof the influenceof environmentalfactors on reproductionof livestock. &: LivestockEnvironment,Proceedings of the InternationalLivestockEnvironmentSymposium,SF-01-74, AmericanSocietyof AgriculturalEngineers,St Joseph,Michigan,1974, p. 55.
3.
Du Preez, J.H., Giesecke,W.H. and Hsttingh,P.J. Heat stress in dairy cattle and other livestockunder SouthernAfrican conditions: 1. temperature-h~idityindex mean values during the four main seasons. OnderstepoortJ. Vet. Res. 57: 77-87 (1990).
4.
Giesecke,W.H. The effect of stress on udder health of dairy cows. DnderstepoortJ. Vet. Res. -52: 175-193 (1985).
5.
Hahn, G.L. Menagementand housingof farm animals in hot environStress Physiologyin Livestock,Vol. '2, ments. &: Yousef,M.K.,(ed) Ungulates.CRC Press Inc., Boca Raton, Florida,1985, pp. 151-174.
6.
Bianca, W. Animal responseto meteorologicalstress as a function 4: 119-1315 (1970). of age. Biometerology
7.
Cavestany,D., El-Wishy,A-B, and Foote, R.H. Effect of season and high enviro~ental temperatureon fertilityof Holsteincattle. J. Dairy Sci. 8: 1471-1478(1985).
0.
Drost. M., Thatcher,W.W. Heat stress in dairy cows. Veterinary Clinics of North America:Food Ani. Prac. 3: 609-618 (1987).
9.
Fuquay, T.W. Heat stress as it affects animal production. J. of Ani. Sci. -52: 164-174 (1981).
10.
Yousef,M.K. Stressphysiology: definitionand terminology. In: Yousef, M.K., (ed) Stress Physiologyin Livestock,Vol. 1, BasiF Principles,CRC Press, Inc., Boca Raton, Florida,1985, pp. 3-7.
11.
Nickerson,S.C. Mastitismanagementunder hot, humid conditions.&: Proceedingsof the Dairy Hsrd ManagementConference,Macon GA, 1987, pp. 32-38.
12
Anonymous. InformationRelease. Patternsof TransitLosses. Livestock ConservationInc., Omaha, NE, 1970.
13
Du Preez, J.H. and Giesecke,W.H. Die uitwerkingvan hittestresby melkbeeste. South African Vet. Med. 3: 28-35 (1990).
14.
Weather Bureau Departmentof EnvironmentalAffairs. Climate of South Africa, ClimateStatisticsup to 1984, WB 40. GovernmentPrinter, Pretoria (1988).
1048
MAY 1991 VOL. 35 NO. 5
Environmental physiology and shelter enigeneering. 15. Kibler, H.H. Thermal effects of various temperature-humioity combinations LXVII. of Holstein cattle as measured by eight physiologicsl responses. In: Research 8ulletin Missouri Agriculatural Experiment Station, 564, p. 862. 16. Draper, N. and Smith, H. Applied regression Wiley & Sons, New York, 1981, pp. 266-273. 17.
snalysis.
2nd ed.,
John
Ingraham, R.H., Gillette, D.0. and Wagner, W.D. Relationship of temperature and humidity to conception rate of Holstein cows in subtropical climate. J. Dairy Sci. 7: 476-481 (1974).
18. Johnson, H.D. Physiological responses and productivity of cattle. Yousef, M.K., (ed) Stress physiology in livestock, Vol. 1, Basic ciplea, CRC Press, Inc., Coca Raton, Florida, 19b5, pp. 4-19.
In: Prs-
19. Ulberg, L.C. and Burfening, P.J. Embryo death resulting from adverse environment on spermatozoa or ova. J. Ani. Sci, -26: 571-577 (1967). 20. Gwazdauskas, F.C., Wilcox, C.J. and Thatcher, W.W. Environmental managemental factors affecting conception rate in subtropical J. CIairy Sci. -58: 88-92 (1975). climate.
and
21. Wolfenson, D., Fla~nbaum, I, and Berman, A. Hyperthermia and body energy store effects on eetrus behaviour , conception rate, and corpusluteum function in dairy cows. J. Dairy Sci. 2: 3497-3504 (1988). 22. Monty, D.E. and Racowsky, C. In vitro evaluation viability and development in summer heat-stressed, dairy cows. Theriogenology 2: 451-465 (1987).
MAY 1991 VOL. 35 NO. 5
of early embryo superovulated
1049
OF HEAT
STRESS ON CO~CEPT~DN IN A DAIRY SOUTH AFRICAN CONDITIONS
HERD
HODEL
UNDER
J.H. du Preez,' S.J. Terblanche,2 W.H. Giesecke,' C. Maree3 and M.C. Welding4 IDepartmentof AgriculturalDevelopment,VeterinaryResearch Institute Private Bag X05, 0110 Dnderstepoort,Republicof South Africa Faculty of VeterinaryScience 2Departmentof Theriogenology, Universityof Pretoria,Private Bag X04, 0110 Onderstepoort Republicof South Africa 'Departmentof LivkstockScience,Faculty of Agriculture Universityof Pretoria,0002 Pretoria,Republicof South Africa 48iometricand DatametricServices Departmentof AgriculturalDevelopment Private Bag X640, Pretoria0001, Republicof South Africa Received
for
publication: Accepted:
October 30, 1ggo Febz=uary IO, 1991
ABSTRACT Three regressionmodels are proposed for predictingreproductionin a model dairy herd under South African conditions. Conception rate (CR%) was related to mean monthly temperature-humidity index (THI) by; CR% = to 31,15THf - 0.25TH12 - 890.2, and first service conceptionrate (FSCRX) THI by; FSCR# = 173.45 - 1.79THI. Conceptionrate was related to numerical month of the year (M) by; CR% = 11.86&l - 0.82M2 + 26.36. The relation between mean monthly THI values and the conceptionrate of dairy cattle is Further investigations to test the proposed regression significant. models under various dairy herd conditionsand to improve reproductionin South African dairy herds are needed.
Key words: conceptionrate, first service conception rate, heat stress, temperature-humidity index INTRODUCTION High sensible temperature and humidity are associated with seasonal declines in the reproductiveefficiencyof domestic cattle (I-2). From literature referred to by Du Preez et al. (31, Giesecke (4) and Hahn (5) it is apparent that thermal conditionsare a constrainton the performance of farm animals, particularlyin high-yieldingdairy cattle. The effects of thermal stress on reproductionmanifest themselvesin several physiologic mechanismsand include debilitating effects on conceptionrates, duration and expressionof estrus, etc. (6-9). At present, the temperstureAcknowledgments The authors thank Mrs. C.A. Smith for
typing of the manuscript, Mr. A. Kruger for data processing and the Department of Agricultural Development for financial support.
MAY 1991 VOL. 35 NO. 5
1039
THERIOGENOLOGY humidity index values are the most practical means of assessing the exposure of cattle to heat stress (IO). Warmmonths are more closely associated with lower conception rates than cool months (1). The average tempersture-humidity index of the second day before breeding is closely correlated with conception rate (2). The thermoneutral zone for cows is between 0” and 16°C (6). Cows experience heat stress when the temperature rises above 23.8’C at a relative A temperature-humidity index value of 70 or less is humidity of 80% (11). classified as normal; values above 70 are stressful to cattle (12). The Livestock Weather Safety Index (LWSI) indicates that in large areas of South Afxica and Namibia for prolonged periods of the year warm climatic conditions cause heat stress in food-producing animals, especially in dairy cattle, thereby hampering their performance (3, 13). The purpose of this study was to investigate the relation between temperature-humidity index values and conception rate in dairy cattle in Betha1 district, a highly populated dairy area of South Africa, and to determine an equation for the accurate prediction of the conception rate and first service conception rate of dairy cattle under various temperaturehumidity index conditions and et different periods of the year.
MATERIALSANDMETHODS Dairy Herd Model:
Experimental
Animals
The investigation was performed from 1987 to 1989 on a herd of 185 Friesian cattle on the Transvaal Highveld near Bethal (latitude 26’27’5, longitude 29’29’E and altitude 1663 m) in a semi-intensive system. The total number of lactations from 1987 to 1989 was 546, with an average per The herd was machine-milked three times a day. The cows cow of 2.9. varied in age, number of lactations and daily milk yield. Breeding occurThe standard of management, animal husbandry and red throughout the year. All artificial inseminations were dons by two hygiene were excellent. Milk production varied from 4’l’LY to 13165 kg per qualified inseminators. Estrus observation efficiency was good, and obserlactation of 300 days. vations were always performed by the same trained personnel. The calculated mean interval between estrus periods was 24. Cows were culled after the fifth unsuccesfull insemination. Meteorological
Data
Meteorological data were obtained from the South African Weather Bureau Publication WB 40 (14) as described by Du Preez et a1,(3). lhe temperature-humidity index values (Table 1) were calculated according to the methods described by Kibler (15). Reproduction
Parameters
The relationship of reproduction parameters conception rate and first rate to heat stress (temperature-humidity index service conception The reproductinn parameters values) were investigated on a monthly basis. for a five-month period (November until March) with a high (> 7(J) tempeexperienced heat stress, rature-humiaity inoex, during which dairy cattle were compared with a five-month period (May until September) with a low experienced either (< 70) temperature-humidity index, during which cattle no stress or minimal heat stress.
1040
MAY 1991 VOL. 35 NO. 5
4
ul
!! ?
F
Fj
72.9
7O.S
71.9
1908
1909
Mean
69.6s
70.1
71.2
70.5
7Q.3
Mar
67-6
72.0
73.9
Feb
index
63.9
63.4
63.5
64.9
57.7
58,5
5tL3s
56.4
The mean THX values sw
67.0
64.9
66.5
69.5
May
Jun
(THI) values
Months by THI values
temperature-humidity
for that month of that year,
72.2
1987
aNot available
Jan
1989
The mean monthly
‘/ears
Teble 1.
62.4
64.7
62.1
40.5
Au9
1920 to 1984
64.2
65.7
63.4
63.5
Sap
(3$14)
67.2
C&4
68.4
64.8
Ott
69.6
69.6s
69.6s
69.7
NW
to the dairy herd modsl at Betha
for the period
57.8
58.0
58.0
57.3
Jul
applicable
71.3
71.08
71.0s
71.8
Dee
For 1987 to
THERIOGENOLOGY Classificationof Temperature-humidity Index Values The temperature-humidity inaex values were classifiedaccordingto the LWSI of the Livestock Conservation Institute (12) to evaluate whether dairy cattle were heat stressed:Temperature-humidity index of 70 or less indicatednormal LWSI level, 70 to 78 indicatedan alert level, 79 to 83 indicateddanger level and 83 or above indicatedan emergencylevel. StatisticalMethods A polynomial of a suitable degree was fitted to the data (1987 to 1989, Table 2) by means of a polynomialregression(16). Three regression models were fitted to the data. The first regressionmodel was used to predict conception rate percentage (CR%) according to the mean monthly temperature-h~idityindex values. The second regressionmodel was used to predict the conceptionrate percentageby numericalmonth of the year; and the third regressionmodel was used to predict the first service conception rate percentage (FSCff%) according to the mean monthly temperature-humidity index values. Predictionof ConceptionRates The monthly and five-monthlymean conceptionrates for dairy cattle according to the equation: CR% = 38b.3 - 4.62THI (Z), and the three regression models as describedunder statisticalmethods were investigated and used to predictconceptionrates and first service conceptionrates. RESULTS PolynomialRegressionModels The second order polyn~ial regressionof the monthly true CR on the mean monthly THI data (Figure 1) gave: CR% = 31.15THI - 0.25TH12 890.2. This model explains73X of the variationin CR fR2 = 0.726). The second order polynomialregressionof the monthly true CR on the numerical month of the year (Figure 2) gave: CR% = 26.36 + 11.86M - O.8ZM2. This model explains 74% of the variationin CR (R2 0.737). The second order polynomialregressionof the monthly true FSCR on the mean monthly THI data (Figure 3) gave: FSCRX = 173.45 - 1.79THI. This model explains 58% of the variationin FSCR (R2 = 0.576). q
DISCUSSIUN The mean actual monthly conceptionrate and first service conception rate were at their lowest (36.4% and 32.8%) in January, while the mean monthly temperature-humidity index value was at its highest (71.9). The first service conceptionrate was at its highest (73.5%)in June while the monthly t~perature-humidityindex value was at its lowest. There was a decrease of conception rate with increasing temperature-humidity index The data applicableto the dairy herd model (Table 2) values (Table 2). indicate distinct trends,due mainly to an inverse nonlinearrelationship between the temperature-humidity index and conception rate (Figure I), temperature-humidity index and numericalmonth of the year (Figure 2) and temperature-humidityindex and first service conception rate values (Figure 3). Ingraham et al. (17) showed that the conceptionrate of 191 cows serviced on days with an average temperature-humidity index below 66 was 67% compared with 21% for cows serviced on days with an average temperature-humidity Index above 76. 1042
MAY 1991 VOL. 35 NO. 5
5 tn
kl
g
f
37.4
44.3
PFSCR (%)d
45.7
46.0
44.1
SE.4
46.9
46.8
47.6
54.6
49.3
63.5
56.7
55.0
70.1
Mar
regression
54.6
60.7
62.7
Ml.5
40.7
60.8
67.0
Apr
Months by values
different
(P)
index
(THI)
57.8
57.7
73.5
68.1 69.8
61.0
65.2
120.8
69.4
69.4
65.6
119.9
65.0
60.0
Jul
70.0
actual
conception
62.5
69.0
68.6
101.8
70.0
83.0
62.4
Aug
as FSCRI applicable
Jun
65.2
68.2
98.2
59.4
67.0
63.9
May
CR% as well
equations
of
and corresponding
model
values
rate
56.2
53.2
60.6 63.3
64.7
77.8
62.2
54.5
67.2
act
dairy
(CR%), the
66.9
85.7
52.1
64.2
64.2
Sep
to
to the equation: CR% q 388.3 - 4.62THI (2). to the regression equation model: CR% = 31.15THI - 0.25THI2 - b50.2. to the regression equation model: CR% : 26.36 + 11.86M - 0.822. M = month of the year in numerical to the regression equation model: FSCR% = 173.45 - 1.79THI. true CR and FSCR are 59.2 and 55.3%. 50.7% for the hot months frjov to Mar) and 68.4% for the cool months (May to Sepf. FSCR% was 48.6% for the hot months (Nov to Mar) and 62.2% for the cool months (May to Sep).
40.9
PCR (%,)b
PCR (%)=
a&cording bAccording “According dkcording The overall The CR was The actual
32.8
54.7
FSCR (7;)
PCR (%)a
71.9
36.4
71.2
by means of
Feb
1989
and predicted
temperature-humidity
CR% (FSCffi)
Jan
to
service
THI
1987
first
The mean monthly
CR (%)
data
monthly
Mean
Table 2.
Nov
model
order.
49.0
58.0
52.7
67.2
50.0
57.4
69.6
herd
mean monthly
true
46.5
51 .o
46.6
60.7
53.8
55.2
71.3
Dee
for
Figure
I
I
I
I I
I I I
>- - .k_?
I
I
I
----Y_ -. -. \.
\
‘_---
\
I
‘_-----.
.
I
.
.
\
\
-.--\
I
\
\
I
‘-
I
A’\ \ \. \ \\
‘\ \
\
The actual according CR --, actual
CR ---
and
rates values. predicted
and predicted conception to the mean monthly THI
:
Ingraham’s
= 31.15THI Legend CR --.
(CR%
(14)
0.25TH12
890.2) predicted
-
56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 Temper&we-humidity index
-
1.
30
40
50
60
70
80
90
Figure
2.
0
20
40
60
80
100
actual
Feb predicted
the numerical CR --.
and month
conception of
the
rates
Legend
= 26.36
:
Ott
Actual
c 11.86M
Ang Sep (CR%
year.
Jul
MOIlth
Mar Apr May Jun
according to and predicted
The
Jan
0.82N2) CR ---
-
,.
Nov Dee
” *E_*--,-
”
THERIOGENOLOGY
1045
MAY 1991 VOL. 35 NO. 5
THERIOGENOLOGY Temperature-humidity index values grouped accordingto the categories of the Livestock Wheather Savety Index (12) and the Livestock Wheather Savety Index for lactatingdairy cattle (6,7) suggest that within the nor-ma1 range of temperature-humidity index values of up to 70, dairy cattle show optimal performance,experience no significantheat stress and are not aaversely affected by handling (101. Johnson (IS) showed that the critical temperature-humidity index value for milk productionis 72. The temperature-humidity index threshold for reproouctionseems to be in the region of 65 for conceptionrate and 62 for first service conceptionrate (Figures1 and 3). It is apparentthat heat stress affects the conception rate and first service conceptionrate long before the temperature-humidity index rate reaches 72, when milk yields start to drop significantly. The predicted conception rates according to the mean monthly temperature-humidityindex and numerical month of the year compare favorablywith the actual mean monthly conceptionrates (Table 2). Ulberg and Burfening (19) showed that a I'C increase in rectal temperaturein COWS within 12 h after inseminationreduced the pregnancyrate from 61 to 45%. Warm months were more closely associatedwith lower conceptionrates than with cool months; month effects appeared to be accountedfor by the climatologicalmeasurements (20). Wolfenson et al. (21) showed that conceptionrate was higher in cooled than in noncooledcows (59 vs. 17X). Fertilizationis normal in heat stressedcattle (8) so embryonicdeath is responsiblefor decreasingconception rate of cattle in hot climates ($9). Nonty and Racowsky (22) suggest that the reduced fertilityof summer heat-stresseddairy cows may result from decreased viabilityand developmentalcapacityof Cay-6 to Gay-8 embryos. The mechanismsunderlying these observedadverse effects of heat stress survivabilityof embryos are unknown, but they may be due to a direct action of heat on the embryo or to an indirect effect that is mediated by the uterine environment. Heat stress between Days 8 to 17 of pregnancy altered the uterine environment as well as growth and secretory activity of the conceptus. Conceptuses were lighter, and the uterine environmentwas either unable to support embryo developmentor was toxic to the embryo (19). The new regressionmodel (CR% = 3?.15THI- 0.25THIz- Cr90.2) provided fairly accurate predictionsof conceptionrate (Table 2, Figure I> and is recommendedfor South African conditionsinstead of the formulacalculated by Ingraham (17). Predictingconceptionrate according to the month of the year is not recommended,because it can be used only under similar climatologicalconditionsand is insensitiveto changes in actual temperature-humidityindex values. The new regressionmodel (FSCRX = 173.45 1.79THI) to calculate the first service conceptionrate if the temperature-humidityindex values are known can also be used to great advantage under Southern African conditions. Precautionsagainst heat stress such as shade, air movement,cooled drinking water, diet alterations,wetting and the like (13) can possibly improve conceptionrate and first service conceptionrate in the Bethal district of South Africa. The calculated formulaeto predict conceptionrates under SouthernAfrican conditionscan be used to implementshort, medium and long term precautionsagainst heat stress in dairy cattle with low conceptionrates. In conclusion,preventative animal husbandry and management precautionsagainst heat stress, which may increaseconceptionrate and first service conceptionrate, can be taken in areas in South Africa, where reduced conception rates and first service conception rates are predicted with the regressionmodels Further according to the te~erature-huinidity index values, investigationsof the effect of heat stress on reproduction of dairy cattle in South Africa are suggested. MAY 1991 VOL. 35 NO. 5
1047
THERIOGENOLOGY REFERENCES 1.
Gwazdauskas,F.C., Thatcher,W.W. and Wilcox, C.J. Physical,environmental, and hormonalfactorsat inseminationwhich may effect conception. J. Dairy Sci. -56: 873-077 (1973).
2.
Ingraham,R.H. Discussionof the influenceof environmentalfactors on reproductionof livestock. &: LivestockEnvironment,Proceedings of the InternationalLivestockEnvironmentSymposium,SF-01-74, AmericanSocietyof AgriculturalEngineers,St Joseph,Michigan,1974, p. 55.
3.
Du Preez, J.H., Giesecke,W.H. and Hsttingh,P.J. Heat stress in dairy cattle and other livestockunder SouthernAfrican conditions: 1. temperature-h~idityindex mean values during the four main seasons. OnderstepoortJ. Vet. Res. 57: 77-87 (1990).
4.
Giesecke,W.H. The effect of stress on udder health of dairy cows. DnderstepoortJ. Vet. Res. -52: 175-193 (1985).
5.
Hahn, G.L. Menagementand housingof farm animals in hot environStress Physiologyin Livestock,Vol. '2, ments. &: Yousef,M.K.,(ed) Ungulates.CRC Press Inc., Boca Raton, Florida,1985, pp. 151-174.
6.
Bianca, W. Animal responseto meteorologicalstress as a function 4: 119-1315 (1970). of age. Biometerology
7.
Cavestany,D., El-Wishy,A-B, and Foote, R.H. Effect of season and high enviro~ental temperatureon fertilityof Holsteincattle. J. Dairy Sci. 8: 1471-1478(1985).
0.
Drost. M., Thatcher,W.W. Heat stress in dairy cows. Veterinary Clinics of North America:Food Ani. Prac. 3: 609-618 (1987).
9.
Fuquay, T.W. Heat stress as it affects animal production. J. of Ani. Sci. -52: 164-174 (1981).
10.
Yousef,M.K. Stressphysiology: definitionand terminology. In: Yousef, M.K., (ed) Stress Physiologyin Livestock,Vol. 1, BasiF Principles,CRC Press, Inc., Boca Raton, Florida,1985, pp. 3-7.
11.
Nickerson,S.C. Mastitismanagementunder hot, humid conditions.&: Proceedingsof the Dairy Hsrd ManagementConference,Macon GA, 1987, pp. 32-38.
12
Anonymous. InformationRelease. Patternsof TransitLosses. Livestock ConservationInc., Omaha, NE, 1970.
13
Du Preez, J.H. and Giesecke,W.H. Die uitwerkingvan hittestresby melkbeeste. South African Vet. Med. 3: 28-35 (1990).
14.
Weather Bureau Departmentof EnvironmentalAffairs. Climate of South Africa, ClimateStatisticsup to 1984, WB 40. GovernmentPrinter, Pretoria (1988).
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MAY 1991 VOL. 35 NO. 5
Environmental physiology and shelter enigeneering. 15. Kibler, H.H. Thermal effects of various temperature-humioity combinations LXVII. of Holstein cattle as measured by eight physiologicsl responses. In: Research 8ulletin Missouri Agriculatural Experiment Station, 564, p. 862. 16. Draper, N. and Smith, H. Applied regression Wiley & Sons, New York, 1981, pp. 266-273. 17.
snalysis.
2nd ed.,
John
Ingraham, R.H., Gillette, D.0. and Wagner, W.D. Relationship of temperature and humidity to conception rate of Holstein cows in subtropical climate. J. Dairy Sci. 7: 476-481 (1974).
18. Johnson, H.D. Physiological responses and productivity of cattle. Yousef, M.K., (ed) Stress physiology in livestock, Vol. 1, Basic ciplea, CRC Press, Inc., Coca Raton, Florida, 19b5, pp. 4-19.
In: Prs-
19. Ulberg, L.C. and Burfening, P.J. Embryo death resulting from adverse environment on spermatozoa or ova. J. Ani. Sci, -26: 571-577 (1967). 20. Gwazdauskas, F.C., Wilcox, C.J. and Thatcher, W.W. Environmental managemental factors affecting conception rate in subtropical J. CIairy Sci. -58: 88-92 (1975). climate.
and
21. Wolfenson, D., Fla~nbaum, I, and Berman, A. Hyperthermia and body energy store effects on eetrus behaviour , conception rate, and corpusluteum function in dairy cows. J. Dairy Sci. 2: 3497-3504 (1988). 22. Monty, D.E. and Racowsky, C. In vitro evaluation viability and development in summer heat-stressed, dairy cows. Theriogenology 2: 451-465 (1987).
MAY 1991 VOL. 35 NO. 5
of early embryo superovulated
1049