Animal Production in Australia Vol. 15
THE EFFECT OF HEAT AND HUMIDITY ON PREGNANT FERAL GOATS S. Prasetyo*, H.M. Miller, E.A. Scheu and J.H.G. Holmes+
SUMMARY
Six pregnant does were maintained at ambient temperature of 19OC, humidity 52%, fed ad libitum (Group 1); six at 27-35b, 76-49% humidity, fed ad libitum
(Group II), six at 19O, 52% humidity, pair fed with Group II (Group III), all for the last half of pregnancy. Group II and Group I ate the same amount of feed, Group II drank twice as much water in week 21. Respiration rates were I, 44;
II, 123; 111, 50 (P<.OOl) pulse I, 99; II, 100; III, 110 (P<.OOl) and temperature I, 39.2 ; II, 39.6 ; III, 38.9 (P<O.OOl). Cortisol was not increased in Group II Food intake, dam weight gain, age, gestation length, respiration, pulse, cortisol concentration did not contribute significantly to the relation.
Litter Wt (Kg) = 1.55 (Litter size) + 0.46 (No. of males) + 0.041 (Weight of Dam) - 1.37 (Temperature of Dam)
-I- 52.744, (Multiple correlation coefficient 0.953, P<O.OOl).
The effect of heat stress in goats may operate through increased body temperature, with a reduction in litter weight of 137g/0.1°C, even at a level of stress too slight to affect appetite.
INTRODUCTION
Heat stress during pregnancy adversely affects foetal development in many species. Under field conditions, the susceptibilities of different species of grazing animals varies; for example, in the humid lowlands of P.N.G., cattle produced calves of normal weight and vigour while Priangon sheep produced weak, undersized lambs which suffered high mortality (Holmes 1980). Although goats outnumber sheep in many areas of the humid tropics, their susceptibility to heat stress has not been studied as much. This paper reports a "hot-room" study of the response of Australian feral goats to moderately high temperatures and high humidity during the last twelve weeks of pregnancy.
MATERIALS AND METHODS
The experiment compared three groups of does: Group I fed ad libitum, housed at "thermoneutral" temperatures; Group II, fed ad libitum, housed at temperatures and humidities found in some humid tropical conditions; Group III housed at thermoneutrality, "pair fed" with Group II, assuming that Group II would reduce feed intake. This should allow separation of direct effects of heat and humidity, and indirect effects via effects on intake.
From 27 feral does, aged 2 to 4 years, with known conception dates, 18 does expected to kid over a short period were allocated, on a stratified random liveweight basis, to three groups. At about the seventh week of pregnancy, the does were placed in metabolism cages, on 10:5:82.
Group I and III were housed at 19Oc + Group II was accommodated in a "con trolled and humiditie s were raised, over 21 days, t
2.
cl .o
4 and 52 % + 3.6% rel imate" r 00; in which a regime of:
ative humidity.
temperatures
*Universitas Mataram, Mataram, Lombok, Indonesia.
+School of Agriculture & Forestry, University of Melbourne, Parkville,Vic. 3052.
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0000 hrs - 0600 hrs 27.2O -I- 1.7 76.0 + 4.3% relative humidity 0600 hrs - 1200 hrs 31.7O t 0.9 58.0 t 2.4% relative humidity 1200 hrs - 1800 hrs 34.8' T 0.6 49.0 T 3.5% relative humidity 1800 hrs - 2400 hrs 31.9O t 0.9- 57.3 t 3.9% relative humidity-
These temperatures and relative humidities were maintained from the beginning of June until kidding, which occurred in mid-August.
All animals were fed pasture hay (Brome grass, Ryegrass and subterranean clover); Groups I and II were fed ad libitum; Group III does were pair fed with Group II animals. Water was always available.
Measurements included:
Liveweight every two weeks and one day post partum. Feed and water intake, daily;
faecal and urine output for the 13th and 18th weeks of pregnancy. Rectal
temperature, respiration and pulse rates at 0400 hrs, 1000 hrs, 1600 hrs and 2200 hrs, on one day each week. Cortisol in jugular blood plasma, sampled once each week for the last five weeks.
One week before parturition was due, all does were transferred to lm x .9m pens I with straw bedding, in the same room; temperature and humidity were maintained. Kids were weighed as soon as they were dried by their dams, before the first drink.
Group data were analysed by Analysis of Variance, and differences tested by Newman-Keuls' method.
RESULTS AND DISCUSSION
The distribution of litter size and sex of kids (Table 1) included four sets of twins per group. Since differences per group in intakes were large and unequivocal, intake results (Table 2) are presented for the twelve twin-bearing dams only. Liveweight ranged from 28Kg for 2 year old does to 48Kg for 4 year olds; intakes are also presented per unit metabolic size.
Table 1 Distribution of litter size and sex of kids in three groups of feral does
Dry matter intake was not reduced by the increased temperature and humidity.
Some of the "pair fed" group did not consume their entire ration. In each group, intake increased by nearly 50 % during the experiment, but fell slightly just before parturition. Digestibility of the ration was not affected by treatment.
"Hot room" does drank twice as much water as Group I animals. Urine volumes were too variable to permit any conclusions. All groups increased water intake by about 50% over this period. N retention and weight gains were not significantly
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different for different groups during the periods of measurement.
Table 2 Intake of feed and water, digestible organic matter content of dry matter (DOMD), urine output, N retention and weight gain of doe
(- conceptus) for twin-bearing feral does in late pregnancy (mean of four does per group)
a, b means with different superscripts differ (P~O.001)
The major response to the heat stress was a large increase in respiration;
the respiratory cooling was inadequate and rectal temperatures rose (Table 3).
Mean temperatures of individual does in Group II ranged from 39.04'to 39.60°
and these paralleled changes in pulse and respiration. These differences may be due to differences in animal response or to undetected variation in heat load at different points in the hot room. Significant circadian fluctuations
occurred in rectal temperature and respiration.
Table 3 Respiration, pulse rates and rectal temperatures in late pregnancy in twin-bearing does
For each parameter, differences between groups and weeks were highly significant (F<3.001).
Cortisol concentrations were slightly lower in the heat stressed does and did not rise before parturition. Within Group III some animals showed consistent high values throughout; in Groups I and III does with low values experienced a larger rise than those with high values (Table 4).
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Table 4. Cortisol concentrations in twin-bearing does during the last five weeks of pregnancy (ng/ml of plasma)
a, b Values with different superscripts differ @<O-05)
Litter weight was analysed by stepwise regression on the indices of strain in the individual animals, (temperatures, respiration rate, etc.) rather than by analysis of variance of the three groups, since the stress imposed was not associated with identical strain. Additionally, litter weight is known to be related to litter size, number of male kids, and dam weight (Amoah and Bryant, 1983). Age of dam and gestation length are associated with dam weight and did not significantly improve the multiple regression when dam weight was included.
Rectal temperature had a highly significant regression coefficient (F<O.OOS) and after temperature was included, respiration, pulse and cortisol concentration were not significant. Digestible energy intake, D.E.I. above maintenance and weight gain of dam were not significantly related to litter weight. In fact, the mean weight of twins in Group III was heavier than from Group I. The final regression was:
Litter weight (Kg) = 1.55 (No. of kids) + 0.46 (No. of males) - 1.37
(rectal temperature of dam) + 0.041 (Weight of dam) + 52.744 (Multiple regression coefficient 0.953, P<O.OOl).
We conclude that heat and humidity stress has its deleterious effect on pregnant goats, by a direct effect on body temperature. There was no relation between heat stress, intake of feed and litter weight. Cartwright and Thwaites
(1976) found similar results with sheep. The low cortisol levels throughout the last five weeks of pregnancy in "hot room" does suggest that at this time they were not experiencing strain (unless they were suffering from adrenal exhaustion induced earlier). Presumably strain was avoided by an adaptive mechanism which protected the doe at the expense of the foetus, such as the switching of blood flow from the uterus to the skin for cooling purposes, as occurs in sheep
(Brown and Harrison, 1981). This would subject the foetus to partial starvation and increased temperature.
REFERENCES
Amoah, E.A. and Bryant, M.J. (1983). Anim. Prod. 36(l) 105.
Brown, D.E. and Harrison, PC. (1981). J. Anim. Sci. 52(S) 1114.
Cartwright, G.A. and Thwaites, C-J. (1976). J. Agric. Sci. Cart-b. 86 573.
Holmes, J.H.G. (1980). "Animal Genetic Resources in Papua New Guinea.
Proceedings of a SABROA Workshop on Animal Genetic Resources in Asia and Oceania. T.A.R.C. Tsukuba, Japan .p. 439.
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