The influence of environmental temperature and rainfall on the water intake of sheep consuming mulga (Acacia aneura).

Abstract

Animal Production in Australia THE INFLUENCE WATER OF ENVIRONMENTAL OF SHEEP TEMPERATURE MULGA AND RAINFALL ON THE INTAKE CONSUMING (ACACIA - ANEURA). - N.P. McMENIMAN* and SUMMARY P.M. PEPPER** The water intakes of sheep consuming mulga with and without supplements of phosphorus and/or molasses were monitored along with environmental temperature and rainfall during a period of eleven months. Relationships were developed which showed that variation in maximum daily temperature explained 44% to 71% of the variation in water intake. Rainfall depressed water intakes of sheep that were not receiving a molasses supplement. Phosphorus and molasses supplements consistently increased water intakes at all temperatures. INTRODUCTION That sheep consuming mulga require an adequate supply of good quality drinking water has long been recognised by sheep managers. However, apart from the mean figures presented by McMeniman and Little (1974) no information is available to indicate the precise water requirements of sheep consuming a mulga diet. The water intake, environmental temperature and rainfall data collected in the experiment reported by McMeniman and Little (1974) have been further examined so that water requirements of sheep fed mulga can be more precisely predicted. MATERIALS AND METHODS A detailed description of the experimental procedures followed are contained in the report by McMeniman and Little (1974). On the Charleville experimental reserve fifty-eight maiden Peppin Merino ewes were randomly allocated to and run in each of eight 60.8 ha. paddocks in which mulga was the on)ly forage available. The treatments imposed were supplementation with molasses (M) at the rate of 454 g head-l day-l, phosphorus (P) in the form of monosodium orthophosphate dissolved in the drinking water at a concentration of 1.47 g L-l and phosphorus and molasses (P + M) at the same rates as above. A fourth group acted as an unsupplemented control. The treatments were replicated twice. The drinking water was obtained from a non flowing artesian bore. Water was supplied to the control and M groups from a 20,000 litre galvanised iron storage tank to 3 m galvanised iron drinking troughs: the water flow was monitored with domestic water meters. In the P and P + M groups the phosphorus supplemented water was delivered to 3 m concrete troughs from graduated fibre glass tanks. The total quantity of water used in each paddock was recorded weekly with no allowance being made for evaporative losses from the troughs; initial observations indicated that these would be small (1% of total water consumption). Daily recordings of maximum air temperature and rainfall were obtained from the Charleville Meterological Station which is situated 3 km from the experimental site. A mean value for maximum daily temperature was then calculated for periods which corresponded to the intervals during which water intakes were averaged, while for rainfall the total quantities falling during these intervals weretabulated. * Qld. Dept. of Primary Industries. Present address: Dept. of Animal Production, University of Queensland, St. Lucia, Brisbane, 4067. ** Qld. Dept. of Primary Industries, G.P.O. Box 46, Brisbane, 4001. 443 Animal Production in Australia The records examined in this report cover the first eleven months of the experiment reported by McMeniman and Little (1974) (1st September to 1st August, 1970); during the last four months of this period the ewes were pregnant. The statistical analyses tested for relationships between water intake and maximum daily temperature and rainfall. RESULTS Analysis of the water from the bore head showed that it contained 0.108% total soluble salts and these were comprised of 0.003% calcium and magnesium bicarbonate, 0.053% sodium bicarbonate, 0.021% sodium sulphate and 0.031% sodium chloride. Adding monosodium orthophosphate to this water raised the total soluble salt concentration to 0.664%. The range of maximum daily temperatures during the observation period was 18 to 37OC while the highest rainfall recorded during any weekly period was 70 mm. The observed average water intakes of the control, P, M and P + M groups were 1.48, 1.73, 1.93 and 2.5 L head-' day-l respectively. From 44% to 62% of the variation in water intake in the four treatments was explained by linear relationships between this parameter and maximum daily environmental temperature (Fig. 1). Inclusion of the quadratic function of maximum temperature significantly improved the prediction in the M and P + M but not the control and P groups. Conversely, inclusion of rainfall as a predictor explained significantly more variation in the control and P but not the M and P + M groups. These preferred relationships for predicting water intake are shown in Fig. 2. In plotting the regression lines A and B rainfall was given the mean values of 7.6 mm. It can be seen from these relationships that for every 10 mm of rain that fell within a seven day recording period the water intake of control and P supplemented sheep was reduced by 130 and 110 ml head-l day-l. 2 Comparisons between groups using equations with the terms T, T and R showed that the intake in the P + M group was consistently higher than in the other groups at all temperatures. The control group drank consistently less than the P or M groups but the difference in the case of the P group was not significant. DISCUSSION The results presented show that approximately 50% of the variation in water intake in this experiment where the sheep were grazing under normal drought conditions can be explained by changes in maximum environmental temperature; a similar association with sheep in pens was noted by Clark and Quin (1949). It has been shown that the ingestion of mineral salts increases water consumption by approximately 29 ml g salt-l (Wilson and Hindley, 1968). The average daily monosodium orthophosphate ingestion in the P group was 10 g head-' day-l and when compared with the control group, this was associated with an increased water intake of about 250 ml day-l- (Fig. 1). This indicates that all of the increase in water intake in the P group can be explained by increased salt intake. While the ash content of the molasses used in this experiment was not determined, it has been reported (Whytes et al. 1978) that the average concentration is 13.6% of DM and the mean DM content is 76.4%. Therefore, the molasses supplemented sheep would have been consuming about 47 g soluble salts from this source and this could have been associated with the increased water intake recorded in the M and P + M groups. 444 Animal Production in Australia 15 Maximum daily temperature, C. Fig. 1. 1. 2. 3. 4. 20 25 30 35 40 The linear relationships between maximum ambient temperatures and daily water intake: 2 Control (0) WI = -0.164 (+- 0.324) = 0.060 (+ 0.012) T, r = .45 2 WI = -0.217 (+ 0.383) + 0.071 - 0.014) T, r = .44 (+ p (VI 2 WI = -0.118 (+ 0.381) + 0.074 (2 0.013) T, r = .47 M (A) P+M() WI= 2 0.050 (2 0.340) + 0.089 (2 0.012) T, r = .62 where WI is water intake (L/head/day) and T is maximum daily temperature, 'C. 445 Animal Production in Australia Water requirements are known to be influenced by a large number of f-actors including physiological state of the animal, diurnal variations in environmental temperature, grazing behaviour of the animals, fleece length and level of nutrition. None of these factors could be allowed for in the analyses presented and undoubtedly variations in some or all of them would have contributed to the unexplained variations in water intake. At the maximum temperature recorded in this experiment (37�C) it can be calculated (Fig. 2) that the maximum water intake of the unsupplemented (control) sheep was 2.3 L head-l day-l while in the P + M group it was 3.3 L head-1 day-l. If the relationships are extrapolated to 42OC, a temperature that would not be unusual under practical mulga feeding conditions, the calculated water requirements of the control and P + M groups then become 2.6 and 4.7 L head-l day-l respectively. It is now known that approximately 50% of the production response obtained from a molasses supplement in mulga fe,d sheep can be obtained with a sulphur supplement (see Gartner and Niven, 1978); the substitution of a sulphur salt for molasses would be unlikely to increase the water requirement. REFERENCES CLARK, R. and QUIN, J.I. (1949). Onderstepoort J. Vet. Sci. GARTNER, R.J.W. and NIVEN, D.R. (1978). Aust. J. Exp. Agric. McMENIMAN, N.P. and LITTLE, D.A. (1974). Aust. J. Exp. Agric. WILSON, A.D. and HINDLEY, N.L. (1968). Fld. Stn. Rec. Div. (Aust.) = 25. 7: WYTHES, J-R., WAINWRIGHT, D.H. and BLIGHT, G.W. (1978). Aust. Hush. 18: 629. E Anim. Ind. 22: 345. Anim. Husb. 18: 768. Anim. Husb. 14: 316, Pl. Ind. C.S.1~TO. J. Exp. Agric. Anim. 446