PREFERENCE FOR DRINKING WARM WATER DURING HEAT-STRESS AFFECTS MILK-PRODUCTION IN FOOD-DEPRIVED GOATS

Food deprivation leads to diminished water intake and decreased milk p roduction in lactating goats. The aim of this study was to determine w hether these effects could be alleviated by offering six lactating goa ts (Capra hircus) warm water to drink at normal or hot ambient tempera tures. The food deprivation period was started on Day -1 at 0700 h by feeding the goats hay but no concentrates. No food was then given unti l 1515 h on Day 0. Between 0700 and 1800 h on Day 0 water was supplied to the goats in three different ways at different ambient air tempera tures as follows: (1) cool (15 degrees C) water in one bucket and warm (35 degrees C) water in another (cool-warm water experiment); (2) coo l (15 degrees C) water in two buckets (cool-cool water experiment); an d (3) warm water in one bucket and cool water in the other in combinat ion with a hot ambient temperature from 1045 h to 1700 h (heat-stress) . Experiments 1 and 2 were performed at room temperature (17.5-19 degr ees C) and at a relative humidity of 60-70%. In Experiment 1, the goat s drank 0.7 +/- 0.61 of the cool water and 5.0 +/- 1.21 of the warm wa ter before re-feeding (P < 0.001). In Experiment 2, the goats drank 1. 5 +/- 0.61 of the cool water. In Experiment 3, they drank more warm wa ter (4.1 +/- 0.81) than cool water (0.51 +/- 0.21; P < 0.001). Body we ight decreased in all experiments during Day -1. It decreased further on Day 0 in Experiment 2, but not in Experiment 1, and in Experiment 3 the goats regained their pre-starvation body weight. The milk lactose concentration fell by 10 and 11 mmol l(-1) in Experiments 1 and 2, re spectively (P < 0.001, afternoon Day -2 compared with afternoon Day 0) , but only by 2 mmol l(-1) in Experiment 3 (NS). The mean milk K conce ntration decreased by 7, 8 and 4 mmol l(-1) in Experiments 1, 2 and 3, respectively. The milk Na concentration did not change in any of the experiments. Milk osmolality did not change despite the drop in milk l actose and K concentrations. Food deprivation reduced milk flow in all experiments, which resulted in decreased secretions of lactose and pr otein in all experiments. The fat secretion did not decrease significa ntly during the heat-stress experiments. It is concluded that offering warm instead of cool drinking water to food-deprived lactating goats increased their water consumption and that this, in combination with h eat stress, counteracted the reduction of the milk secretion. (C) 1997 Elsevier Science B.V.