FLUID BALANCE AND MILK SECRETION IN THE FED AND FEED-DEPRIVED BLACK MOROCCAN GOAT

Small, black goats are found in arid and semi-arid regions of Morocco, but physiological adaptations that enable them to thrive in their harsh habitat have not been defined. Six goats (32+/-1 kg) were studied during lactation and nonlactation. Goats were kept indoors (ambient temperature 17-24 degrees C) and studied when fed twice daily, during 48 h of feed deprivation, and after refeeding. The goats were given 800 g concentrates. They ate 740+/-20 g (lactation) and 530+/-30 g/d (nonlactation; P<0.01), indicating that nonlactating goats voluntarily decreased their intake of concentrates. Wheat straw was available ad libitum and lactating goats consumed 230+/-60 g/d, while goats ate 340+/-50 g/d during nonlactation (P<0.05). Feed deprivation caused a 5% weight loss in both groups. Fed lao tating goats drank 1.5+/-0.2 l/d and nonlactating goats drank 1.0+/-0.1 l/d (P<0.05). Thus, the water/DM intake ratio was 1.7 in lactating and 1.3 in nonlactating goats. Water intake was unchanged during the first 24 h of feed deprivation, but then it dropped. Urine volume was not significantly reduced during feed deprivation. Plasma Na concentration decreased, while total plasma protein and haematocrit increased during deprivation, indicating that hyponatraemic hypovolaemia had developed. Plasma aldosterone increased during feed deprivation. Basal plasma glucose was elevated in lactating goats, but decreased during feed deprivation. Basal plasma insulin values were similar in both groups, and dropped during feed deprivation. Plasma urea was the same in both groups before feed deprivation and increased similarly during deprivation. Milk volume was 700+/-48 ml/d. It decreased by 30% the first and 57% the second day of feed deprivation. Two days after refeeding, milk volume was 384+/-81 ml/d. Total milk lactose secretion decreased during feed deprivation in proportion to decline in milk yield. Mean milk fat was 4.2 and 6.2% (at 08:00 and 16:00 h milking, respectively). It increased to 8 and 12%, respectively, during the second day of feed deprivation, and therefore milk fat secretion decreased only 18%. Milk solids content increased in proportion to fat. Milk Na was unchanged during feed deprivation, while milk K decreased. In conclusion, black Moroccan goats had a low water turnover and produced milk with high solids content. In response to acute feed deprivation, they developed hyponatraemic hypovolaemia with a drop in milk secretion like other goat breeds. However, Moroccan goats maintained water intake unchanged during the first stage of feed deprivation.