REPRODUCTIVE PERIOD AFFECTS WATER-INTAKE IN HEAT-STRESSED DEHYDRATED GOATS

Water intake following dehydration was studied in pregnant (N = 5), la ctating (N = 4) and nonpregnant, nonlactating (N = 5) Swedish domestic goats (Capra hircus) to investigate if reproductive period affected d rinking. Plasma cortisol concentration and the hematocrit value were m easured to evaluate stress. The goats were water deprived from 9.00 h until 15.05 h the next day. They were fed at 7.00 and 15.20 h. On the second day, ambient temperature was increased from 20 degrees C to 38- 39.5 degrees C for 5.15 h to accelerate water losses. Water temperatur e during rehydration was 35 +/- 1 degrees C. Plasma Na concentration a nd osmolality increased most in dehydrated and heat-stressed pregnant and lactating goats. Pregnant goats lost 2.2 kg of their body weight. They drank 3.5 l immediately, followed by 2.5 l during afternoon eatin g. Lactating goats lost 4.9 kg and drank 6.3 l at once, and 3.9 l duri ng feeding. Nonpregnant, nonlactating goats lost 1.7 kg and drank 2.6 l followed by 0.6 l. The large water consumption in pregnant and lacta ting goats caused hyponatremia and hemodilution, but they continued to drink during the night (0.5 +/- 0.2 l and 0.8 +/- 0.5 l, respectively ). Renal free water clearance increased in all periods, with a long la sting water diuresis during pregnancy. Plasma cortisol concentrations and the hematocrit values rose in connection with water intake. These results imply that the thirst center became less sensitive to inhibito ry signals from the oropharyngeal tract and the diluted blood plasma d uring pregnancy and lactation. Catching sight of water was the most ex citing procedure during these experiments.