Fluid balance in food-deprived lactating goats drinking saline.

Fluid balance was studied in four lactating goats during two 3 week periods, which included 30 h periods of food deprivation. In one period the goats were given 0.9% NaCl to drink, and in the other they were given water. Prior to food deprivation, fluid intake and urinary flow were similar in the two groups, but urinary Na+ excretion was higher in the saline-drinking goats. The plasma renin activity was depressed in saline-drinking goats, while the plasma aldosterone concentration was the same both in saline-drinking and water-drinking animals. Food deprivation depressed fluid intake and urine flow in all goats, but the reduction was more pronounced in goats drinking saline. The urinary Na+ and K+ excretion also decreased, in both groups, as did plasma Na+ concentration and osmolality. The plasma protein concentration increased in both groups, indicating that hypovolaemia had developed. The renin-angiotensin-aldosterone system (r.a.a.s.) became activated in goats drinking water, but not in the group drinking saline. It is suggested that sodium retention may have attenuated the activation of the r.a.a.s. in the latter group. The results of this study show that hyponatraemic hypovolaemia develops during starvation in lactating goats, regardless of the sodium state of the animals. The possibility that the hyponatraemic hypovolaemia is secondary to an impeded Na+ and fluid absorption from the rumen reticulum is discussed.