Fluid balance during food deprivation and after intraruminal loads of water or isotonic saline in lactating and anoestral goats.

A study was made of water and salt balance during a 28 h period of starvation in lactating and anoestral goats. Food deprivation caused diminished water intake in all but one animal, and the secretion of urine and milk gradually decreased. The plasma volume and the glomerular filtration rate were reduced, the plasma Na concentration lowered, and the plasma renin activity and plasma aldosterone concentration raised during starvation. After 28 h without food the goats were given a load of water or saline into the rumen. The fall in the plasma protein concentration that occurred indicates that the plasma volume increased in all animals within 4 h of receiving saline, but was unchanged after the water load. The plasma Na concentration decreased further after the water load, but increased in all animals after the saline load. The plasma renin activity and plasma aldosterone concentration remained elevated after the intraruminal water load, but fell towards basic values after the saline load. The renal Na excretion decreased during food deprivation, and showed no increase within 4 h of saline loading. It appears that only the load of saline restored the salt and water homoeostasis of the animal. Lactating and anoestral goats do not apparently differ in their response to starvation. The effects of starvation on fluid balance seem to become as severe in goats as in monogastric species despite food reservoirs in the reticulo-rumen and omasum at the onset of food deprivation.