The rumen as a water store in sheep

Abstract

The rumen fluid volume in sheep was measured by the method of phenol red dilution. Serial determinations made in 22 sheep deprived of food and water for up to 8 days showed that the greatest decrease in rumen fluid volume occurred during the first 2–3 days, the magnitude of the decrease depending on the initial volume. After the third day, the rate of loss of rumen fluid became slower as the rumen fluid volume became depleted. Sheep deprived of food only gave similar results to those deprived of both food and water. This absorption of rumen fluid during the first 2–3 days of food and water deprivation may account for the expansion of plasma volume which has been recorded on the third day. In a group of eight sheep deprived of food and water for 4 days, the mean rumen volume loss for the period amounted to about half the body weight loss. These results support the view that in the sheep, the water balance of the body proper is kept virtually unaltered by fluid drawn from the alimentary tract during the first days of water deprivation. The animal does not become dehydrated, in the physiological sense, until this reserve is depleted. For this reason, the rumen may be regarded as a water "store" in sheep.