THE EFFECT OF SHORT-TERM DEHYDRATION ON KIDNEY-FUNCTION, PLASMA-RENINCONCENTRATION, FECAL WATER-LOSS AND TOTAL-BODY WATER IN SHEEP

Sheep in many areas of the world are exposed to an erratic supply of d rinking water. Also, when they are transported over long distances, se veral days may go by during which they have no access to water. Unless water deprivation is extreme, sheep in general are able to maintain p hysiological homeostasis under relatively adverse conditions, with res pect to their water intake. The aim of this study was to assess the ef fect of acute short-term dehydration on total body water (and several other variables), and to investigate the mechanism of water conservati on under such conditions. Total body water was found to decrease by ab out 20% over the dehydration period. Initially, sodium was lost and el ectrolyte-free water was retained by the kidneys, probably in defence of plasma osmolarity. Later in the dehydration process and during earl y rehydration, renal function changed in that sodium retention increas ed with a corresponding increase in water reabsorption by osmosis, a m echanism more aimed at maintaining total body water constant.