Responses of Steers to Water Restriction

An investigation was made into the effects of dehydration induced by withholding drinking water on various metabolic and thermoregulatory functions of steers, both in a temperate (15°C) and in a hot (40°C.) environment. During 4 days of dehydration at 15°C decreases occurred in food intake, the excretion of faeces and urine, evaporation, body weight, heat production, respiratory ventilation, plasma potassium and in urinary potassium output. At the same time increases were found for haematocrit, plasma total solids, plasma sodium, plasma chloride and blood urea, and in the output of urinary sodium. During 2 days of dehydration at 40°C, qualitatively similar changes occurred in most of these variables. The rapid ingestion of large amounts of water at the end of each dehydration period caused dramatic but transient changes in many of the quantities investigated. Some of these changes were related to shivering which followed drinking in the temperate, but not in the hot, environment. The repayment of the water debt accumulated during dehydration occurred very rapidly, most of it within the first day of dehydration. The restoration to normal of the various physiological values deranged by dehydration, required more than 1 day in most instances. There did not seem however, to be permanent changes nor any impairment of health due to the relatively short period of dehydration. The results arc discussed in relation to mechanisms involved in water balance and temperature regulation.