Regulation of body temperature of sheep in a hot environment

Abstract

A study of the importance of sweating as a means of evaporative cooling in sheep was made by comparing the rectal temperatures of sheep with and without sweat glands, at an air temperature of 40°C and a water vapour pressure of 28.1 mm Hg. The experimental animals, all of which were shorn, comprised 2 ewes and 2 wethers without sweat glands, and 6 ewes and 4 rams with sweat glands. During the first hour the rise in rectal temperature of the sheep without sweat glands was greater than the rise in the normal animals (1.1°C v. 0.7°C). After 6½ hr. the mean rectal temperature was higher (40.6°C) in the sheep lacking sweat glands than in the normal ewes (39.9°C). The most rapid rise in rectal temperature after the first hour was that of the rams, which reached a mean value of 40.8°C. after 6½ hr. It is concluded that panting is the principal method of evaporative cooling in sheep. Sweating, though of lesser importance, is advantageous to the shorn animal, but its usefulness to sheep in wool is unknown.