The Establishment of Thermal Equilibrium in Sheep Exposed to Cold Environments

Abstract

SUMMARY Eight well trained sheep were exposed to cold environments in a total of 193 experiments, and the temperature of the skin, the trunk and the extremities, rectal temperature and oxygen consumption were recorded. Oxygen consumption was determined by a ventilated mask technique which is described. When the sheep had a fleece depth of less than 15 mm., their rate of oxygen consumption rose during the first 10 min, of exposure to cold to values 71% higher than those established after 60 min., when thermal equilibrium was achieved. An initial transient rise in rectal temperature occurred. When fleece depth was 15 to 25 mm., the immediate rise in oxygen consumption following cold exposure was only 13% higher than that achieved after 80 min. when thermal equilibrium was established. When the fleece depth was over 25 mm., the oxygen consumption of the sheep rose slowly to equilibrium values within 3 hr. and a fall in rectal temperature occurred. The magnitude of the initial rise in oxygen consumption that followed cold exposure appeared to be proportional to the rate of change in trunk surface temperature. The rectal temperature of the sheep in a constant thermoneutral environment was shown to increase by 0·49 ± 0·07°C./cm. increase in fleece depth. The results are discussed in relation to the changes in the body heat content of sheep in natural environments.