Respiration in Sheep in Cold Environments

The effects of environmental conditions and the amount of food given on the pulmonary ventilation of sheep were studied using both tracheostomized and normal sheep. When the environmental temperature was lower than the critical temperature of the sheep, pulmonary ventilation increased with increasing ‘coldness’ of the environment. The degree of ‘coldness’ of the environment was assessed by the rate of o2 consumption. The increase in pulmonary ventilation under the above conditions was accounted for by an increase in tidal air volume with little change in respiratory frequency. The o2 content of the expired air fell from more than 18% to less than 16% as oxygen consumption increased from a minimal rate at thermoneutrality to its maximum rate at the summit metabolism. Additional food in thermoneutral conditions increased pulmonary ventilation more than it did o2 consumption, and the o2 concentration in the expired air fell. Additional food in cold conditions had no effect on metabolism or on pulmonary ventilation. The maximal pulmonary ventilation observed in a sheep at the summit of metabolism in a very cold environment was 1442 l./h which is less than half that noted in thermal polypnoea. The observations are contrasted with those obtained in man, where pulmonary ventilation is directly proportional to o2 consumption and the O2 concentration in expired air is virtually constant.