Net energetic and thermoregulatory efficiency during panting in the sheep

Abstract

1. 1. The total heat production and that proportion attributable to panting, together with the total body and respiratory heat loss of shorn Merino sheep, were studied during exposure to various combinations of air temperature and humidity. 2. 2. While exposure to moderately hot environments resulted in panting with mean respiratory frequencies of up to 270 breaths min −1, the total heat production was not significantly higher than that in a thermoneutral environment and therefore the heat produced by panting appeared to be zero. 3. 3. The mean maximum heat loss through panting was approximately 60 per cent of the total heat loss and 56 per cent of the total heat production; this was due entirely to the evaporation of moisture. 4. 4. The results indicate that the sheep relies heavily on panting for heat dissipation and that in moderately hot environments the thermoregulatory efficiency of panting is high. 5. 5. It is concluded that, in the light of more recent observations, the method used here and in previous studies cannot be used to provide an estimate of the energy expenditure due to increased respiratory activity; rather, an estimate of the net change in metabolic rate is obtained.