Environmental temperature, energy metabolism and heat regulation in sheep. III. The metabolism and thermal exchanges of sheep with fleeces

Abstract

1. Fifteen calorimetric experiments were made with three sheep which had fleeces varying in thickness from 2·5 to 12 cm. All sheep received a constant ration, which corresponded in amount and kind to that given to closely clipped sheep in previous experiments (Graham et al. 1958).2. The metabolizable energy of the food increased with increasing environmental temperature by 2–3 Cal./24 hr./° C.3. Heat production remained constant throughout the range of 15–35° C. environmental temperature. Above 35° C. an increase occurred. At 11° C. a slight rise in heat production occurred in the sheep with a 2·5 cm. fleece. These results show that sheep with fleeces, in contrast to closely clipped sheep, have very wide thermoneutral zones.4. Heat losses by vaporization of water converged to an identical value irrespective of fleece length at 40° C. The rate of increase of vaporization with environmental temperature at lower temperatures decreased as the fleece length increased.5. Respiratory frequencies for given total watervapour losses were the same whether or not the sheep had a fleece.