Sweating rates of cattle in the field and their reaction to diurnal and seasonal changes

Twenty-six replicate observations of sweating rate were made on six Hereford x Shorthorn and six Brahman x Shorthorn steers in the field at different times of day and different seasons. Sweating rates were lower in Brahman cross than in Hereford x Shorthorn steers under mild conditions, but higher under stressful conditions. Brahman cross steers increased sweating rate at lower skin and rectal temperatures. Maximum sweating rates were significantly lower in winter than in summer. This is ascribed to an association between sweating function and other aspects of skin function which undergo seasonal changes. Under cool conditions, either there was no consistent difference between animals in sweating rate as in the Brahman cross steers, or the less heat-tolerant animals with higher body temperatures and thicker coat type showed the higher sweating rates. Under challenging conditions of heat, between-animal differences in sweating capacity were revealed and, in the British steers, animals with higher sweating rates then had lower body temperatures. Furthermore, animals with sleek coats showed a higher sweating capacity despite lower thermal stimulus to the skin. The environmental conditions under which sweating capacity is challenged, when differences between animals become important as a component of heat tolerance, depend upon genotype, season, and duration of heat stress.