Abstract:
Rectal temperatures, respiration rates, cutaneous evaporation rates, and skin temperatures were measured in Brahman cross, buffalo, Banteng, and Shorthorn steers exposed to sun at 31-32�_C dry bulb and 40-46�_C globe thermometer temperatures during April and September. The animals were also subjected to forced exercise lasting 45 minutes. The buffaloes were judged to be least heat tolerant in both stationary and exercise trials with the Shorthorns showing the second highest rectal temperatures as a result of the imposed heat stresses. The heat tolerance of Brahman crossbreds and Bantengs differed little in the stationary trials, but the latter species were more stressed by forced exercise. Cutaneous evaporation rates were higher in Bantengs than Brahman crosses, suggesting possible differences between these two species in their methods of heat dissipation. The buffaloes appeared to be least capable of increasing their cutaneous evaporation when under heat stress. The results are discussed in the light of existing knowledge about the differences between species with respect to heat dissipation, heat production, and resistance to heat uptake.