Heat-stress responses of temperate and tropical breeds of Bos taurus cattle

Abstract

Two breeds of Bos taurus cattle from temperate (Angus, A) and Tropical (Romosinuano, RS) environments were tested with their F1 cross (C) to determine specific thermoregulatory responses to heat challenge under controlled ambient conditions. All animals were exposed to two separate challenge sessions of 6-7 days duration each, with an ambient temperature increase from 24.4-25.6 to 31.1 – 32.2 °C. Rectal temperature and respiration rate were recorded daily during each challenge session. In addition, cutaneous water vaporization rate and selected surface temperature were measured during the thermoneutral rest period between sessions and the peak themal load of the second challenge. Heat exposure produce a larger increase in rectal temperature of A than either RS or C. the superior heat tolerance ability of RS relative to A breed was attributed to a greater increase in cutaneous evaporative water and less physical insulation to imped heat loss. There were no significant heat exchange differences between A and C to explain the superior homeothermic ability of the latter type during heat challenge. It is possible that the first generation cross between RS and A cattle utilize another thermoregulatory process that was no measured in this study (e. g. reduced metabolic heat production) to maintain thermal balance under these conditions.