The effects of heat exposure (31 degrees C) on Zebu and Scottish Highland cattle.

Abstract

Three Zebu and three Highland mature heifers were used to study the effect of a moderately high environmental temperature (31°C) on temperatureregulatory responses of cold- and heat-tolerant cattle to thermal stress. Following a 7-day period of adjustment to 31°C, the Highland heifers decreased their internal heat production by decreasing feed consumption by 31% and oxygen consumption by 19%. They also increased their evaporative heat losses by an increased respiration rate of 92% and total vaporization (33%). At 31°C, water consumption increased 190% and body fluid compartments showed a significant increase, with the exception of plasma volume. The Zebu decreased feed consumption by 19%, increased respiration rate 100%, total vaporization 80%, water consumption 58%, and plasma volume by 17%. The Highland cattle could not prevent hyperthermia upon exposure to the moderate high temperature, while the Zebus maintained normal rectal temperature. Breed differences in ability to maintain homeothermy are documented in this study.