The effect of feeding on evaporative heat loss and body temperature in Zebu and Jersey heifers

Abstract

Some physiological responses to moderate (70–80°F dry bulb and 60–70° wet bulb) ante-room and high (103° dry bulb and 83° wet bulb) hot room temperatures by two Jersey and two Zebu heifers under alternate conditions of normal feed intake and fasting are reported. At moderate temperatures both breeds exhibited a diurnal rhythm in feed and water consumption and in skin temperature, sweating rate, rectal temperature, and respiration rate. In the case of skin temperature, sweating rate, and respiration rate this diurnal rhythm disappeared in the hot room. In the hot room, water consumption increased for all animals. Feed intake was depressed in Jerseys but not in Zebus. In the ante-room, animals tended to have higher sweating rates and rectal temperatures when fed than when not fed. Fed animals did not have uniformly greater skin temperatures in the hot room, but sweating rates, rectal temperatures, and respiration rates were greater. Jerseys had greater sweating rates and lower rectal temperatures than Zebus at ante-room temperatures, but Zebus had greater sweating rates and lower rectal temperatures in the hot room. When fed, Jerseys failed to control their temperatures in the hot room, despite large increases in sweating and respiration rates and a reduction in appetite; whereas Zebus maintained their appetites, and slightly reduced rectal temperatures, by means of their greatly increased sweating rate and a slight increase in respiration rate. Differences between Jerseys and Zebus in sweat gland volume were of the order previously reported for these breeds, and differences in population density were in accordance with differences in body size. The Jersey having the smallest sweat glands also had the lowest number per unit area, and sweated less than its Jersey mate.