Heat balance of ox steers (Bos taurus) in steady-temperature environments

Work was undertaken to investigate body heat storage in cattle subjected to steady temperature environments. Heat production (M) of and heat losses (H) from two steers were studied by simultaneous direct and indirect calorimetry over periods of up to 11 days. M and H followed similar trends except after feeding and watering. When the animals stood both M and H leveled approximately 20% higher than when they were lying down. Over 24-h periods total M and H agreed within the limits of experimental error. Heat storage of the calorimeter contents (MH) was calculated from the accumulated difference between M and H. Day-night cycles observed in MH were partly due to the heat of warming food and water and of cooling excreta (FF). The difference (TB = MH - FF) represented calorimetrically determined changes in heat storage in the animal's body. Day-night cycles in TB were small (less than 1 degree C range in equivalent change in mean body temperature) but agreed well with observed changes in body core (carotid artery) temperatures. It is concluded that day-night changes in heat storage in fixed-temperature environments are small but measurable by calorimetry and that the methods used are applicable for future studies with cyclic environmental temperatures.