Heat dissipation biorhythms of laboratory animals

Body heat dissipation rates were determined in greyhound and beagle dogs, the rabbit, and the rat. Each group of animals was confined in standard cages in a controlled environment room maintained under conditions of 24 degrees C, 50% relative humidity, and fixed ventilation rats. Food and water were available ad libitum. Heat dissipation rates were determined for each group and normalized to an individual animal basis. The ratio of actual heat dissipation to standard metabolic rate, the metabolic heat ratio, was 2.01+/-0.18 for the greyhound, 1.98+/-0.03 for the beagle, 2.66+/-0.20 for the rabbit, and 1.95+/-0.13 for the rat. For each species, the ratio displayed a 24-hour cyclic pattern in which four contiguous maximum values differed significantly from four contiguous minimum values. The ratios of maximum values to minimum values were between 1.54 and 1.75.