Resting metabolism and thermoregulation in the unrestrained rabbit

Zealand white rabbits at ambient temperatures (T,) of 0, 10, 20, and 30 ’ C. In unrestrained and trained rabbits, values of M were lower than previously reported for restrained rabbits. Calculated heat loss coefficient and lower critical temperature were also lower than previously reported. Rabbits show three postures dependent on the T,. The relaxed/alert posture (at T, = 20 ’ C), the ball posture (at T, = 0 and 10QC), and the spread posture (at T, = 30 ° C). Heat conservation by vasomotor adjustment of the ears was calculated and found to be linear with decreasing T;,. The ability to change posture and state of excitability of the rabbit are important in determining the animal’s metabolic response to ambient temperature. behavior; metabolic rate BECAUSK OF THE INCREASING USE of rabbits in modeling thermoregulatory control systems, we believe it is necessary to determine the resting state of the unrestrained rabbit. Then the role of behavioral thermoregulation in the energy balance of these animals can be evaluated. Recent reports show that rabbits respond to variations in ear temperature (6, 7), ambient temperatures (1, 2, 6, IO), and various core temperature manipulations (1, 3, 8) by changes in vasomotor state and heat production. In each paper, resting oxygen consumption was measured on restrained rabbits unable to make appropriate postural adjustment to ambient temperatures. Metabolic rates were significantly higher than we have obtained from quiet un-restrained rabbits. We designed our experiments to determine resting metab-olism on quiescent animals free to change posture and ob-served steady-state oxygen consumption and vasomotor conditions over the test period. We believe we have a more accurate determination of resting metabolism and obtain a wider thermoneutral zone, and a smaller heat exchange coefficient than have been previously reported (I, 3, 9)