Effect of permanent access to operant heating on energy balance of growing pigs

Early-weaned littermate piglets were acclimated to cold for 3 wk and then housed for 6 wk at a room temperature of 10 degrees C in individual cages. Half the littermates (OP) could switch on a heater and thus adjust temperature within a cage; the other half (CP) had access to a source of light only. Food was available ad libitum. It was found that when the room temperature was 10 degrees C OP maintained cage temperature at 17.3 degrees C, whereas that of CP was at 10.4 degrees C (P less than 0.001); rectal temperature of OP was 0.4 degree C (P less than 0.01), and locomotor activity 19.9% (P less than 0.001) higher than in CP. Oxygen consumption measured at 25 degrees C was 12.5% lower (P less than 0.05) in OP than CP, but did not differ when measured at 10 degrees C. There were no differences in food intake and growth rate, but the food conversion ratio was improved by 10.9% (P less than 0.01) in OP in comparison with CP. By the end of the experiment CP had shorter bodies, tails and snouts and smaller heads and ears than CP. No difference in distribution of tissues, size of internal organs, or dry matter and energy content in tissues was observed between the groups. The role of autonomic vs. behavioral thermoregulation in maintaining a mammal's energy balance and thermal homeostasis is discussed.