Adaptation of homeostatic thermoregulation: comparison of incubating and non-incubating bantam hens.

Incubating and non-incubating Bantam hens were exposed to identical thoracic skin cooling to study the difference between their physiological responses with regard to thermoregulatory adaptation to incubation. Under resting conditions thoracic skin temperature (Tths) and metabolic heat production (M) were significantly higher in broody than in non-broody hens, indicating a permanently increased conductance of the brood patch. Thoracic skin cooling from 35 to 25 degrees C decreased Tths less in broody than in non-broody hens. In broody hens, these coolings induced a large, immediate increase in M, no constriction of brood patch vasculature, and a decrease in colonic temperature (Tc). This decrease in Tc triggered no further increase in M, but induced vasoconstriction in the feet. The coolings induced a smaller increase in M in the non-broody hens, accompanied by pronounced vasoconstriction, and did not affect Tc and foot temperature, Tf. The effects of more severe thoracic skin cooling (between 25 and 15 degrees C) differed much less between non-broody and broody hens. Vasoconstriction of the brood patch also occurred in the latter. It is concluded that in adaptation to incubation the thoracic skin becomes more sensitive, and its input signal becomes stronger for the control of certain effector systems of thermoregulation, allowing a controlled heat transfer to the eggs.