Effect of cold exposure on profiles of metabolic and endocrine responses and on responses to feeding and arginine injection in sheep.

The effect of cold exposure (0 degrees C) on profiles of total heat production (HP), energy metabolism, and blood metabolite and hormone concentrations were measured in nine shorn Suffolk rams. Blood metabolite and hormone responses to feeding and to i.v. arginine injection (.625 mmol/kg BW) and postprandial changes in HP were also measured. Heat production was greater (P < .05) during cold exposure than in the thermoneutral environment due to enhanced (P < .05) nonprotein oxidation. Protein oxidation and nitrogen balance remained unchanged during cold exposure. Plasma glucagon concentrations increased (P < .05) during the initial period of cold exposure. Heat production increased (P < .01) after the initiation of feeding in both environments. Heat production returned gradually to prefeeding values in the thermoneutral environment, but it remained close to the higher levels during cold exposure. Plasma insulin and glucagon concentrations increased (P < .05), and plasma growth hormone concentrations decreased (P < .10) after the initiation of feeding in both environments. Plasma glucagon responses to feeding (P < .05) and plasma insulin responses to arginine injection (P < .01) were reduced by cold exposure. We suggest that 1) enhanced HP in sheep exposed to cold is maintained by enhanced nonprotein oxidation and 2) endocrine responses to stimulants are influenced by cold exposure, even though profiles after cold exposure change little.