Manipulating energy metabolism in sheep exposed to cold.

The effects of dietary fats level (0 and 7% tallow) and monensin (0 and 33 mg/kg of diet) were investigated in lambs at ambient temperatures of -11.9 and 12.9 C. Twenty-four nonfistulated and 16 fistulated lambs with an average weight of 73 kg and fleece length of 8 cm were randomly assigned to each fat and monensin level (6 nonfistulated and 4 fistulated lambs per treatment) in a 2 x 2 factorial arrangement of diets. There were no main treatment effects on organic matter or crude protein digestibility, though ether extract digestibility was higher on the high-fat diets (P less than 0.001) and at 12.9 C (P less than 0.05). Fat decreased (P less than 0.05) molar proportions of ruminal acetate and increased propionate. Monensin increased (P less than 0.001) propionate and decreased (P less than 0.05) butyrate. Propionate was 26% higher at -11.9 C. Respiration rate tended to be higher on the high-fat diets and was doubled (P less than 0.001) and the warm temperature (12.9 C). There were no main treatment effects on rectal temperature. Heart rate was increased (P less than 0.05) by 12% on the high-fat diets. Cold temperature exposure significantly increased free fatty acids, thyroxine, protein-bound iodine and phosphorus, and decreased plasma urea nitrogen in jugular blood. Free fatty acid and triglyceride concentrations were higher (P less than 0.05) on the high-fat diets. There were no main treatment effects on either glucose or calcium levels. These results show that dietary fat level and monensin did not consistently influence the sensitivity of full-fleeced lambs to the effects of cold-temperature exposure.