An isotope dilution method using [U-(13)C]glucose injection was applied to determine the effects of dietary energy intake and cold exposure on plasma glucose metabolism in sheep. The sheep were assigned to two dietary treatments and were fed on diets containing either 100% or 160% of ME and both containing 150% of dietary crude protein intake for maintenance. The sheep were exposed from a thermoneutral environment (23 degrees C) to a cold environment (2-4 degrees C) for 5 days. The isotope dilution method was performed on the 18th day in the thermoneutral environment and on the fifth day of cold exposure. Plasma concentrations of glucose and NEFA increased (p < 0.05) during cold exposure for both diets. Plasma glucose pool size remained unchanged (p = 0.67), but plasma glucose turnover rate tended to increase (p = 0.07) with increased energy intake. Both pool size and turnover rate of plasma glucose increased (p = 0.01 and p = 0.0001, respectively) during cold exposure. No significant diet x environment interaction was detected. It is concluded that plasma glucose metabolism was influenced by both dietary energy intake and cold exposure, and plasma glucose metabolism in response to cold exposure was not modified by energy intake in sheep under the conditions (2-4 degrees C on the fifth day) of the present experiment.

SU MMARYDilution of [1-13 C]leucine (Leu) and open-circuit calorimetry were used to determine the effects of diet and cold exposure on rates of plasma Leu turnover, Leu oxidation, and whole body protein synthesis (WBPS) in sheep. The experiment was designed as a crossover design for two 23-day periods. Six adult sheep were assigned to two dietary treatments, medium (Me-diet) and high (Hi-diet) intake, and were fed either 515 or 830 kJ/kg BW 0 . 75 per day of metabolizable energy intake, respectively. The temperature in the chamber was changed from a thermoneutral environment (23 xC) to a cold environment (2-4 xC) for 5 days (the 18th to 23rd day of the experiment). Turnover rate of both plasma Leu and WBPS were greater (P<0 . 01) for the Hi-diet compared with the Me-diet and increased (P<0 . 01) during cold exposure. Leucine oxidation rate was numerically greater (P=0 . 10) for the Hi-diet compared with the Me-diet and increased (P=0 . 03) during cold exposure. No significant dietrenvironment interaction was detected in the rates of plasma Leu turnover, Leu oxidation or WBPS. It is concluded that plasma Leu kinetics and WBPS were influenced by intake level and increased during cold exposure, but the responses to cold exposure were not modified by intake level in sheep under the conditions of the present experiment.