Effects of diet and cold exposure on rates of plasma leucine turnover and protein synthesis in sheep

Abstract

SUMMARYDilution of [1-13C]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 BW0·75per day of metabolizable energy intake, respectively. The temperature in the chamber was changed from a thermoneutral environment (23°C) to a cold environment (2–4°C) 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 diet×environment 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.