Effects of urea and soybean meal supplementation on rates of plasma leucine turnover and protein synthesis in sheep fed concentrate-based diets

Abstract

The isotope dilution method of [1-13C]leucine (Leu) and open-circuit calorimetry were used to determine the effects of urea and soybean meal (SBM) supplementation on rates of plasma Leu turnover and whole body protein synthesis (WBPS) in sheep fed concentrate-based diets. The experiment was performed in a replicated 3×3 Latin square design. The control diet (Control diet) consisted of timothy hay and ground corn. The urea supplemented diet (Urea diet) was supplemented with 3.1% urea of the Control diet. The SBM diet was similar to nitrogen and ME contents to the Urea diet by replacing 40% ground corn of the Control diet to the SBM. Plasma urea concentration was higher (P<0.05) for the SBM and Urea diets compared with the Control diet, but plasma ammonia concentration remained similar for all diets. Plasma free amino acid concentration also remained unchanged between the diets, except for plasma glycine concentration. Plasma Leu turnover rate and WBPS did not differ between the diets, but they were numerically higher for the SBM diet compared with the Control and Urea diets. These results suggest that in sheep, urea and SBM supplementation influence little on plasma Leu and protein metabolism, when concentrate-based diets are given.