Abstract:

【Objective】 This trial was designed to study the effects of dietary lysine to methionine ratio on growth performance, nutrient digestibility and nitrogen metabolism in weaned calves. 【Method】 Twenty four weaned calves were randomly allocated into four treatments either fed a control diet containing 14.76%DM CP or one of the three trial diets containing 12.02% DM CP and the dietary lysine/ methionine ratios were 2.5﹕1, 3.0﹕1 or 3.5﹕1, respectively, for 8 weeks. The calves were weighed and blood samples were collected on the initial and final day of the experiment. Four calves were selected from each group and metabolism trials were conducted from the third week of the feeding experiment by total feces collection method. 【Result】 The results indicated that the gain of calves in group 3.0﹕1 was higher than that of calves in other groups numerically (P＞0.05). Serum concentrations of urea nitrogen in calves fed test diets was lower than that in the control (P＜0.01). The concentrations of free amino acid in serum were lower (except methionine) in calves fed test diets than those in control group (P＞0.05). No difference was observed in serum concentration of urea nitrogen and free amino acids (except arginine and valine) among test groups. The utilization and apparent biological value of nitrogen in group 3.0﹕1 and group 3.5﹕1 were higher than group 2.5﹕1 and control group numerically (P＞0.05). 【Conclusion】 The gain of calves fed diet addition of RPLys and RPMet with a crude protein level of 12.02% was higher than that fed diet with a crude protein level of 14.67%. The ratio of lysine and methionine at 3.0﹕1 in diets could enhance growth performance and utilization of nitrogen in weaned calves.

Key words: calf, amino acid ratio, growth performance, digestibility and metabolism