Effects of ruminally protected amino acids on milk yield and blood components of early lactating dairy cows fed grass silage-based diet

Abstract

Two experiments were conducted to examine the effects of ruminally protected methionine (RPM) and lysine (RPL) on milk yield, milk composition and blood components for early lactating dairy cows fed the diet grass silage based. In experiment 1, sixteen multiparous cows were fed a total mixed ration with or without RPM (30g/d of DL-methionine) for sixteen weeks after parturition. In experiment 2, fourteen multiparous cows were fed a total mixed ration with or without RPM (15g/d of DL-methione) and RPL (20g/d of L-lysine) for twelve weeks after parturition. DM intake and milk yields were not affected by treatment in experiment 1 and 2. However, amino acid supplementations increased milk protein contents by 0.20% unit (2.87% vs. 3.07% ; P<0.02) from 3 to 8 weeks after parturition in experiment 1, and by 0.20% unit (2.80% vs. 3.00% ; P<0.21) from 3 to 12 weeks after parturition in experiment 2. Addition of RPM increased serum concentration of methionine in experiment 1 and 2 (P<0.01). But, addition of RPL did not affect serum concentrations of lysine, in experiment 2. These results indicated that RPM supplied the amino acid limiting milk protein synthesis, and increased milk protein contents when cows were fed grass silage-based diets.