Effect of post-ruminal infusion of glutamine on plasma amino acids, milk yield and composition in lactating dairy cows

The objectives of this study were to examine the effect of supplying post-ruminal L-glutamine in mid-lactation Holstein dairy cows on plasma amino acid profile, dry matter intake, milk yield and milk composition. The experiment was designed as a 4 x 4 Latin square with four 2-wk periods. Cows were continuously infused post-ruminally with graded levels of L-glutamine (L-Gln) for 5 consecutive days during the second week of each period. During the last 24 h of the infusion, blood plasma was collected every 6 h for the determination of plasma amino acid concentrations. Plasma Gin concentration increased (P < 0.05) with increasing L-Gln daily infusions. Infusion of 0, 100, 200, and 300 g d(-1) resulted in blood plasma Gin concentrations of 289.5, 299.2, 356.4 and 386.2 mu mol L-1, respectively. The level of Gin infusion also resulted in a decrease in the blood plasma concentration of phenylalanine, but the concentrations of all other amino acids were not affected. The administration of Gin did not affect dry matter intake, milk yield and milk composition.