Effects of somatotropin and duodenal infusion of amino acids on nutrient passage to duodenum and performance of dairy cows

Four multiparous Holstein cows were used in a 4 X 4 Latin square to investigate the effects of bST and postruminal infusion of lysine and methionine on ruminal fermentation, flow of nutrients to the small intestine, and animal performance. The treatments were 1) control; 2) control plus 24 g of lysine and 8 g of methionine/d; 3) control plus 25 mg of bST/d; and 4) control plus 25 mg of bST/d plus 24 g of lysine and 8 g of methionine/d. Intakes of DM, OM, CP, starch, NDF, and ADF were similar among treatments. Ruminal characteristics, flow of nutrients to the small intestine, and total tract apparent digestibilities of nutrients were not affected by injection of bST or postruminal infusion of lysine and methionine in this short-term experiment. Milk production, 4% FCM, milk fat percentage and yield, and production of milk CP were increased by administering bST. Postruminal infusion of lysine and methionine did not affect milk production or composition