Influence of abomasal infusion of high levels of lysine or methionine, or both, on ruminal fermentation, eating behavior, and performance of lactating dairy cows

Four multiparous late-lactation Holstein cows were fed a basal ration desig ned to be co-limiting in intestinally absorbable supplies of methionine and lysine. Cows were supplemented with no amino acids, lysine by abomasal inf usion to 140% of the calculated intestinally absorbable requirement, methio nine by abomasal infusion to 140% of requirement, or both amino acids in a 4 x 4 Latin square design with 28-d periods. Unsupplemented cows consumed 2 3.8 kg/d of dry matter and produced 36.9 kg/d of milk containing 3.70% fat, 3.22% protein, and 4.82% lactose. Cows ate less dry matter and produced le ss milk and milk lactose, and tended (P = .06 or .08) to produce less milk protein when abomasally infused with methionine alone or together with lysi ne. Infusion of lysine alone resulted in production values numerically betw een those of unsupplemented cows and those cows supplemented with methionin e alone or together with lysine. Evaluation of the results with two metabol ic models of dairy cows indicated that performance of unsupplemented cows m ay have been limited by delivery of metabolizable or digestible protein, or intestinally absorbable lysine, isoleucine, or histidine, depending on the metabolic model used to evaluate animal performance. Regardless, results a re consistent with those using non-ruminant species, which have shown that imbalanced profiles of intestinally absorbable amino acids are associated w ith reduced dry matter intake and animal performance. Results also show tha t negative effects on performance of lactating dairy cows can occur if meth ionine is supplied at levels substantially in excess of calculated intestin ally absorbable requirements, either alone or together with lysine.