Effects of supplying leucine and methionine to early-lactating cows fed silage-concentrate based diets with a calculated deficiency in leucine and methionine

In a 2 x 2 factorial approach the productive and metabolic response of 24 m ultiparous Brown Swiss cows fed rations calculated to be deficient in leuci ne (0.9-fold of requirements) and methionine (0.8-fold) to supplementation either of one or both of these amino acids were investigated. On a dry matt er basis the rations consisted of 29% grass silage, 20% maize silage, 6% ha y, and 45% concentrate. Blood plasma amino acid data confirmed the intended difference in metabolic supply of leucine and methionine keeping a low var iation in the plasma levels of the other essential amino acids, particularl y lysine. Live weight, milk yield as well as content and amount of milk fat were not affected by the treatments. Content and amount of milk protein we re significantly reduced relative to initial level without additional methi onine. Nutrient digestibility and nitrogen balance remained widely unchange d by the supplementations. Except of plasma aspartate amino transferase, ch olesterol, creatinine and ornithine, which responded to methionine, hormone s, enzyme activities as well as plasma, urine and milk metabolites were not systematically influenced by leucine and methionine supply. The present re sults gave clearer indications for a deficiency in methionine than in leuci ne.