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 × 2 factorial approach the productive and metabolic response of 24 multiparous Brown Swiss cows fed rations calculated to be deficient in leucine (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 matter basis the rations consisted of 29% grass silage, 20% maize silage, 6% hay, and 45% concentrate.Blood plasma amino acid data confirmed the intended difference in metabolic supply of leucine and methionine keeping a low variation in the plasma levels of the other essential amino acids, particularly 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 were significantly reduced relative to initial level without additional methionine.Nutrient digestibility and nitrogen balance remained widely unchanged by the supplementations.Except of plasma aspartate amino transferase, cholesterol, creatinine and ornithine, which responded to methionine, hormones, enzyme activities as well as plasma, urine and milk metabolites were not systematically influenced by leucine and methionine supply.The present results gave clearer indications for a deficiency in methionine than in leucine. amino acids / dairy cow / requirements / leucine / methionineRésumé -Effets de l'apport de leucine et méthionine chez des vaches en début de lactation recevant des rations ensilage-concentré à déficit calculé en leucine et méthionine.Vingt-quatre vaches laitières multipares Brown Swiss ont été affouragées avec des rations calculées pour être déficientes en leucine (0,9 fois du besoin) et méthionine (0,8 fois).Les effets d'une supplémentation de l'un ou des deux acides aminés sur la production et le métabolisme de ces vaches ont été examinés à l'aide d'une approche factorielle 2 × 2. En matière sèche, les rations étaient composées de 29 % d'ensilage d'herbe, 20 % d'ensilage de maïs, 6 % de foin et 45 % de concentrés.Comme