Factors affecting the responses in milk yield and milk composition of dairy cows to postruminal supplies of methionine and lysine : a review

Abstract

The purpose of this review was to determine the responses of dairy cows to postruminal supplies of methionine and lysine and their factors of variation. Published data (121) related to postruminal (AA infusions and protected AA) Met and/or Lys supplies and their effects on milk yield and milk composition were analysed. Broadly, postruminal AA supply increases milk protein and casein content. This increase is much higher when Met and Lys are associated (1.1 g/kg) than when they are not (0.4 g/kg). When given together, the response to these AA is greater with high maize diets (1.1 g/kg) than with low maize diets (0.7 g/kg). With high maize diets, the response is lower (0.9 g/kg) with low nitrogen rations than with high nitrogen rations (1.3 g/kg). With the latter rations the response increases proportionally with the amount of lysine (0.05 g/kg per gram of additional lysine). With this type of diet, postruminal Lys and Met supply during the first 9 weeks of lactation significantly increase the milk yield (0.7 kg/d). Finally, compared to responses obtained with casein infusions (all AA included), Met and Lys explain alone 21 % of milk, 58 % of protein yield and nearly 100 % of protein content responses.