Lactational and metabolic effects in cows of lysine and methionine added to a ration deficient according to the INRA method

The effects of adding lysine and/or methionine to a ration of calculated de ficiency in these amino acids of 10% and 20%, respectively, were studied in 24 Brown Swiss cows. The mixed rations (27% grass silage, 19% maize silage , 5% hay and 49% concentrate on DM basis) contained 14.5% CP on average. Ly sine supply was selectively elevated by adding fish meal in exchange for ot her concentrate ingredients. Methionine was supplied in a rumen-protected f orm. Milk protein content was elevated whereas fat amount decreased by addi ng both amino acids. Lactose content increased without additional lysine fr om fish meal. Live weight, milk yield, milk fat content and protein amount remained unaffected by any variation of amino acids supply. Also nutrient d igestibility and nitrogen balance were not changed by the treatments. Blood plasma concentrations confirmed the assumed variation in metabolic lysine and, less clear, methionine supply. Effects on plasma concentrations of oth er amino acids were relatively small. Most plasma hormones and enzymes, and metabolites in plasma. urine and milk did not respond to the variation in amino acid supply. Lysine addition via fish meal increased aspartate amino transferase and decreased urinary allantoin concentration. Additional methi onine elevated plasma ornithine. Overall lysine and methionine appear to ha ve been only marginally deficient in the unsupplemented ration fed for 3 we eks despite the deficiency of 10% to 20% as calculated by the I.N.R.A. meth od.