Response to Abomasal Infusion of Methionine of Weaned Dairy Calves Fed a Complete Pelleted Starter Ration Based on By-Product Feeds

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Abstract
Three abomasal infusion trials were made to determine the 1st-limiting amino acid for N retention of postweaned Holstein bull calves fed a starter ration based on cereal by-product feeds. Ration ingredients contributed the following percentages of total amino acids: wheat middlings 38, brewer''s grains 24, hominy feed 21, oat hulls 10, distiller''s grains 6 and molasses 1. Dry matter of the pelleted ration contained 13-14% crude protein and 0.23-0.26% S. Each trial was a replicated 4 .times. 4 Latin square with 9-day periods. Calves were weaned at 4 wk and infusions initiated at 5-6 wk of age. Abomasal infusion of the 10 essential amino acids, an isonitrogenous quantity of an equimolar mixture of alanine, asparagine, glutamate glycine and serine, or an isocaloric quantity of glucose indicated that essential amino acid(s) rather than nonspecific N or energy was limiting protein synthesis. Quadratic responses in urine N excretion and retained N occurred when 0.03, 0.06 and 1.2 g L-methionine/kg starter ration were infused. Greatest responses occurred with 0.6 g methionine, which increased retained N 11 and 19% and decreased urine N 7 and 10%. The relationship between infused methionine and plasma methionine was linear. Infusions in all trials had no effect on digestibility of energy and N.