Evaluation of Corn Distillers Grains and Ruminally Protected Methionine and Lysine for Lactating Dairy Cows

Twelve multiparous Holstein cows averaging 57 d postpartum at the start of the experiment were utilized in a replicated 4 x 4 Latin square design. Diets were 1) Soybean meal (SBM) without rumen protected Met and Lys (RPML), 2) SBM with RPML, 3) Corn distillers grain (CD G) without RPML, 4) COG with RPML. Dry matter intakes were lower for the SBM diets than the COG diets (28.7, 27.7, 29.4, 30.0 kg/d). Milk yield was improved with the COG diets (34.3, 34.0, 35.3, 36.7 kg/d) especially when COG diet was supplemented with RPML. Milk protein yield and percentage were improved by RPML. Milk fat yield and percentage were unaffected by diet. The only milk crude protein component significantly affected was nonprotein nitrogen which was lower in milk for cows fed COG. Other milk protein components were unaffected by dietary protein source or RPML. Lysine, methionine, and phenylalanine were indicated as the most limiting amino acids for all diets when using amino acid extraction efficiency and transfer efficiency which indicate amino acid limitations. Concentrations of total ruminal volatile fatty acids (V FA) were highest for the SBM, however, molar proportions of individual VFA and concentrations of ruminal ammonia and serum urea were similar for all diets. Supplementing COG with RPML increased milk yield, as well as, milk protein yield and percentage primarily because the COG diet was deficient in lysine