Effects of feeding diets composed of corn silage and a corn milling product with and without supplemental lysine and methionine to dairy cows

摘要

Formulating diets with high inclusion rates of afeed that provides necessary nutrients at lower-thanmarketprices for those nutrients should increase incomeover feed costs if the feed is not detrimental toyields of milk and milk components. The objective ofthis study was to determine whether cows fed a dietcomposed of approximately 53% corn silage, 44% cornmilling product (68% dry matter, 21% crude protein,37% neutral detergent fiber, and 9% starch) and 3%minerals (CMP) would have similar productivity ascows fed a control diet of predominantly corn silage,alfalfa silage, corn grain, and soybean meal. Based onthe National Research Council (2001) dairy model, theCMP diet was inadequate in metabolizable methionineand extremely low in metabolizable lysine. A thirdtreatment (CMP+AA) was the same as the CMP dietbut was supplemented with rumen-protected lysineand methionine. Twenty-one Holstein cows were usedin a replicated Latin square (28-d periods) design toevaluate production responses to the 3 diets. Diets wereformulated to contain the same concentration of netenergy for lactation and metabolizable protein (MP)based on the National Research Council model, butdiets with CMP contained more neutral detergent fiber(38.3 vs. 31.4%) and less starch (21.6 vs. 30.5%) thanthe control diet. Lysine as a percent of MP was 6.5,6.0, and 6.8 for the control, CMP, and CMP+AA diets,respectively, and methionine was 1.8, 1.8, and 2.3% ofMP, respectively. Dry matter intake was not affectedby diet (24.3 kg/d), but milk yield was lower for cowsfed either CMP diet than for those fed control (36.0 vs38.1 kg/d). Milk fat concentrations were normal andnot affected by diet (3.7%). Milk protein concentrationwas greater for cows fed CMP+AA than for cows fedthe other 2 treatments (3.19 vs. 3.11%); however, milkprotein yield was greatest for cows fed the conventionaldiet. The concentration of methionine in plasma wassignificantly greater for cows fed CMP+AA than forcows fed the other diets. Plasma lysine concentrationswere greater for cows fed the conventional diet thanfor those fed the other 2 diets. Plasma concentrationsof several essential AA were lower for cows fed eitherCMP diet. Based on calculated energy balance, dietscontained similar concentrations of net energy forlactation, but cows fed CMP diets partitioned moreenergy toward body energy reserves than did controlcows, perhaps because supply of specific AA limitedmilk synthesis.