Influence of Dietary Energy and Protein on Yield and Composition of Milk from Cows Fed Methionine Hydroxy Analog

Abstract

In three trials in consecutive years, 45, 59, and 63 lactating Holstein cows were fed grain mixtures containing either 0 or .25% methionine hydroxy analog with or without protein supplement. In Trial 1, diets were approximately 40% concentrate, and dietary protein averaged 13.2 and 15.8% (dry). Ration dry matter consisted of either 40 or 60% concentrate, and dietary protein averaged 13.5 or 17.3% in Trial 2 whereas concentrate was maintained at 60% of dry matter in Trial 3 with dietary protein at either 13.0, 15.0, or 17.5%. In Trial 1, milk yield or composition did not differ with methionine analog or protein supplementation. Protein supplementation increased milk yield on the 60% concentrate diets in Trial 2, and methionine analog increased milk fat percentage on the 60% concentrate diets. Cows fed 17.5% crude protein in Trial 3 produced more milk than those fed the two lower protein diets. Methionine analog increased milk fat percentage, and this increase was consistent at each percentage of dietary protein. Data from 179 lactations were combined and analyzed for response in milk yield and composition to methionine analog included at either 0 or .25 to .30% of grain mixtures in 60% concentrate diets. Cows fed methionine analog produced milk higher in fat content and yielded more total fat and fat-corrected milk than controls. © 1983, American Dairy Science Association. All rights reserved.