Effect of Grain Level and Protein Content of the Grain for Grazing Cows on Milk Composition and Yield, and Certain Blood and Rumen Constituents

Abstract

Two concentrate mixtures, containing 8.3 and 22.6% crude protein, were fed at 1kg per 1.75, 3.5, and 7.0kg of milk produced during standardization to 48 lactating Holstein cows grazing medium-quality Blue-grass pasture. Milk was sampled for composition analyses at ten-day intervals. Jugular blood samples were taken for determination of serum protein and protein fractions, and rumen contents sampled for VFA analyses.Milk yields were significantly related to levels of dietary protein and grain. Per cent SNF, protein, and lactose-mineral in the milk increased as level of feeding increased, but were not affected by ration protein. No interaction between dietary protein and energy was noted for milk constituents. The high-grain ration resulted in depressed milk fat and increased rumen propionate. Neither rumen acetate, butyrate, nor any of the blood protein fractions were significantly affected by grain level. The high-protein ration resulted in higher concentrations of total VFA, acetate, propionate, and butyrate in rumen fluid; and in higher albumin and NPN and lower alpha globulin in blood serum.