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

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Abstract
Two concentrate mixtures, containing 8.3 and 22.6% crude protein, were fed at 1 kg per 1.75, 3.5 and 7.0 kg of milk produced during standardization to 48 lactating Holstein cows grazing medium-quality bluegrass pasture. Milk was sampled for composition analyses at 10-day intervals. Milk yields significantly increased as protein and grain levels increased. Percent SNF [solids-non-fat], protein and lactose-mineral in the milk increased as grain level increased, but were not affected by ration protein. The high grain ration resulted in depressed milk fat, and increased rumen propionate. The high protein ration resulted in higher concentrations of total VFA [volatile fatty acid], acetate, propionate, and butyrate in rumen fluid, and in higher albumin and NPN [non-protein nitrogen] and lower [alpha] globulin in blood serum.