Effect of dietary protein on high-producing dairy cows in early lactation

Thirty Holstein cows capable of producing at least 30 kg of milk per day were assigned to one of three completely mixed rations containing corn silage, chopped alfalfa hay, and concentrate mixture. These rations differed only in crude protein content (12.7, 16.3, or 19.3% dry matter). All cows were fed their assigned ration continuously for 90 days beginning on the 4th day post-partum. Differences in average 4% fat-corrected milk, persistency of production, change in body weight, milk protein content, blood ammonia, plasma albumen, and rumen pH between groups of cows were not significant. Cows fed the higher protein rations had more 4% fat-corrected milk and feed intake throughout the trial. Groups of cows differed in average rumen ammonia and urea in blood plasma in relation to the protein content of the ration. Income above cost of feeds for the 90-day trial was greatest for the group fed the 16.3% crude protein ration and lowest for the group fed the 19.3% crude protein ration.