Influence of Dietary Protein Concentration on Milk Production by Dairy Cattle during Early Lactation

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Abstract
In a 3 .times. 2 factorial experiment 75 Holstein cows in 1st, 2nd or 3rd lactation were fed rations containing either 12.2% or 16.2% crude protein in total ration dry matter. On the average, 26% of dry matter intake was from corn silage, 22% from alfalfa-grass hay, and 52% from a grain mix. Protein was controlled by feeding a 13.7% crude protein grain mix with 1.4% urea for the 12% ration and a 19.8% crude protein grain mix with natural protein for the 16% ration. Average daily milk production (kg/day) for weeks 2-12 of lactation for 12% and 16% rations by lactations were discussed. Dry matter intakes by lactations were .42, 1.18 and 2.05 kg/day higher for cows fed the high protein compared to low protein rations. Milk composition was not influenced by protein treatment. The markedly different response to protein supplementation in milk production between heifers in first lactation and more mature cows is unexplained.