Effects of Dry or Ensiled Feeds and Protein Percent on Milk Production and Nitrogen Utilization by Lactating Cow

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Abstract
In two 2 .times. 2 factorial experiments, 28 cows in 1st and later lactation and 28 cows in 2nd and later lactation were fed rations containing either dry (low N solubility) or ensiled (high N solubility) feeds with low (14%) or high (16%) concentrations of crude protein. Rations were formulated with hay or hay crop silage and dry shelled corn or high moisture shelled corn in a 50:50 ratio (trial 1) or 40:60 ratio (trial 2) of forage to concentrate in the dry matter. Soybean meal was used to alter the protein content. Protein percent had no effect on milk yield or milk composition in either trial, although N digestibility was greater on high protein diets. Solids-corrected milk yield and milk fat percent were lower when N solubility of the ration was increased in trial 2 but not in trial 1. Analysis of N balance data indicated higher conversion of N of feed to N of milk for low solubility diets in trial 1 and high solubility diets in trial 2.