Effect of Nitrogen Fertilization or Urea Supplementation upon the Digestibility of Grass Hays

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Abstract
Two total collection digestion trials were carried out using dairy heifers to determine the effect of N-supplementation upon feeding value of 2nd-cutting orchard-grass and bromegrass hays. Second-cutting alfalfa hay was used as the comparison roughage. The N was applied as fertilizer just after the 1st-cutting or applied as urea in a spray on the hay just prior to feeding. The addition of 200 lb. of N/A to orchardgrass or bromegrass increased the crude protein (CP), TDN, (total digestible nutrients) and gross energy above that hay fertilized with no more than 25 lb. N/A. This high rate of application significantly increased the apparent digestion coefficients of protein and energy above those of the low-N hay rations. The apparent digestion coefficients of fiber of the grasses were significantly higher than those of the alfalfa hays. Urea was added to low-N hay (15 g/lb. of hay) to make the protein equivalent of high-N hay. The apparent digestion coefficients of protein and fiber and the TDN of the low-N-plus-urea ration were not only significantly greater than the low-N hay but were significantly greater than the high-N and alfalfa hays.
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