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Urea for Lactating Dairy Cattle. III. Nutritive Value of Rations of Corn Silage Plus Concentrate Containing Various Levels of Urea^{1, 2,}

Departments of Animal Sciences and Analytical Services Agricultural Experiment Station, University of New Hampshire, Durham

ABSTRACT

Four mature Holstein cows were used simultaneously in a 4 x 4 Latin-square design (balanced for residual effects) to evaluate rations containing various proportions of concentrate urea. Corn silage was fed ad libitum as the sole forage. All concentrates were isocaloric and isonitrogenous, each containing the same amounts of every ingredient except soybean oil meal, urea, and hominy.

Ration intake and ration utilization, except for body nitrogen retention, were not affected by the substitution of as much as 300 g of urea per cow daily for equivalent plant protein nitrogen in high-quality concentrates fed with free-choice corn silage to dairy cows. Inclusion of urea in the ration significantly reduced nitrogen retention. Rumen fluid organic acids at intervals before and after feeding were not significantly affected by urea treatment. Inclusion of urea in the ration significantly increased rumen ammonia concentrations during the first hour after feeding, but the ammonia apparently was metabolized satisfactorily by the cows. It was concluded that high-quality concentrate mixtures containing as much as 2.5% urea (by weight) may be fed at relatively high levels with corn silage to lactating dairy cattle with no significant adverse effect on ration utilization.

¹ Published with the approval of the Director of the New Hampshire Agricultural Experiment Station as Scientific Contribution no. 426.

² The research was partially supported by a grant from the E. I. DuPont de Nemours and Company, Wilmington, Delaware.

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