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Urea for Lactating Dairy Cattle. IV. Effect of Urea versus No Urea in the Concentrate on Production Performance in a High-Producing Herd^{1, 2,}

Department of Animal Sciences, University of New Hampshire, Durham

ABSTRACT

A herd of 56 purebred Holstein cows of high milk-producing ability was divided at random into two groups. One group was fed a premium commercial concentrate during the 18-month experimental period. The other group was fed a similar concentrate mixture in which urea nitrogen replaced plant protein nitrogen to the extent of 3.9 percentage units of equivalent crude protein. All cows were individually fed hay and corn silage, both high quality, to appetite.

Milk production (305-day, mature equivalent basis) for the urea and control groups was 8,028 and 8,059 kg, respectively. Corresponding milk fat production on the same basis was 299 and 308 kg. None of these differences were significant at the 10% level of probability. Concentrate to fat-corrected-milk ratio, as well as percentage solids-not-fat, were the same for both groups.

Mean conception rates in the urea and control groups were 1.6 and 1.9 services per conception, respectively. The proportions of cows requiring one, two or more services for conception were not statistically different (P > .10).

Some evidence was found to support the general recommendation that changes in a lactating cow's ration be made gradually over a period of about two weeks.

¹ Published with the approval of the Director of the New Hampshire Agricultural Experiment Station as Scientific Contribution no. 432.

² This research was partially supported by a grant from Agway, Inc., Syracuse, New York.

³ Statistician, Agricultural Experiment Station.