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Urea Utilization in Protein Supplements for Cattle Consuming Poor Quality Roughages on the Range

Oklahoma Agricultural Experiment Station, Stillwater ^,2

Abstract

One-hundred-ninety pregnant and lactating grade Angus cows were alowed to graze dead range grasses during the winter season. In addition, one-half were fed a 21% crude protein equivalent supplement containing 4.0% urea while the remaining ones were fed a supplement in which solvent-extracted cottonseed meal was fed at a level isonitrogenous with the urea. Cows fed the urea-containing supplement lost more weight than those fed cottonseed meal. Birth and weaning weights of the calves were not affected significantly by treatment, but trends apparently favored those fed cottonseed meal. Ruminal fluid ammonia levels were significantly higher in the urea-fed animals until 300 minutes after feeding; the level then dropped to one comparable to that found in those fed cottonseed meal.

In a second trial, various NFE:N ratios in urea-containing supplements were fed when cottonseed hulls were the roughage source. The NFE:N ratios varied from 11 to 55:1, in equal spacing, and it was found that nitrogen retention improved in a manner not differing from linearity up to a ratio of 28:1 and that no further improvement resulted.

¹ Department of Animal Sciences and Industry.

² Approved by the Director.