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Evaluation of Beef Cattle Range Supplements Containing Urea and Biuret^1,2,

Agricultural Experiment Station, Stillwater 74074

Abstract

Two winter trials were conducted with 304 lactating range cows on dry grass to evaluate non-protein-nitrogen (NPN) in 30% protein supplements containing biuret (pure and feed grade), urea and extruded grain-urea. The NPN sources contributed one-half of the supplemental nitrogen with natural 15 and 30% protein supplements serving as negative and positive controls.

Winter weight loss of cows was greater (P.02) on the negative than on the positive control in both trials. The apparent utilization of all NPN sources was low and the utilization of urea and extruded grain-urea was less than pure or feed grade biuret. Rumen biuretolytic activity was apparent within 6 days and reached and maintained a high level of activity 20 days after the initiation of feeding biuret, even with intermittent supplementation. Apparent value of NPN supplements was slightly improved with 40% dehydrated alfalfa but not with methio-nine-hydroxy-analogue (MHA). Palatability of supplements was lowered by urea and especially by MHA and extruded grain-urea.

In a third trial with yearling heifers fed prairie hay, gains were similar on natural protein and supplements containing urea or extruded grain-urea to provide one-half of the nitrogen. When the heifers were fed the same supplements but low quality winter harvested range grass, NPN utilization appeared to be low.

¹ Journal Article 2814 of the Agricultural Experiment Station, Oklahoma State University, Stillwater.

² The authors express appreciation to R. K. Johnson and J. V. Whiteman for assistance in statistical analysis and Bill Sharp and Ray Heldermon for care of experimental animals. Grateful acknowledgement is also expressed to Dow Chemical, Midland, Michigan, for feed grade biuret and partial financial support; E. I. duPont de Nemours and Company, Wilmington, Delaware, for a source of methionine-hydroxy-analogue and partial financial support; Far-Mar-Co., Inc., Hutchinson, Kansas, for a source of extruded urea-grain and partial financial support; Nipak, Pryor, Oklahoma for urea and pure biuret, and Triple "F" Feeds, Des Moines, Iowa for a source of extruded urea-grain.

³ Presently District Extension Livestock Specialist, Panhandle Experiment Station, Scottsbluff, Nebraska.

⁴ Presently Head, Animal Science Department, University of Tennessee, Knoxville 37900

⁵ Department of Animal Sciences and Industry, Oklahoma State University, Stillwater 74074

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