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Influence of Dietary Nitrogen Source, Concentrate Level and Biuret Level in Sheep on the Adaptation of Rumen Microorganisms to Biuret as a Nonprotein Nitrogen Source^{1, 2}

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

Four trials were conducted to study the ability of rumen microorganisms to adapt to biuret as a source of nitrogen when the diet contained various levels of readily fermentable carbohydrate. Biuretolytic activity of the rumen contents was determined in vitro by measuring biuret disappearance and NH₃ release. Sheep adapted rapidly to biuret when fed diets containing low to moderate levels of starch, reaching maximum biuretolytic activity within the first 10 days of feeding. This rate of adaptation is faster than that observed with all-roughage diets. No biuretolytic activity was noted for animals fed cottonseed meal or urea as the supplemental nitrogen source. The rate of biuret adaptation was influenced by 1) the level of biuret fed and 2) the level of starch in the diet. When biuret supplied less than 15% of the digestible nitrogen requirement, little or no biuretolytic activity was observed. The rate of biuret adaptation and extent of hydrolysis generally favored those diets containing 20% ground corn compared to diets containing higher levels or no corn at all. When the biuret was removed from the diet, biuretolytic activity was decreased considerably within 2 days and completely lost within 4 days. Performance and digestibility data indicated that biuret was comparable to cottonseed meal and urea as a nitrogen source when the diet contained 60% ground corn.

KEY WORDS: • biuret • rumen • NPN • microbial adaptation

¹ Journal Article 2607 of the Agricultural Experiment Station, Oklahoma State University, Stillwater, Okla, 74074.

² A preliminary report of portions of this research was presented at the Annual Meeting of the American Society of Animal Science, August 1972, at Blacksburg, Virginia, E. T. Clemens and R. R. Johnson, Adaptation-deadaptation to biuret by sheep fed high concentrate rations. J. Anim. Sci. 35: 227 (abstr.).

Manuscript received 18 December 1972.