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Studies of the Adaptation Phenomenon by Lambs Fed Urea as the Sole Nitrogen Source: Digestibility and Nutrient Balance

Virginia Polytechnic Institute and State University^{,2, 3, 4,}, Blacksburg 24061

Abstract

When urea is first introduced into the diet of ruminants performance is usually less than for animals fed only preformed protein. The lower performance of fattening cattle fed urea as a source of supplemental nitrogen may be due to the lower performance during the first part of the period (Meiske and Goodrich, 1966; Perry et al., 1967). The adaptation phenomenon has been shown to occur in dairy cows fed virtually 100% non-protein nitrogen (Virtanen, 1966). In lambs fed semi-purified diets maximum urea nitrogen utilization occurred after 35 days (Welch et al., 1957). Retention of absorbed nitrogen increased by about 0.2 to 0.3 percentage unit per day up to 50 days (Smith et al., 1960; McLaren et al., 1965) in lambs fed diets containing 1.7% nitrogen, two-thirds of which was supplied by urea.

In experiments with cattle fed natural diets high in crude protein content no evidence of adaptation to urea feeding was observed (Johnson and McClure, 1964; Oltjen et al., 1969).

¹ Present address: Department of Animal Sciences. University of Kentucky, Lexington 40506.

² The research was supported in part by a grant-in-aid from W. R. Grace and Co., Research Division, Clarksville, Maryland.

³ The assistance of C. Y. Kramer in the statistical analyses is gratefully acknowledged.

^₄ Department of Animal Science.