Nitrogen Utilization by Lambs Fed Purified Rations Containing Urea, Gelatin, Casein, Blood Fibrin, and Soybean Protein

Publisher Website
Google Scholar
Abstract
Lambs were fed purified rations supplemented with either urea, gelatin, casein, soybean protein, or bovine blood fibrin to supply nearly 100% of the total nitrogen of the ration. A metabolic nitrogen level of 2.39 mg of nitrogen per gram of dry matter intake or 7.17 mg of nitrogen per gram of dry matter excreted was determined for lambs fed a nitrogen-free ration. Metabolic nitrogen expressed on the basis of excreted dry matter rather than on dry matter intake gave more consistent results. An endogenous nitrogen level of 31.9 mg of nitrogen per kilogram of body weight was determined for lambs. Ruminal ammonia concentrations were significantly higher following the feeding of urea than they were following the feeding of any other nitrogen source. There was no significant difference between ruminal ammonia concentrations resulting from the feeding of gelatin, casein, soybean protein, or bovine blood fibrin. The mean biological values (calculated using metabolic nitrogen expressed on the basis of excreted dry matter) of the nitrogen sources were: urea, 53.7; gelatin, 57.4; casein, 72.7; soybean protein, 82.4; and bovine blood fibrin, 83.1. The biological values of bovine blood fibrin and soybean protein were significantly larger (P < 0.05) than that of casein, however, the casein values were significantly larger (P < 0.01) than those of gelatin and urea.