In Vitro 15Nitrogen-tracer Technique for Some Kinetic Measures of Ruminal Ammonia

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Abstract
To quantitate the several nitrogen fluxes which participate in the synthesis of ru- minal microbes, an in vitro technique uti- lizing 15N ammonia was developed. The technique involves incubation of 15NH4- labelled rumen contents and analysis for 15N-ammonia and total ammonia N at spe- cific time intervals during the incubation period. For a cow fed twice daily and a sheep fed at 2-hourly intervals, respec- tively, the technique yielded estimates of mean fractional turnover rates (Kam) of .226 and .314 per hour, and mean rates of ammonia nitrogen incorporation into cell materials (am) of 2.68 and 2.89 mg per hour per 50 g of whole rmnen digesta. The effect of rumen content donor on Kam was highly significant (P < 0.01) ; but the effect of am was not significant. For sheep fed alfalfa pellets continuously, about 9.2 g of ruminal microbial cells per 100 g di- gestible organic matter fed are synthesized via ammonia nitrogen and about 61% of microbial nitrogen is derived from am- monia _N. Presumably, 39% is derived from other nitrogen sources such us amino acid and peptide nitrogen.