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

To quantitate the several nitrogen fluxes which participate in the synthesis of ruminal microbes, an in vitro technique utilizing 15N ammonia was developed. The technique involves incubation of 15NH4labelled rumen contents and analysis for 15N-ammonia and total ammonia N at specific time intervals during the incubation period. For a cow fed twice daily and a sheep fed at 2-hourly intervals, respectively, 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.