Nitrogen (15N) Utilization and Microbial Protein Synthesis in the Rumen of Urea Fed Cattle

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Abstract
Two adult Fresian bulls fitted with permanent rumen fistulae were fed a high fiber diet in which 33% of the nitrogen was urea. The ration was offered in two equal portions every 12 hours. Samples of whole rumen contents were withdrawn before feeding and at 1, 2, 4, 6, 8 and 10 hr after feeding. Rates of ammonia-N incorporation into microbial protein using (15NH4)2SO4 (30% enriched), and volatile fatty acids were determined in each sample in vitro. Rumen volumes were measured using CrEDTA. Microbial protein synthesis determined by the use of 15N was compared with that estimated by DAP and AEP Markers. The mean rate of ammonia nitrogen incorporation into microbial cells was 23.12 mg/hr/kg. of rumen contents; this was calculated to equal a synthesis of 59.9 g of microbial nitrogen daily. The mean rate of VFA production of rumen contents incubated was found to be 11.5 mMoles/ kg/hr which was calculated to provide 42.3 moles ATP/day. The microbial cell yield per mole ATP (YATP) was calculated to be 13.5 grams. The mean microbial nitrogen incorporation in the rumen contents using DAP and AEP as markers for bacterial and protozoal-N, respectively, was 50.6 g daily. This value is similar to the value obtained from 15N incorporation in microbial cell. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.