Ruminal Nitrogen Metabolism in Steers as Affected by Feed Intake and Dietary Urea Concentration

J. L. Firkins, L. L. Berger, N. R. Merchen, G. C. Fahey, R. L. Mulvaney

Research output: Contribution to journalArticlepeer-review


Four multiple-cannulated steers (340 kg) were used in a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Steers were fed a diet of 50% ground hay and 50% concentrate at two intakes (1.4 and 2.1% of BW), with urea and 15N-enriched ammonium sulfate infused continuously into the rumen at .4 or 1.2% of diet DM. Ratios of purines and diaminopimelic acid-N to N in fluid-associated and particulate-associated bacteria and in protozoa were similar among treatments but were lower for protozoa than for bacteria. Diaminopimelic acid-N:N was higher for fluid-associated vs. particulate-associated bacteria. Enrichment of 15N was similar between bacteria among treatments and was 30% lower for protozoa. Turnover rates of 15N in bacteria, NH3N, and non-NH3N pools were faster for steers infused with 1.2 than those infused with .4% urea, indicating less efficient usage of ammonia with higher urea. A method is described to estimate the proportion of duodenal nitrogen comprising bacterial and protozoal nitrogen.

Original languageEnglish (US)
Pages (from-to)2302-2311
Number of pages10
JournalJournal of Dairy Science
Issue number11
StatePublished - 1987

ASJC Scopus subject areas

  • Food Science
  • Animal Science and Zoology
  • Genetics


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