Ruminal nitrogen metabolism in steers as affected by feed intake and dietary urea concentration.
Four multiple-cannulated steers (340 kg) were used in a 4 X 4 Latin square design with a 2 X 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.
Department of Animal Sciences, University of Illinois, Urbana 61801.
J L
JL
Firkins
L L
LL
Berger
N R
NR
Merchen
G C
GC
Fahey
R L
RL
Mulvaney
D000821:Animal Feed; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004755:Enterobacteriaceae / Q000378:metabolism; D056890:Eukaryota / Q000378:metabolism; D008297:Male; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes; D012417:Rumen / Q000378:metabolism* / Q000382:microbiology; D014508:Urea / Q000008:administration & dosage / Q000494:pharmacology*
D009587:Nitrogen Isotopes; D014508:Urea; D009584:Nitrogen