Effects of a slow-release urea source on absorption of ammonia and endogenous production of urea by cattle

G. B. Huntington, D. L. Harmon, N. B. Kristensen, K. C. Hanson, J. W. Spears

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49 Scopus citations


Three experiments were conducted with Angus or Holstein steers to evaluate effects of dietary urea-calcium (a slow rumen-release urea source) on absorption of ammonia N from the gut and urea N production in the liver. Steers were fed a high-grain diet (Experiment 1) or an all-forage diet (Experiments 2 and 3). Urea or urea-calcium (0.25 g/kg body weight) was dosed into the esophagus (Experiments 1 and 2) or rumen (Experiment 3), and blood samples were serially collected for 180 min. Blood concentrations of ammonia N and urea N were measured in all experiments, and net flux of metabolites across splanchnic tissues was measured in Experiment 3. Compared to urea, urea-calcium reduced (P<0.05) plasma concentrations of ammonia N in steers fed all-forage diets, and tended (P<0.06) to reduce arterial glucose concentrations in Experiment 3. Plasma concentrations of urea N were not affected by treatment in any experiment. Treatment and time post-dosing interactions (P<0.05) in Experiment 3 were due to increased ruminal fluid concentrations of ammonia N, net release of ammonia N by portal-drained viscera and total splanchnic tissues with urea versus urea-calcium treatment shortly after dosing. Similar interactions (P<0.05) indicated that urea caused higher hepatic glucose release and increased l-lactate release by total splanchnic tissues after dosing than urea-calcium. Urea-calcium was effective in mitigating rapid ammonia release in the rumen and subsequent effects on glucose and lactate metabolism.

Original languageEnglish
Pages (from-to)225-241
Number of pages17
JournalAnimal Feed Science and Technology
Issue number3-4
StatePublished - Nov 1 2006

Bibliographical note

Funding Information:
This research was supported in part by Unipro International, Greeley, CO, USA. Authors thank Ms. Lucile Ganey and Ms. Karen Murphy for their able laboratory work, and personnel at the Butner Beef Cattle Research Center for care and feeding of the steers.


  • Ammonia
  • Rumen
  • Steers
  • Urea

ASJC Scopus subject areas

  • Animal Science and Zoology


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