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Effects of slow-release urea on ruminal digesta characteristics and growth performance in beef steers

C. C. Taylor-Edwards^*, G. Hibbard^*, S. E. Kitts^*, K. R. McLeod^*, D. E. Axe, E. S. Vanzant^*, N. B. Kristensen and D. L. Harmon^*

^* Department of Animal and Food Sciences, University of Kentucky, Lexington 40546-0215 , Agri-Nutrients Technology Group, Petersburg, VA, 23803 University of Aarhus, Faculty of Agricultural Sciences, Tjele, DK-8830, Denmark

dharmon{at}uky.edu

Abstract

Two experiments were conducted to evaluate the effects of slow-release urea (SRU) versus feed-grade urea on ruminal metabolite characteristics in steers and DMI, gain, and G:F in growing beef steers. Experiment 1 used 12 ruminally cannulated steers (529 ± 16 kg BW) to monitor the behavior of SRU in the ruminal environment. Compared to feed-grade urea, SRU decreased ruminal ammonia concentration (P = 0.02) and tended to increase ruminal urease activity (P = 0.06) without affecting ruminal VFA molar proportions or total concentrations (P > 0.20). After 35 d of feeding, the in situ degradation rate of SRU was not different between animals fed urea or SRU (P = 0.48). Experiment 2 used [REMOVED SEQ FIELD]180 Angus-cross steers (330 ± 2.3 kg) fed corn silage-based diets supplemented with urea or SRU for 56 d to evaluate the effects on feed intake, gain, and G:F. The design was a randomized complete block with a 2 x 4 + 1 factorial arrangement of treatments. Treatments included no supplemental urea (control) or urea or SRU at 0.4, 0.8, 1.2, or 1.6% of diet DM. Over the entire 56 d experiment, there were interactions of urea source x level for gain (P = 0.04) and G:F (P = 0.01) because SRU reduced ADG and G:F at the 0.4 and 1.6% supplementation levels but was equivalent to urea at the 0.8 and 1.2% supplementation levels; these effects were due to urea source x level interactions for gain (P = 0.06) and G:F (P = 0.05) during d 29 to 56 of the experiment. The SRU reduced DMI during d 29 to 56 (P = 0.01) but not during d 0 to 28, so that over the entire experiment there was no difference in DMI for urea source (P = 0.19). These collective results demonstrate that SRU releases N slowly in the rumen with no apparent adaptation within 35 d. Supplementation of SRU may limit N availability at low (0.4%) levels but is equivalent to urea at 0.8 and 1.2% levels.

Key Words: metabolism • nitrogen • non-protein nitrogen • ruminant • steer • urea

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				C. C. Taylor-Edwards, N. A. Elam, S. E. Kitts, K. R. McLeod, D. E. Axe, E. S. Vanzant, N. B. Kristensen, and D. L. Harmon Influence of slow-release urea on nitrogen balance and portal-drained visceral nutrient flux in beef steers J Anim Sci, January 1, 2009; 87(1): 209 - 221. [Abstract] [Full Text] [PDF]