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

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 of BW) to monitor the behavior of SRU in the ruminal environment. Compared with 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 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 concentration 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 concentrations but was equivalent to urea at the 0.8 and 1.2% supplementation concentrations; these effects were due to urea source x concentration 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%) concentrations but is equivalent to urea at 0.8 and 1.2% concentrations.

Effect of diets differing in rumen soluble nitrogen on utilization of poor-quality roughage by sheep

“…Differences in pH were observed between Treatments 1 and 2 at 06:00 and between Treatment 1 and Treatments 2, 3 and 5 at 21:00 (P <0.05) (Figure 2). Taylor-Edwards et al (2009b) found similar results in terms of pH between urea and SRU treatments. In contrast, Wahrmund et al (2007), reported that rumen pH tended to be affected by urea source, where Optigen® II tended to have a lower pH than the control and urea treatments.…”

“…The observed low N retention for Treatment 5 could be related to high N excretion, low apparent N digestibility and the low N intake. In contrast with the findings of this study, Taylor-Edwards et al (2009b) found higher faecal N for slow-release urea (SRU) compared with urea. These authors suggested that these findings could be possible only if some of the SRU passed through the digestive tract without being hydrolysed in the rumen.…”

“…Consequently, some of the Optigen® II might have left the rumen without being hydrolysed or incorporated into rumen microbial protein. Lack of difference in terms of apparent digestibility of DM, OM and NDF among treatments was reported by Taylor-Edwards et al (2009b). These authors reported a significantly lower N digestibility with the polymer-coated slow-release urea (SRU) treatment than for the urea treatment.…”

“…In line with this study, Bourg et al (2009) recorded no differences between urea and Optigen® II treatments for faecal and urinary N excretion. The present study showed that treatments containing higher levels of Optigen® II had higher N excretion (faecal and urinary) values (Table 4), suggesting that N released from Optigen® II might not have been captured in microbial crude protein (MCP) during the early hours of fermentation (Galo et al, 2003;Taylor-Edwards et al, 2009b).…”

“…To overcome this limitation and reduce risks of urea toxicity in ruminants, various options have been evaluated over the years, such as creating slow-release N sources. These technologies are used to improve synchrony between available energy and N in the rumen to maximize microbial protein synthesis, and minimize the risk of NH 3 -N toxicity (Harrison & Karnezos, 2005;Taylor-Edwards et al, 2009b). The aim of using a slow-release N source is to provide a slow, even release of N over 24 hours, and meet the N requirements of rumen bacteria when rumen NH 3 -N levels are expected to be low after the ingestion of urea.…”