Taylor-Edwards C C, Hibbard G, Kitts S E, McLeod K R, Axe D E, Vanzant E S, Kristensen N B, Harmon D L
Department of Animal and Food Sciences, University of Kentucky, Lexington 40546-0215, USA.
J Anim Sci. 2009 Jan;87(1):200-8. doi: 10.2527/jas.2008-0912. Epub 2008 Sep 26.
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.
进行了两项试验，以评估缓释尿素（SRU）与饲料级尿素对阉牛瘤胃代谢物特征以及生长肉牛的干物质采食量（DMI）、增重和料重比（G:F）的影响。试验1选用12头装有瘤胃瘘管的阉牛（体重529±16千克），监测SRU在瘤胃环境中的行为。与饲料级尿素相比，SRU降低了瘤胃氨浓度（P = 0.02），且有提高瘤胃脲酶活性的趋势（P = 0.06），但对瘤胃挥发性脂肪酸（VFA）摩尔比例或总浓度无影响（P>0.20）。饲喂35天后，饲喂尿素或SRU的动物之间，SRU的原位降解率无差异（P = 0.48）。试验2选用180头安格斯杂交阉牛（体重330±2.3千克），给以玉米青贮为基础的日粮补充尿素或SRU，饲喂56天，以评估对采食量、增重和G:F的影响。试验设计为随机完全区组，采用2×4 + 1析因处理排列。处理包括不补充尿素（对照），或按日粮干物质的0.4%、0.8%、1.2%或1.6%补充尿素或SRU。在整个56天的试验中，尿素来源×浓度对增重（P = 0.04）和G:F（P = 0.01）存在交互作用，因为在0.4%和1.6%的补充浓度下，SRU降低了平均日增重（ADG）和G:F，但在0.8%和1.2%的补充浓度下与尿素相当；这些影响是由于试验第29至56天期间，尿素来源×浓度对增重（P = 0.06）和G:F（P = 0.05）的交互作用。SRU在第29至56天降低了DMI（P = 0.01），但在第0至28天没有降低，因此在整个试验中，尿素来源对DMI没有差异（P = 0.19）。这些综合结果表明，SRU在瘤胃中缓慢释放氮，35天内无明显适应性变化。低浓度（0.4%）补充SRU可能会限制氮的可利用性，但在0.8%和1.2%浓度下与尿素相当。
