利用60头生长期利木赞杂交牛[(393.7±15.6) kg]进行饲养试验，以研究淀粉糊化尿素添加水平对肉牛生长性能以及血浆生化指标的影响，为生产中安全利用淀粉糊化尿素（gelatinized starch-urea，GSU）提供科学依据。动物随机分为6组，每组1个重复，每个重复10头牛。对照组饲粮中不添加GSU，处理饲粮以GSU来源氮分别占饲粮总氮的8%、16%、24%、32%和40%。试验期14周，其中预试期1周，正试期13周。结果表明，各处理间干物质采食量（7.93～8.34 kg/d）、平均日增重（1.13～1.27 kg/d）及饲料转化效率（0.140～0.157）均无显著差异（P>0.10）。随饲粮GSU添加水平的提高，血浆尿素氮线性升高（L；P<0.01），而血氨和血浆总蛋白含量呈二次曲线规律升高（Q；P<0.001）。添加GSU对血浆谷丙转氨酶活性未见显著影响（P>0.05），但导致谷草转氨酶活性线性升高（L；P<0.01）。本试验结论：生长育肥牛饲粮中GSU占饲粮总氮25%，或来源于GSU的尿素占饲粮干物质比例在1.27%以内，可以认为是安全的添加水平。
A feeding trial was conducted to investigate the effect of supplemental levels of gelatinized starch-urea (GSU) on growth performance and plasma biochemical indices of growing-finishing beef cattle. Sixty Limousin crossbred bulls [(393.7±15.6) kg] were randomly allotted into six groups with 1 replicate each and 10 bulls in each replicate. The bulls in the six groups were fed diets with no supplemental GSU (control) or supplemented with nitrogen from GSU (GSU-N) at 8%, 16%, 24%, 32% or 40% of total dietary nitrogen, respectively. Results showed that dry matter intake (7.93 to 8.34 kg/d), average daily gain (1.13 to 1.27 kg/d) and feed conversion ratio (0.140 to 0.157) had no significant difference among all the treatments (P>0.10). Increasing supplemental level of GSU linearly increased plasma urea nitrogen concentration (L; P<0.01) and quadratically increased plasma total protein and plasma ammonia concentrations (Q; P<0.001). In addition, the plasma aspartate aminotransferase (AST) activity increased linearly with increasing GSU levels (L; P<0.01), whereas the GSU level had no significant effect on plasma alanine aminatransferaie (ALT) activity (P>0.05). In conclusion, it is considered that 25% GSU-N to diet total N ratio or less than 1.27% GSU-urea to diet dry matter ratio is a safe additive level for growing-finishing beef cattle.［Chinese Journal of Animal Nutrition, 2011, 23（10）：1710 -1715］
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