饲粮尿素添加水平对生长育肥牛生长性能和血液生化指标的影响

Effect of Dietary Urea Supplementation Level on Growth Performance and Blood Biochemical Indices in Growing-Finishing Cattle

【目的】利用肉牛饲养试验研究饲粮尿素添加水平对生长育肥牛生长性能和血液生化指标的影响,为肉牛生产中合理添加尿素提供理论依据。【方法】选择60头利木赞×复洲杂交的F1公牛,随机分为6组,每组10头,分别接受1个尿素添加水平的饲粮处理。设置6个粗蛋白和代谢能值相近(14%CP,11.3 MJ.kg-1,DM基础)的饲粮处理,其中尿素添加量分别为0%(对照)、0.4%、0.8%、1.2%、1.6%和2.0%。试验期14周,其中预饲期1周,正试期13周。【结果】随尿素添加水平的提高,干物质摄入量(dry matter intake,DMI)无显著变化(P>0.1),但日增重呈线性规律显著下降(L,P<0.05),饲料转化效率(DMI/ADG(average daily gain))呈现线性规律显著上升(L,P<0.05)。其中,尿素添加水平在0.8%以内未见日增重和饲料转化效率(DMI/ADG)有显著变化。提高饲粮尿素添加水平,血氨浓度线性上升(L,P<0.001);而血浆总蛋白和血浆尿素氮(plasma urea-N,PUN)浓度呈二次曲线规律升高(Q,P<0.001),其中血浆总蛋白和PUN浓度分别在1.50%和0.64%(%DM)尿素添加水平下出现拐点。提高饲粮尿素添加水平对谷丙转氨酶活性没有显著影响(P>0.1),但会导致谷草转氨酶活性呈线性升高(L,P<0.001)。在反映肉牛应激状况的激素指标中,除肾上腺素外,肌酸激酶活性、去甲肾上腺素、皮质醇、皮质酮和醛固酮浓度等均呈显著的二次曲线规律上升或下降(Q,P<0.05);其中,上升或下降趋势的变化出现在0.8%—1.2%尿素添加水平。【结论】生长育肥牛饲粮中尿素添加水平在0.8%以内,或尿素氮占总氮比例在16%以内,可认为是适宜的安全添加水平。

【Objective】A feeding trial was designed to investigate the effect of dietary urea levels on growth performance and blood biochemical indexes of growth-finishing cattle for providing a theoretical basis for the optimum level of urea supplementation in beef cattle diet.【Method】 Sixty growing-finishing Limousin×Fuzhou crossbred bulls were randomly selected and divided into six groups with 10 bulls in each treatment group.The treatment diets were six supplemental urea levels（0,0.4,0.8,1.2,1.6 and 2.0%） in the complete diet and contained similar CP and ME concentrations（14%CP,11.3 MJ·kg-1 on DM basis）.The trail was lasted for a total of 14 wks including 1 wk for adaptation and 13 wks for data collection.【Result】 As dietary urea level increased,daily DM intake was not different significantly（P0.10）,but ADG was linearly decreased（L,P0.05）,and feed conversion efficiency（DMI/ADG） was linearly increased（L;P0.05）.There was no significant response in ADG and feed conversion efficiency（DMI/ADG） within 0.8% of dietary urea level.Increasing dietary urea-N level resulted in remarkable increases in plasma ammonia（L,P0.001）,total proteins（Q,P0.001） and urea-N（Q;P0.05） with break points of total plasma proteins and plasma urea-N appearing at 1.50% and 0.64% of dietary urea supplementation level,respectively.When dietary urea level increased,blood alanine aminotransferase（ALT） activity was unchanged significantly（P0.1）,but aspartate aminotransferase（AST） activity linearly increased（L,P0.001）.Increasing dietary urea-N level quadratically（Q,P0.05） affected the concentrations of blood biochemical indices in relation to stress reaction,such as the activity of serum creatine kinase,concentrations of norepinephrine（NE）,corticosteroid（COR） corticosterone and aldosterone（ALD） except epinephrine（E）,with altered trends obtained between 0.8%-1.2% of dietary urea supplementation level.【Conclusion】 Considering the result of the growth performance and blood biochemical indices,urea inclusion level of lower than 0.8% in the growing-finishing diet DM was be recommended as an optimal and safe level,which is equivalent to 16% of urea-N of total dietary N.