Gleghorn J F, Elam N A, Galyean M L, Duff G C, Cole N A, Rivera J D
New Mexico State University Clayton Livestock Research Center, Clayton 88415, USA.
J Anim Sci. 2004 Sep;82(9):2705-17. doi: 10.2527/2004.8292705x.
Two experiments were conducted at two locations to determine the effects of dietary CP concentration and source on performance, carcass characteristics, and serum urea nitrogen (SUN) concentrations of finishing beef steers. British x Continental steers were blocked by BW (357 +/- 28 and 305 +/- 25 kg initial BW; n = 360 and 225; four and five pens per treatment in Exp. 1 and 2, respectively). Steam-flaked corn-based diets were arranged in a 3 x 3 factorial with three CP concentrations (11.5, 13, or 14.5% of DM) and three sources of supplemental CP (N basis): 100% urea; 50:50 blend of urea and cottonseed meal; or 100% cottonseed meal. Steers in both experiments were initially implanted with Ralgro and reimplanted with Revalor-S on d 56. Performance and carcass data were pooled across locations. Crude protein concentration x source interactions were not observed (P = 0.22 to 0.93) for performance and carcass data. Crude protein concentration affected ADG (P = 0.02) and carcass-adjusted (to a common dressing percent within location) ADG quadratically (P = 0.06). Increasing the concentration of supplemental urea linearly increased carcass-adjusted ADG and G:F (P < 0.05) and carcass-adjusted G:F (P < 0.001). Dry matter intake was not affected (P = 0.93) by either CP concentration or source. Hot carcass weight (HCW; P = 0.02), LM area (P = 0.05), and dressing percent (P = 0.03) increased linearly with increasing urea concentration, whereas increasing CP concentration quadratically affected HCW (P = 0.02), with a maximum at 13% CP. Differences in backfat thickness and yield grade were negligible across treatments. Neither marbling score nor percentage of carcasses grading USDA Choice was affected by CP concentration or source. At all times measured, SUN concentrations increased (P < 0.05) with increasing CP concentration, but effects of CP source were small and variable across time. Results indicate that increasing CP concentrations from 11.5 to 13% slightly increased ADG and carcass-adjusted ADG, whereas increasing the proportion of supplemental urea increased carcass-adjusted ADG, G:F, and carcass-adjusted G:F and increased HCW, LM area, and dressing percent. A CP concentration above 13% seemed detrimental to ADG and HCW. Serum urea N increased over time, with CP concentration having a greater effect than CP source.
在两个地点进行了两项试验,以确定日粮粗蛋白(CP)浓度和来源对育肥牛性能、胴体特征及血清尿素氮(SUN)浓度的影响。英国品种与欧洲大陆品种杂交的阉牛按体重(初始体重分别为357±28千克和305±25千克;试验1和试验2分别有360头和225头;试验1和试验2每个处理分别有4个和5个围栏)进行分栏。以蒸汽压片玉米为基础的日粮按3×3析因设计,有三种CP浓度(占干物质的11.5%、13%或14.5%)和三种补充CP来源(以氮计):100%尿素;尿素与棉籽粕各50%的混合物;或100%棉籽粕。两个试验中的阉牛最初均植入Ralgro,并在第56天重新植入Revalor-S。性能和胴体数据在不同地点进行汇总。未观察到粗蛋白浓度×来源对性能和胴体数据的交互作用(P=0.22至0.93)。粗蛋白浓度影响平均日增重(ADG,P=0.02),且对胴体校正(至同一地点内相同屠宰率)ADG有二次效应(P=0.06)。增加补充尿素的浓度可使胴体校正ADG和料重比(G:F)呈线性增加(P<0.05),且胴体校正G:F增加(P<0.001)。干物质采食量不受CP浓度或来源的影响(P=0.93)。热胴体重(HCW,P=0.02)、眼肌面积(P=0.05)和屠宰率(P=0.03)随尿素浓度增加呈线性增加,而增加CP浓度对HCW有二次效应(P=0.02),在CP为13%时达到最大值。各处理间背膘厚度和产肉等级差异可忽略不计。大理石花纹评分和美国农业部(USDA)精选级胴体的百分比均不受CP浓度或来源的影响。在所有测定时间,SUN浓度随CP浓度增加而升高(P<0.05),但CP来源的影响较小且随时间变化不定。结果表明,将CP浓度从11.5%提高到13%可使ADG和胴体校正ADG略有增加,而增加补充尿素的比例可使胴体校正ADG、G:F和胴体校正G:F增加,并使HCW、眼肌面积和屠宰率增加。CP浓度高于13%似乎对ADG和HCW不利。血清尿素氮随时间增加,CP浓度的影响大于CP来源。