Farmer C G, Woods B C, Cochran R C, Heldt J S, Mathis C P, Olson K C, Titgemeyer E C, Wickersham T A
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66505, USA.
J Anim Sci. 2004 Mar;82(3):884-94. doi: 10.2527/2004.823884x.
Effect of supplementation frequency and supplemental urea level on forage use (Exp. 1) and performance (Exp. 2 and 3) of beef cattle consuming low-quality tallgrass-prairie were evaluated. For Exp. 1 and 2, a 2 x 2 factorial treatment structure was used, such that two supplements (30% CP) containing 0 or 30% of supplemental degradable intake protein (DIP) from urea were fed daily or on alternate days. In Exp. 1 and 2, supplement was fed at 0.41% BW daily or at 0.83% BW (DM basis) on alternate days. For Exp. 3, a 2 x 4 factorial treatment structure was used, such that four supplements (40% CP) containing 0, 15, 30, or 45% of supplemental DIP from urea were fed daily or 3 d/wk. Supplements were group-fed at 0.32% BW daily or at 0.73% BW (DM basis) 3 d/wk. In Exp. 1, 16 Angus x Hereford steers (initial BW = 252 kg) were blocked by BW and assigned to treatment. Urea level x supplementation frequency interactions were not evident for forage intake, digestion, or rate of passage. Forage OM intake (OMI) and total digestible OMI (TDOMI) were not significantly affected by treatment. Total-tract digestion of OM (P = 0.03) and NDF (P = 0.06) were greater for steers supplemented daily. In Exp. 2, 48 Angus x Hereford cows (initial BW = 490 kg) grazing winter tallgrass prairie were used. Significant frequency x urea interactions were not evident for BW and body condition (BC) change; similarly, the main effects were not substantive for these variables. In Exp. 3, 160 Angus x Hereford cows (initial BW = 525 kg) grazing dormant, tallgrass prairie were used. Supplement refusal occurred for cows fed the highest urea levels, particularly for cows fed the supplement with 45% of the DIP from urea 3 d/wk, and supplement refusal increased closer to calving. A frequency x urea interaction (P = 0.02) was observed for prepartum BW changes. As supplemental urea level increased, prepartum BW loss increased quadratically (P = 0.02); however, a greater magnitude of loss occurred when feeding supplements containing > or = 30% of DIP from urea 3 d/ wk. Cumulative BC change followed a similar trend. In conclusion, moderate protein (< or = 30% CP) supplements with < or = 30% of supplemental DIP from urea can be fed on alternate days without a substantive performance penalty. However, infrequent feeding of higher protein (> 30% CP) supplements with significant urea levels (> 15% of DIP from urea) may result in decreased performance compared with lower urea levels.
评估了补充频率和尿素补充水平对采食低质量高草草原牧草的肉牛的草料利用情况（实验1）以及生产性能（实验2和3）的影响。在实验1和2中，采用2×2析因处理结构，即每天或隔天饲喂两种补充料（粗蛋白含量30%），其中一种补充料含0%尿素可降解摄入蛋白（DIP），另一种含30%尿素可降解摄入蛋白。在实验1和2中，补充料的饲喂量按体重计分别为每天0.41%或隔天0.83%（干物质基础）。在实验3中，采用2×4析因处理结构，即每天或每周3天饲喂四种补充料（粗蛋白含量40%），分别含0%、15%、30%或45%尿素可降解摄入蛋白。补充料按体重计分别以每天0.32%或每周3天0.73%（干物质基础）进行群饲。在实验1中，16头安格斯×海福特阉牛（初始体重 = 252千克）按体重进行分组并分配至各处理组。在草料摄入量、消化率或通过率方面，尿素水平×补充频率的交互作用不明显。处理对草料有机物质摄入量（OMI）和总可消化有机物质摄入量（TDOMI）无显著影响。每天补充的阉牛的有机物质全肠道消化率（P = 0.03）和中性洗涤纤维消化率（P = 0.06）更高。在实验2中，使用了48头在冬季高草草原放牧的安格斯×海福特母牛（初始体重 = 490千克）。在体重和体况（BC）变化方面，频率×尿素的显著交互作用不明显；同样，这些变量的主效应也不显著。在实验3中，使用了160头在休眠期高草草原放牧的安格斯×海福特母牛（初始体重 = 525千克）。饲喂最高尿素水平的母牛出现了补充料拒食现象，尤其是每周3天饲喂含45%尿素可降解摄入蛋白补充料的母牛，且临近产犊时补充料拒食现象增多。观察到产前体重变化存在频率×尿素交互作用（P = 0.02）。随着尿素补充水平的增加，产前体重损失呈二次方增加（P = 0.02）；然而，当每周3天饲喂含≥30%尿素可降解摄入蛋白的补充料时，体重损失幅度更大。累积体况变化遵循类似趋势。总之，含≤30%尿素可降解摄入蛋白的中等蛋白（≤30%粗蛋白）补充料可以隔天饲喂，而不会对生产性能造成实质性影响。然而，与较低尿素水平相比，不频繁饲喂含大量尿素（>15%尿素可降解摄入蛋白）的高蛋白（>30%粗蛋白）补充料可能会导致生产性能下降。
