Department of Animal Science, Oklahoma State University, Stillwater 74078, USA.
J Anim Sci. 2010 Jan;88(1):338-48. doi: 10.2527/jas.2009-1798. Epub 2009 Sep 11.
The objective was to evaluate the effects of an extended withdrawal period after feeding the beta-adrenergic agonist zilpaterol hydrochloride (ZH) for 20 d at the end of the feeding period. Three hundred eighty-four crossbred beef steers were blocked by BW and randomly allocated into 64 pens (6 steers/pen). Pens were assigned to treatments in a 2 x 4 factorial arrangement in a randomized complete block design. Main effects were the addition of 0 (control) or 8.3 mg/kg of ZH (DM basis) to the finishing diet for 20 d before estimated average slaughter date and paired withdrawal periods of 3, 10, 17, or 24 d before slaughter. Individual BW were measured initially, 1 d before ZH feeding, and 1 d before slaughter. The ZH feeding period was initiated so that control cattle in the 3-d withdrawal group would be expected to average 65% USDA Choice Quality grade and have 1.27 cm of 12th-rib fat based on visual appraisal. Carcass data were collected at slaughter. For the 3-d withdrawal steers, 2 steers from each pen were selected to determine visceral organ and total offal mass at slaughter. The ZH x withdrawal day interaction was not significant (P > 0.10) for the majority of variables. There was no difference (P > or = 0.12) due to ZH feeding for final BW, carcass-adjusted final BW, or ADG. However, DMI was decreased (P = 0.02) and G:F increased (P = 0.01) in steers fed ZH vs. control steers. As day after withdrawal of ZH increased, there was a linear increase (P < 0.001) in final BW and carcass-adjusted final BW, but a linear decrease (P < 0.001) in ADG over the finishing period and over the ZH plus withdrawal period. Overall, HCW was 380 and 369 kg (P < 0.001) for ZH and control steers, respectively. However, the difference between ZH and control was 14, 17, 5, and 6 kg with 3, 10, 17, and 24 d withdrawal, respectively (ZH x withdrawal day, P = 0.09). Feeding ZH increased dressing percentage (65.8 vs. 64.6%; P < 0.001) and LM area (94.8 vs. 89.7 cm(2); P < 0.001), and decreased calculated yield grade (2.69 vs. 2.91; P = 0.03) and percentage of cattle grading USDA Choice (31.1 vs. 42.3%; P = 0.03) compared with controls. Small intestinal mass (g/kg of empty BW) was greater (P = 0.03) for steers fed ZH compared with controls. There were no other differences (P > or = 0.11) in mass of body components, expressed in kilograms or as a fraction of empty BW. In this experiment, improvements in animal performance and HCW due to feeding ZH were generally maintained when withdrawal was extended through 10 d.
目的是评估在育肥期结束时，β-肾上腺素激动剂盐酸齐帕特罗（ZH）连续 20 天喂养结束后延长停药期的效果。384 头杂交肉牛按 BW 分组，随机分配到 64 个围栏（每栏 6 头）。围栏按 2 x 4 析因设计，在随机完全区组设计中分配处理。主要效应是在育肥期结束前 20 天，在基础日粮中添加 0（对照）或 8.3mg/kg 的 ZH，然后进行 3、10、17 或 24 天的停药期。在初始、ZH 喂养前 1 天和屠宰前 1 天分别测量个体 BW。ZH 喂养期开始时，预计对照组 3d 停药组的牛平均 USDA 选择质量等级为 65%，12 肋脂肪厚度为 1.27cm，基于视觉评估。屠宰时收集 carcass 数据。对于 3d 停药组，每栏选择 2 头进行屠宰时内脏器官和总杂碎质量的测定。ZH x 停药日的交互作用对大多数变量没有显著影响（P>0.10）。由于 ZH 喂养，最终 BW、 carcass-adjusted 最终 BW 和 ADG 没有差异（P>或=0.12）。然而，与对照组相比，ZH 喂养的牛 DMI 降低（P=0.02），G:F 增加（P=0.01）。随着 ZH 停药天数的增加，最终 BW 和 carcass-adjusted 最终 BW 呈线性增加（P<0.001），但在育肥期和 ZH 加停药期的 ADG 呈线性下降（P<0.001）。总的来说，ZH 和对照组的 HCW 分别为 380 和 369kg（P<0.001）。然而，ZH 和对照组之间的差异分别为 14、17、5 和 6kg，停药时间分别为 3、10、17 和 24d（ZH x 停药日，P=0.09）。ZH 喂养增加了服装百分比（65.8%比 64.6%；P<0.001）和 LM 面积（94.8 比 89.7cm2；P<0.001），降低了计算的产量等级（2.69 比 2.91；P=0.03）和 USDA 选择等级的牛比例（31.1%比 42.3%；P=0.03）与对照组相比。与对照组相比，ZH 喂养的牛小肠质量（每空 BW 的克数）增加（P=0.03）。其他质量（以千克或空 BW 的分数表示）无差异（P>或=0.11）。在本实验中，由于 ZH 喂养而导致的动物性能和 HCW 的改善在延长停药期至 10d 时基本保持。
