Department of Animal Science, University of Illinois, Champaign-Urbana, 1503 S Maryland Dr, Urbana 61801, USA.
J Anim Sci. 2010 May;88(5):1823-9. doi: 10.2527/jas.2009-2405. Epub 2009 Dec 30.
Ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH) are beta-adrenergic agonists that improve growth performance and affect carcass characteristics. The objective of this study was to evaluate the comparative effects of RAC and ZH when fed to beef steers during the last 33 d of the finishing period. Three hundred crossbred beef steers (516 +/- 8 kg) were grouped by BW, BCS, and breed type and randomly assigned to 1 of 3 treatments (10 steers per pen; 10 pens per treatment). Treatments were control (no beta-agonists added), RAC (200 mg of ractopaminexhdx(-1)d(-1), for 33 d), or ZH (75 mg of zilpaterolxanimalx(-1)d(-1), for 30 d, removed 3 d for required withdrawal period). Steers were slaughtered, carcass characteristics were evaluated, and cut-out yields were determined. Both RAC and ZH increased final BW, ADG, feed efficiency (G:F), and HCW compared with controls (P < 0.05). Compared with RAC, ZH decreased ADG, ADFI, and final BW, but increased HCW and dressing percentage (P < 0.05). Carcass yield was not affected by RAC in this experiment, whereas ZH decreased adjusted fat thickness and KPH, increased ribeye area, improved yield grade, and increased cut-out yields, when compared with controls (P < 0.05). Marbling, lean maturity, and skeletal maturity were not different between treatments (P > 0.05). Steaks from RAC steers had greater (P < 0.05) Warner-Bratzler shear force (WBSF) values than steaks from control steers at 3 and 7 d of aging, but did not differ from controls after 14 d of aging. Steaks from ZH steers had greater WBSF values (P < 0.05) than steaks from controls and RAC steaks throughout the 21-d postmortem aging period. Although both beta-adrenergic agonists were effective at improving feedlot performance, RAC showed no negative effect on WBSF after 14 d, whereas WBSF values for ZH steaks were significantly greater than controls after 21 d.
盐酸莱克多巴胺（RAC）和盐酸齐帕特罗（ZH）是β-肾上腺素能激动剂，可改善生长性能并影响胴体特性。本研究的目的是评估在育肥期最后 33 天内，给肉牛饲喂 RAC 和 ZH 的比较效果。将 300 头杂交肉牛（516±8kg）按体重、体况评分和品种分组，并随机分配到 3 种处理组之一（每栏 10 头牛；每处理 10 栏）。处理组为对照组（未添加β-激动剂）、RAC 组（200mg 莱克多巴胺xhdx(-1)d(-1)，连续 33 天）或 ZH 组（75mg 齐帕特罗xanimalx(-1)d(-1)，连续 30 天，停药期 3 天）。屠宰肉牛，评估胴体特性，并确定切块产量。与对照组相比，RAC 和 ZH 均提高了终重、ADG、饲料效率（G:F）和 HCW（P<0.05）。与 RAC 相比，ZH 降低了 ADG、ADFI 和终重，但增加了 HCW 和出肉率（P<0.05）。本试验中，RAC 对胴体产肉率没有影响，而 ZH 降低了调整后的脂肪厚度和 KPH，增加了眼肌面积，提高了产肉等级，并增加了切块产量，与对照组相比（P<0.05）。大理石花纹、瘦肉成熟度和骨骼成熟度在处理组之间没有差异（P>0.05）。RAC 牛的牛排在 3 和 7 天老化时的 Warner-Bratzler 剪切力（WBSF）值高于对照组，但在 14 天老化后与对照组没有差异。ZH 牛的牛排在整个 21 天死后老化期间的 WBSF 值均高于对照组和 RAC 牛的牛排（P<0.05）。虽然两种β-肾上腺素能激动剂都能有效提高育肥性能，但 RAC 在 14 天后对 WBSF 没有负面影响，而 ZH 牛的牛排在 21 天后的 WBSF 值明显高于对照组。
