Quinn M J, Reinhardt C D, Loe E R, Depenbusch B E, Corrigan M E, May M L, Drouillard J S
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-1600, USA.
J Anim Sci. 2008 Apr;86(4):902-8. doi: 10.2527/jas.2007-0117. Epub 2008 Jan 11.
Two experiments were conducted at the Kansas State University Beef Cattle Research Center to determine the effects of ractopamine-HCl (Optaflexx) on growth performance, carcass characteristics, and meat quality of finishing feedlot heifers. In Exp. 1, heifers implanted with Revalor-H (n = 302, initial BW = 479 kg) were fed steam-flaked corn diets with 0 (control) or 200 mg of ractopamine-HCl (OPT) per heifer daily for 28 d before slaughter. Average daily gain and DMI were not different between treatments (P > 0.17); however, OPT cattle tended to have a greater G:F (P = 0.06). Treatments did not differ with respect to final BW, HCW, dressing percentage, USDA yield grade, USDA quality grade, marbling score, LM area, KPH, Warner-Bratzler shear force, weight loss during cooking, or L*, a*, or b* colorimetric values during a 7-d retail display or purge loss from loin steaks during retail display (P > 0.19). In Exp. 2, nonimplanted crossbred heifers (n = 281, BW = 451 +/- 2 kg) were fed finishing diets based on steam-flaked corn. A control diet (no ractopamine) was compared with diets providing 200 mg of OPT per heifer daily for periods of 28 or 42 d (200 x 28 and 200 x 42, respectively), 300 mg/d for 28 d (300 x 28), and a step-up regimen consisting of 14 d at 100 mg, followed by 14 d at 200 mg, and the final 14 d at 300 mg of OPT (step-up). Feeding OPT had no effect on carcass weight gain among treatments (P = 0.18). The efficiency of carcass gain was 34 and 35% greater (P = 0.06) for the 200 x 42 and step-up groups compared with control, respectively. Feeding OPT at 300 mg for 28 d reduced DMI compared with the control, 200 x 28, and 200 x 42 (P < 0.05) groups. Administration of OPT had no effect on marbling score, yield grade, LM area, KPH, or percentages of carcasses grading USDA Choice (P > 0.10). Feeding ractopamine-HCl (Optaflexx) to finishing heifers generally improved the efficiency of carcass gain with minimal effect on carcass characteristics. These effects were most pronounced in heifers fed ractopamine for 42 d.
在堪萨斯州立大学肉牛研究中心进行了两项试验，以确定盐酸莱克多巴胺（Optaflexx）对育肥牛场育成母牛生长性能、胴体特征和肉质的影响。在试验1中，植入了Revalor-H（n = 302，初始体重 = 479千克）的育成母牛在屠宰前28天每天饲喂含0（对照）或200毫克盐酸莱克多巴胺（OPT）的蒸汽压片玉米日粮。各处理间平均日增重和干物质采食量无差异（P > 0.17）；然而，OPT组牛的料重比有增加的趋势（P = 0.06）。各处理在最终体重、热胴体重、屠宰率、美国农业部产量等级、美国农业部质量等级、大理石花纹评分、腰大肌面积、肾周脂肪、沃纳-布拉茨勒剪切力、烹饪过程中的失重或7天零售展示期间的L*、a或b比色值或零售展示期间腰大肌牛排的渗出损失方面无差异（P > 0.19）。在试验2中，未植入的杂交育成母牛（n = 281，体重 = 451 ± 2千克）饲喂基于蒸汽压片玉米的育肥日粮。将对照日粮（不含莱克多巴胺）与分别为每头育成母牛每天提供200毫克OPT持续28天或42天（分别为200×28和200×42）、300毫克/天持续28天（300×28）以及由14天100毫克、接下来14天200毫克、最后14天300毫克OPT组成的递增方案（递增）进行比较。饲喂OPT对各处理间的胴体增重无影响（P = 0.18）。与对照组相比，200×42组和递增组的胴体增重效率分别提高了34%和35%（P = 0.06）。与对照组、200×28组和200×42组相比，300毫克/天持续28天饲喂OPT降低了干物质采食量（P < 0.05）。施用OPT对大理石花纹评分、产量等级、腰大肌面积、肾周脂肪或美国农业部精选级胴体的百分比无影响（P > 0.10）。给育成母牛饲喂盐酸莱克多巴胺（Optaflexx）通常可提高胴体增重效率，对胴体特征影响最小。这些影响在饲喂莱克多巴胺42天的育成母牛中最为明显。
