Winterholler S J, Parsons G L, Reinhardt C D, Hutcheson J P, Nichols W T, Yates D A, Swingle R S, Johnson B J
Department of Animal Sciences and Industry, Kansas State University, Manhattan, Kansas 66506, USA.
J Anim Sci. 2007 Feb;85(2):413-9. doi: 10.2527/jas.2006-555.
Yearling steers (n = 2,552; 314 kg of initial BW) were used to evaluate the effects of ractopamine-HCl (RAC) and days on feed on performance, carcass characteristics, and skeletal muscle gene expression in finishing steers. Treatment groups included serial slaughter dates of 150, 171, or 192 d on feed. Within each slaughter date, steers either received RAC (200 mg/steer) daily for the final 28 d or were not fed RAC. All steers were initially implanted with Revalor-IS and were reimplanted with Revalor-S after 75 d on feed. At slaughter, muscle samples from the semimembranosus were collected for mRNA analysis of the beta-adrenergic receptors (beta-AR). Ractopamine administration increased (P < 0.05) ADG, G:F, and HCW and increased (P = 0.08) LM area. Ractopamine did not affect the dressing percentage, USDA yield grade, or quality grade (P > 0.3). There was no change in overall feed intake across the entire feeding period; however, feed intake was increased during the 28-d period during which the steers were fed RAC (P < or = 0.05). Greater days on feed decreased (P < 0.05) ADG, G:F, DMI, and the number of yield grade 1 and 2 carcasses. Also, greater days on feed increased (P < 0.05) HCW, dressing percentage, and the number of prime and choice carcasses, as well as the number of yield grade 4 and 5 carcasses. Increasing days on feed decreased (P < 0.05) the abundance of beta(1)-AR and beta(3)-AR mRNA and increased (P < 0.05) the abundance of beta(2)-AR mRNA in skeletal muscle samples obtained at slaughter. Ractopamine had no effect (P > 0.10) on the abundance of beta(1)-AR or beta(3)-AR mRNA, but tended (P = 0.09) to increase beta(2)-AR mRNA. Additional time-course studies with primary muscle cell cultures revealed that advancing time in culture increased (P < 0.001) beta(2)-AR mRNA but had no effect (P > 0.10) on beta(1)-AR or beta(3)-AR mRNA. We conclude that days on feed and RAC are affecting beta-AR mRNA levels, which could, in turn, impact the biological response to RAC feeding in yearling steers.
选用周岁公牛（n = 2552头；初始体重314千克）来评估盐酸莱克多巴胺（RAC）以及育肥天数对育肥牛生长性能、胴体特征和骨骼肌基因表达的影响。处理组包括150天、171天或192天的连续屠宰日期。在每个屠宰日期内，公牛在育肥的最后28天要么每天接受RAC（200毫克/头），要么不饲喂RAC。所有公牛最初均植入了瑞凡洛 - IS，育肥75天后再次植入瑞凡洛 - S。屠宰时，采集半膜肌的肌肉样本用于β - 肾上腺素能受体（β - AR）的mRNA分析。饲喂莱克多巴胺使平均日增重（ADG）、料重比（G:F）和热胴体重（HCW）增加（P < 0.05），使眼肌面积（LM）增加（P = 0.08）。莱克多巴胺对屠宰率、美国农业部产量等级或质量等级没有影响（P > 0.3）。在整个育肥期内总采食量没有变化；然而，在饲喂RAC的28天期间采食量增加（P ≤ 0.05）。育肥天数增加使ADG、G:F、干物质采食量（DMI）以及1级和2级胴体数量减少（P < 0.05）。此外，育肥天数增加使HCW、屠宰率、特级和优级胴体数量以及4级和5级胴体数量增加（P < 0.05）。育肥天数增加使屠宰时采集的骨骼肌样本中β(1)-AR和β(3)-AR mRNA丰度降低（P < 0.05），使β(2)-AR mRNA丰度增加（P < 0.05）。莱克多巴胺对β(1)-AR或β(3)-AR mRNA丰度没有影响（P > 0.10），但有增加β(2)-AR mRNA的趋势（P = 0.09）。对原代肌细胞培养进行的额外时间进程研究表明，培养时间延长使β(2)-AR mRNA增加（P < 0.001），但对β(1)-AR或β(3)-AR mRNA没有影响（P > 0.10）。我们得出结论，育肥天数和RAC正在影响β - AR mRNA水平，这反过来可能会影响周岁公牛对RAC饲喂的生物学反应。
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