Winterholler S J, Parsons G L, Walker D K, Quinn M J, Drouillard J S, Johnson B J
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506, USA.
J Anim Sci. 2008 Sep;86(9):2401-14. doi: 10.2527/jas.2007-0482. Epub 2008 May 9.
Two experiments evaluated the effects of conventional and natural feedlot management systems (MS) on ractopamine-HCl (RAC) response in yearling steers. Feedlot performance, carcass characteristics, skeletal muscle gene expression, and circulating IGF-I concentrations were measured. The conventional system included a combined trenbolone acetate and estradiol implant, Revalor-S (IMP), as well as monensin-tylosin feed additives (IA). Treatments were arranged in a 2 x 2 factorial and included: 1) natural (NAT): no IMP-no IA, no RAC; 2) natural plus (NAT+): no IMP-no IA, RAC; 3) conventional (CON): IMP-IA, no RAC; and 4) conventional plus (CON+): IMP-IA, RAC. In Exp. 1, one hundred twenty crossbred steers (initial BW = 400 +/- 26 kg) were allotted randomly to treatment in a randomized complete block design (BW was blocking criteria); pen was the experimental unit. In Exp. 2, twenty-four individually fed crossbred steers (initial BW = 452 +/- 25 kg) were used in a randomized complete block design (BW was blocking criteria) and assigned to the same treatments as Exp. 1, with 6 steers/treatment. In Exp. 2, serum was harvested on d 0 and 31 and within the 28-d RAC feeding period, at d 0, 14, and 28. Longissimus biopsy samples were taken on d 0, 14, and 28 of the RAC feeding period for mRNA analysis of beta-adrenergic receptors and steady-state IGF-I mRNA. In Exp. 1, ADG, G:F, final BW, and HCW were greatest for CON+ (P < 0.01). During the final 37 d, RAC increased ADG (P = 0.05) and increased overall G:F (P = 0.02). Marbling score was reduced (P = 0.02), and yield grade was improved with RAC (P = 0.02), but RAC did not affect dressing percentage (P = 0.96) or HCW (P = 0.31). In Exp. 2, MS x RAC interactions were detected in ADG and G:F the last 28 d, overall ADG and overall G:F, final BW, and HCW (P < 0.01). Dressing percentage, yield grade, and marbling score were not altered by MS or RAC (P > 0.10). Circulating IGF-I concentration was increased on d 31 by the conventional MS, and concentration was greater throughout the study than NAT steers (P < 0.01). Circulating IGF-I concentrations were not changed by RAC (P = 0.49). Abundance of beta(1)-AR mRNA tended to increase (P = 0.09) with RAC, but RAC did not affect beta(2)-AR, beta(3)-AR, or IGF-I mRNA (P > 0.40). Management system did not affect beta(1)-AR, beta(2)-AR, beta(3)-AR, or IGF-I mRNA (P > 0.18), yet a trend (P = 0.06) for MS x RAC for beta(2)-AR mRNA was detected. These results indicate that response to RAC is affected by feedlot management practices.
两项试验评估了传统饲养管理系统和自然饲养管理系统对一岁公牛盐酸莱克多巴胺（RAC）反应的影响。测定了饲养场性能、胴体特征、骨骼肌基因表达和循环中胰岛素样生长因子-I（IGF-I）浓度。传统系统包括醋酸群勃龙和雌二醇复合植入剂Revalor-S（IMP）以及莫能菌素-泰乐菌素饲料添加剂（IA）。处理按2×2析因设计安排，包括：1）自然组（NAT）：无IMP-无IA，无RAC；2）自然+组（NAT+）：无IMP-无IA，RAC；3）传统组（CON）：IMP-IA，无RAC；4）传统+组（CON+）：IMP-IA，RAC。在试验1中，120头杂交公牛（初始体重=400±26千克）按随机完全区组设计随机分配至各处理组（体重为区组划分标准）；栏为试验单位。在试验2中，24头单独饲养的杂交公牛（初始体重=452±25千克）按随机完全区组设计（体重为区组划分标准）使用，并分配至与试验1相同的处理组，每组6头公牛。在试验2中，于第0天和第31天以及在28天的RAC饲喂期内的第0天、第14天和第28天采集血清。在RAC饲喂期的第0天、第14天和第28天采集背最长肌活检样本，用于β-肾上腺素能受体和稳态IGF-I mRNA的mRNA分析。在试验1中，CON+组的平均日增重（ADG）、料重比（G:F）、末重和热胴体重（HCW）最高（P<0.01）。在最后37天，RAC提高了ADG（P=0.05）并提高了总体G:F（P=0.02）。大理石花纹评分降低（P=0.02），RAC提高了产肉等级（P=0.02），但RAC不影响屠宰率（P=0.96）或HCW（P=0.31）。在试验2中，在最后28天的ADG和G:F、总体ADG和总体G:F、末重和HCW方面检测到饲养管理系统（MS）×RAC的交互作用（P<0.01）。屠宰率、产肉等级和大理石花纹评分不受MS或RAC的影响（P>0.10）。传统饲养管理系统使第31天的循环IGF-I浓度升高，且在整个研究期间其浓度均高于自然组公牛（P<0.01）。RAC未改变循环IGF-I浓度（P=0.49）。RAC使β(1)-AR mRNA丰度有增加趋势（P=0.09），但RAC不影响β(2)-AR、β(3)-AR或IGF-I mRNA（P>0.40）。饲养管理系统不影响β(1)-AR、β(2)-AR、β(3)-AR或IGF-I mRNA（P>0.18），但检测到MS×RAC对β(2)-AR mRNA有一个趋势（P=0.06）。这些结果表明，对RAC的反应受饲养场管理方式的影响。
