Abney C S, Vasconcelos J T, McMeniman J P, Keyser S A, Wilson K R, Vogel G J, Galyean M L
Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409-2141, USA.
J Anim Sci. 2007 Nov;85(11):3090-8. doi: 10.2527/jas.2007-0263. Epub 2007 Jul 3.
Two experiments evaluated effects of ractopamine hydrochloride (RAC) on performance, intake patterns, and acid-base balance of feedlot cattle. In Exp. 1, 360 crossbred steers (Brangus, British, and British x Continental breeding; initial BW = 545 kg) were used in a study with a 3 x 3 factorial design to study the effects of dose [0, 100, or 200 mg/(steer x d) of RAC] and duration (28, 35, or 42 d) of feeding of RAC in a randomized complete block design (9 treatments, 8 pens/treatment). No dose x duration interactions were detected (P > 0.10). As RAC dose increased, final BW (FBW; P = 0.01), ADG (P < 0.01), and G:F (P < 0.01) increased linearly. As duration of feeding increased, ADG increased quadratically (P = 0.04), with tendencies for quadratic effects for FBW (P = 0.06), DMI (P = 0.07), and G:F (P = 0.09). Hot carcass weight increased linearly (P = 0.02) as dose of RAC increased. Thus, increasing the dose of RAC from 0 to 200 mg/(steer x d) and the duration of feeding from 28 to 42 d improved feedlot performance, although quadratic responses for duration of feeding indicated little improvement as the duration was extended from 35 to 42 d. In Exp. 2, 12 crossbred beef steers (BW = 593 kg) were used in a completely random design to evaluate the effects of RAC [0 or 200 mg/(steer x d) for 30 d; 6 steers/treatment] on rate of intake, daily variation in intake patterns, and acid-base balance. To assess intake patterns, absolute values of daily deviations in feed delivered to each steer relative to the total quantity of feed delivered were analyzed as repeated measures. There were no differences (P > 0.10) in feedlot performance, urine pH, blood gas measurements, or variation in intake patterns between RAC and control cattle, but steers fed RAC had increased (P = 0.04) LM area, decreased (P = 0.03) yield grade, and increased (P < 0.10) time to consume 50 and 75% of daily intake relative to control steers. Our results suggest that feeding RAC for 35 d at 200 mg/(steer x d) provided optimal performance, and no effects on acid-base balance or variation in intake patterns of finishing steers were noted with RAC fed at 200 mg/(steer x d) over a 30-d period.
两项试验评估了盐酸莱克多巴胺（RAC）对育肥牛生长性能、采食模式及酸碱平衡的影响。在试验1中，选用360头杂交阉牛（布拉斯、英国品种以及英国与欧洲大陆品种杂交；初始体重=545千克），采用3×3析因设计，以随机完全区组设计（9种处理，每种处理8个圈舍）研究RAC剂量[0、100或200毫克/（头·天）]和饲喂时间（28、35或42天）的影响。未检测到剂量×时间的交互作用（P>0.10）。随着RAC剂量增加，末重（FBW；P=0.01）、平均日增重（ADG；P<0.01）和料重比（G:F；P<0.01）呈线性增加。随着饲喂时间延长，ADG呈二次曲线增加（P=0.04），FBW（P=0.06）、干物质采食量（DMI；P=0.07）和G:F（P=0.09）有二次效应趋势。热胴体重随RAC剂量增加呈线性增加（P=0.02）。因此，将RAC剂量从0增加到200毫克/（头·天）以及将饲喂时间从28天延长到42天可提高育肥牛生长性能，尽管饲喂时间的二次反应表明从35天延长到42天改善不大。在试验2中，选用12头杂交肉牛阉牛（体重=593千克），采用完全随机设计，评估RAC[0或200毫克/（头·天），持续30天；每种处理6头牛]对采食速度、采食模式的日变化及酸碱平衡的影响。为评估采食模式，将每头牛实际采食饲料量相对于总供给量的每日偏差绝对值作为重复测量指标进行分析。RAC组与对照组在育肥牛生长性能、尿液pH值、血气指标或采食模式变化方面无差异（P>0.10），但饲喂RAC的阉牛的腰大肌面积增加（P=0.04），产肉等级降低（P=0.03），相对于对照阉牛，采食50%和75%日采食量所需时间增加（P<0.10）。我们的结果表明，以200毫克/（头·天）的剂量饲喂RAC 35天可获得最佳生长性能，在30天的时间里，以200毫克/（头·天）的剂量饲喂RAC对育肥牛的酸碱平衡或采食模式变化无影响。
