Hagenmaier J A, Reinhardt C D, Ritter M J, Calvo-Lorenzo M S, Vogel G J, Guthrie C A, Siemens M G, Lechtenberg K F, Rezac D J, Thomson D U
J Anim Sci. 2017 May;95(5):1977-1992. doi: 10.2527/jas.2016.0936.
Feedlot cattle ( = 128; BW = 549 ± 60 kg) were used to evaluate the effects of ractopamine hydrochloride (RAC) on growth performance, physiological response to handling, and mobility during shipment for slaughter in a study utilizing a split-plot design with a 2 × 2 factorial arrangement of treatments: 1) diet (CON [no β-adrenergic agonist] vs. RAC [400 mg·animal·d ractopamine hydrochloride for 28 d]) and 2) handling intensity (HI; low-stress handling [LSH; cattle moved at a walking pace with no electric prod use] vs. high-stress handling [HSH; cattle moved at a minimum of a trot and an electric prod applied while in the alley for posthandling restraint and during loading for shipment to the abattoir]). Cattle fed RAC tended to have greater ADG and G:F ( = 0.06), and had greater HCW and LM area ( = 0.04). The HI treatments were applied on the day after the 28-d growth performance period. Blood samples were collected before HI treatment (baseline), after HI treatments (POSTHAND), after transport to the abattoir (POSTTRANS), and during exsanguination at slaughter. A diet × HI interaction ( = 0.01) was observed in the change in cortisol from baseline to POSTTRANS, and there tended ( ≤ 0.07) to be diet × HI interactions for the change in epinephrine from baseline to POSTHAND and for the change in creatine kinase (CK) from baseline to POSTTRANS. Feeding RAC and HSH both increased the change from baseline to POSTHAND in norepinephrine and pH ( ≤ 0.05). The HSH cattle also had greater changes from baseline to POSTHAND in blood HCO, base excess, partial pressure of CO, lactate, cortisol, and glucose ( ≤ 0.01). Ractopamine and HSH both produced greater increases in CK concentrations from baseline to slaughter ( < 0.01). Mobility was not affected by RAC at the feedlot or following an average 6-h lairage ( ≥ 0.43). This study confirms RAC improves growth performance and suggests metabolic acidosis, a precursor to fatigued cattle syndrome, develops in cattle allowed to trot without the use of a lead rider regardless of RAC administration. Cattle fed RAC displayed altered hormonal responses to handling and transport stress, and the overall proportion of cattle with compromised mobility appears to increase later in the marketing channel. These findings warrant additional research aimed at better understanding the physiological response to stress and protect the welfare of cattle during shipment for slaughter.
在一项采用裂区设计、2×2析因处理安排的研究中，育肥牛（n = 128；体重 = 549±60千克）用于评估盐酸莱克多巴胺（RAC）对生长性能、处理时的生理反应以及屠宰运输过程中移动性的影响。处理因素如下：1）日粮（对照[无β-肾上腺素能激动剂]与RAC[28天内每头动物每天饲喂400毫克盐酸莱克多巴胺]）和2）处理强度（HI；低应激处理[LSH；牛以步行速度移动，不使用电刺激棒]与高应激处理[HSH；牛至少以小跑速度移动，在通道中进行处理后约束以及装载运往屠宰场时使用电刺激棒]）。饲喂RAC的牛倾向于具有更高的平均日增重和料重比（P = 0.06），并且具有更大的胴体重和腰大肌面积（P = 0.04）。HI处理在28天生长性能期后的第二天进行。在HI处理前（基线）、HI处理后（处理后）、运输到屠宰场后（运输后）以及屠宰放血期间采集血样。从基线到运输后的皮质醇变化中观察到日粮×HI交互作用（P = 0.01），从基线到处理后的肾上腺素变化以及从基线到运输后的肌酸激酶（CK）变化存在日粮×HI交互作用的趋势（P≤0.07）。饲喂RAC和HSH均增加了从基线到处理后去甲肾上腺素和pH的变化（P≤0.05）。HSH牛从基线到处理后的血液碳酸氢根、碱剩余、二氧化碳分压、乳酸、皮质醇和葡萄糖变化也更大（P≤0.01）。从基线到屠宰，莱克多巴胺和HSH均使CK浓度有更大增加（P<0.01）。在育肥场时或平均6小时候宰期后，RAC对移动性没有影响（P≥0.43）。本研究证实RAC可提高生长性能，并表明疲劳牛综合征的前兆代谢性酸中毒在不使用领跑员而允许小跑移动的牛中出现，无论是否给予RAC。饲喂RAC的牛对处理和运输应激的激素反应发生改变，并且在销售渠道后期，行动不便的牛的总体比例似乎会增加。这些发现需要进一步研究，以更好地了解对应激的生理反应，并在屠宰运输过程中保护牛的福利。
