Context There is pressure on production veterinarians to reduce the use of antibiotics in intensive beef production systems. Aims The present study investigated whether preconditioning – the process whereby weaned calves destined for the feedlot are prepared over a period of time – reduced antibiotic treatment events, and improved health and production of calves in a South African feedlot. Methods Preconditioned calves (n = 301) and control calves (n = 332) were sourced from the same origin on two occasions, and arrived at the feedlot on the same day. Bovine respiratory disease (BRD) was defined as the ‘pulling’ of clinically sick calves from feedlot pens, followed by the standard protocol for treatment of BRD (including antibiotic treatment). Outcome variables related to health were BRD overall incidence (pulling), BRD re-pulling and lung lesion scores. Production outcome variables measured were carcass weight, carcass average daily gain (ADG) and days on feed (DOF). Initial carcass weight was estimated from shrunk liveweight in order to estimate the effect of preconditioning on carcass gain, the most economically relevant outcome. Statistical analyses were done using multiple linear, logistic and Cox regression. Predictor variables were preconditioning vs control, gender, starting weight, DOF, pulling for BRD and carcass ADG. Key results A lower proportion of preconditioned calves were pulled and a lower proportion of pulled calves were re-pulled for BRD compared with control calves (8 vs 17% and 8 vs 16%, respectively, P < 0.01). A higher proportion of preconditioned calves compared with control calves were market ready at 90 DOF (89 vs 67%, P < 0.01). In the multivariable models preconditioning was associated with a 200 g/d increase in carcass growth rate (P < 0.01) and with a 17.7 kg increase in overall carcass gain (P < 0.01) after adjusting for gender and DOF. Conclusions Preconditioning reduced the incidence and severity of BRD and feedlot standing time and improved production of calves in South African feedlots. Implications Preconditioning has the potential to add value to the beef feedlot by reducing the formation of antimicrobial resistance while improving the profitability of the feedlot.

中文翻译：

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南非牛肉饲养场预处理对生产和抗生素使用的影响

背景 生产兽医面临着减少在集约化牛肉生产系统中使用抗生素的压力。目的 本研究调查了预处理——在一段时间内准备送往饲养场的断奶小牛的过程——是否减少了抗生素治疗事件，并改善了南非饲养场中犊牛的健康和生产。方法预处理犊牛（n = 301）和对照犊牛（n = 332）两次来自同一来源，并在同一天到达饲养场。牛呼吸系统疾病 (BRD) 被定义为将临床病牛从饲养栏“拉出”，然后按照标准的 BRD 治疗方案（包括抗生素治疗）进行治疗。与健康相关的结果变量是 BRD 总体发生率（拉动），BRD 再牵拉和肺损伤评分。测量的生产结果变量是胴体重、胴平均日增重 (ADG) 和饲料天数 (DOF)。初始胴体重是根据收缩的活重估计的，以估计预处理对胴体重的影响，这是最经济相关的结果。使用多元线性、logistic 和 Cox 回归进行统计分析。预测变量是预处理与对照、性别、起始重量、自由度、BRD 和胴体 ADG 的拉力。主要结果 与对照犊牛相比，为了 BRD 牵拉的预处理犊牛比例较低，再牵拉的犊牛比例较低（分别为 8 对 17% 和 8 对 16%，P < 0.01）。与对照犊牛相比，更高比例的预处理犊牛在 90 DOF 时已做好上市准备（89 对 67%，P < 0。01)。在多变量模型中，在调整性别和自由度后，预处理与胴体生长率增加 200 g/d (P < 0.01) 和总体胴体生长增加 17.7 kg (P < 0.01) 相关。结论 预处理降低了 BRD 的发生率和严重程度以及饲养场站立时间，并提高了南非饲养场的犊牛产量。影响 预处理有可能通过减少抗菌素耐药性的形成同时提高饲养场的盈利能力来增加牛肉饲养场的价值。结论 预处理降低了 BRD 的发生率和严重程度以及饲养场站立时间，并提高了南非饲养场的犊牛产量。影响 预处理有可能通过减少抗菌素耐药性的形成同时提高饲养场的盈利能力来增加牛肉饲养场的价值。结论 预处理降低了 BRD 的发生率和严重程度以及饲养场站立时间，并提高了南非饲养场的犊牛产量。影响 预处理有可能通过减少抗菌素耐药性的形成同时提高饲养场的盈利能力来增加牛肉饲养场的价值。