牛呼吸道疾病(BRD)已被确定为澳大利亚东部饲养场牛最重要的传染病。1牛呼吸道疾病由于药物费用而造成经济损失,死亡率,与饲料时间增加相关的过多饲料输入,降低销售价格和相关劳动力成本。牛呼吸道疾病是一种复杂的多因素疾病,具有多种动物,环境和管理风险因素诱发牛病。BRD中涉及一系列微生物,通常单独或组合涉及至少四种病毒和五种细菌物种。在澳大利亚,与BRD最常见的病毒是牛疱疹病毒1(BHV1),牛病毒性腹泻病毒(BVDV或牛瘟病毒),牛副流感病毒3(PI3)和牛呼吸道合胞病毒(BRSV)。最近,牛冠状病毒已被确定为澳大利亚BRD的潜在病毒贡献者。2许多细菌物种也被认为对BRD复合体很重要;这些包括溶血曼海姆菌,多杀性巴氏杆菌,嗜血杆菌,化脓性真菌类和牛支原体。尽管上面列出的一种或多种病原体可以从BRD的临床病例中分离出来,没有证据表明单独感染会导致严重疾病。这表明,除了特定的传染因子,其他因素对野外条件下BRD的发展至关重要。这些可以归类为环境,动物和管理风险因素。这些危险因素可能通过多种途径发挥作用,包括降低全身免疫和可能的局部免疫。例如,压力源,如断奶,在营业厅处理,运输,脱水,天气条件,饮食变化,配伍和笔竞争可能会降低免疫系统的有效性。降低的免疫能力可以允许下气道的机会性感染,潜在的病原体导致BRD的发展。本文的目的是批判性地审查旨在减少澳大利亚饲养场牛BRD发生率的管理实践的证据。诱发因素(表1)在很大程度上超出了大多数饲养场的控制范围,比如天气和呼吸道病毒的暴露,分别讨论,但是这些因素可以产生间接预防对策,这些对策在预防实践类别下进行讨论。目前的做法分为动物准备做法(表2)或饲养场管理做法(表3)。
Bovine respiratory disease (BRD) has been identified as the most significant infectious disease of feedlot cattle in eastern Australia.1 Bovine respiratory disease causes economic loss due to medication costs, mortalities, excessive feed inputs associated with increased time on feed, reduced sale prices and associated labour costs. Bovine respiratory disease is a complex multifactorial condition with multiple animal, environmental and management risk factors predisposing cattle to illness. A range of microorganisms are implicated in BRD with at least four viral and five bacterial species commonly involved individually or in combination. The viruses most commonly associated with BRD in Australia are bovine herpesvirus 1 (BHV1), bovine viral diarrhoea virus (BVDV or bovine pestivirus), bovine parainfluenza 3 virus (PI3) and bovine respiratory syncytial virus (BRSV). More recently, bovine coronavirus has been identified as a potential viral contributor to BRD in Australia.2 A number of bacterial species have also been recognised as important to the BRD complex; these include Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Trueperella pyogenes and Mycoplasma bovis. Although one or more of the pathogens listed above can be isolated from clinical cases of BRD, there is no evidence that infection alone causes serious illness. This indicates that, in addition to specific infectious agents, other factors are crucial for the development of BRD under field conditions. These can be categorised as environmental, animal and management risk factors. These risk factors are likely to exert their effects through multiple pathways including reductions in systemic and possibly local immunity. For example, stressors such as weaning, handling at saleyards, transport, dehydration, weather conditions, dietary changes, comingling and pen competition might reduce the effectiveness of the immune system. Reduced immunocompetence can allow opportunistic infection of the lower airways with potential pathogens leading to the development of BRD. The objective of this paper is to critically review the evidence for management practices aimed at reducing the incidence of BRD in Australian feedlot cattle. Predisposing factors (Table 1) largely beyond the control of most feedlots, such as weather and exposure to respiratory viruses, are discussed separately, but these factors can generate indirect prevention responses that are discussed under the preventative practices categories. The current practices are classified as either animal preparation practices (Table 2) or feedlot management practices (Table 3).