Diagnostic Considerations for Bovine Respiratory Disease

Bovine respiratory disease remains a significant cause of economic loss to the cattle industry1 and source of frustration to the cow/calf sector, the feedlot industry, veterinary practitioners and laboratory diagnosticians. Numerous contributing factors are involved including weaning stress, shipping, commingling, anatomic and physiologic features of the bovine respiratory tract and multiple infectious agents. The role of many of these agents is currently not fully understood. This has led to the term bovine respiratory disease complex (BRD).2 BRD can be a clinically useful term but to the laboratory diagnostician and the practitioner trying to design a control program or a treatment regimen a more specific etiologic diagnosis is generally necessary. While numerous infectious agents have been reported to be involved in the BRD complex only a handful appear to be of major etiologic significance (Table 1). Identifying the specific risk factor(s) and agent(s) involved in a particular group of cattle best involves a team approach and this includes feedlot management and personnel, on-site and consulting veterinarians and diagnostic laboratory personnel. Good communication between field veterinarian and the diagnostic laboratory are particularly critical as is an understanding by field veterinarians of the limitations of the various laboratory tests. Early identification and treatment of sick animals is considered to be the key to success in outbreaks of BRD and early, accurate diagnosis is prerequisite to successful treatment. The inherent time lag in many laboratory tests necessitates that the practitioner often has to act on their initial clinical impression but laboratory confirmation and monitoring can be essential to adjusting treatment and preventative protocols.