When loads of stressed, high-risk calves arrive at the feedlot, it often makes economic sense to treat them all with antibiotics to prevent an almost-inevitable outbreak of bovine respiratory disease (BRD). It might also make sense from a biological standpoint.
But as pressures mount for livestock producers to reduce their use of antibiotics, using diagnostic tools to implement more limited and targeted arrival treatments potentially could reduce costs and improve outcomes. Maybe.
During the recent AABP Conference, several presentations outlined various aspects of metaphylaxis in cattle feedyards. In a previous article, we summarized a discussion of the epidemiological justification for metaphylaxis from Brian Vander Ley, DVM, PhD, an epidemiologist at the Great Plains Veterinary Education Center. In a follow-up presentation, Vander Ley discusses some of the potential benefits and challenges in incorporating diagnostics into on-arrival treatment decisions.
In theory, chute-side diagnostic tools such as blood tests or electronic auscultation can predict individual BRD risk, guide treatment decisions and possibly classify pathogens and even their sensitivity to specific antibiotics. On the downside, Vander Ley says diagnostics could slow processing speeds, add new costs and complexity and not necessarily improve clinical outcomes.
A targeted metaphylaxis program ideally would treat stressed, immune-challenged calves that are most susceptible to or infected with BRD pathogens, while not treating those already recovered from BRD, under little stressed and/or with robust immunity and little stress. In reality though, evaluating all the risk factors on individual animals presents a significant challenge.
Vander Ley notes that leaving any infected calves untreated can favor reproduction and shedding of BRD pathogens and lead to outbreaks. On the other hand, treating non-infected calves could extend the risk period by leaving those animals susceptible and exposed to pathogens after the post-metaphylactic interval (PMI).
Diagnostic tools have good potential for improving receiving programs, metaphylaxis and antibiotic stewardship, but Vander Ley stresses that in the meantime, the industry can best address BRD risk with calf management and procurement practices designed to maximize immunity, rather than fixing earlier management deficiencies with treatments on arrival.
For more on aspects of metaphylaxis decisions, see these articles from BovineVet Online: