Efficacy of antimicrobial treatment for bovine respiratory disease: a systematic review and meta-analysis for European Network for Optimization of Veterinary Antimicrobial Therapy guidelines

<ns3:p> Bovine respiratory disease (BRD) is a leading cause of illness and death in cattle and a major driver of antimicrobial use. This systematic review and meta-analysis assessed the clinical effectiveness of five commonly used antimicrobial classes (penicillins, tetracyclines, phenicols, macrolides, and fluoroquinolones) in the treatment of cattle with natural BRD. Cattle from all production systems (feedlot, dairy, slaughter, and stocker) were included, and metaphylaxis trials were excluded. Peer-reviewed trials were searched in several databases, and all reports were screened in duplicate for data extraction and risk of bias. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) methodology was employed to evaluate the certainty of evidence. Twenty-eight randomized controlled trials were included. We did not detect clinically meaningful differences between antimicrobial classes in reducing the need for re-treatment (a surrogate for short-term therapeutic failure). Certainty of evidence ranged from very low to moderate, and results should be interpreted cautiously. Subgroup estimates were broadly consistent for production systems (feedlot and non-feedlot) and for trials with <ns3:italic>Mycoplasma</ns3:italic> -positive animals; however, these subgroup analyses were small and imprecise and do not allow firm conclusions. Mortality, relapse, and growth outcomes were measured inconsistently and could not be reliably pooled. Overall, we did not identify any class with a clinically meaningful short-term advantage based on our prespecified thresholds. The results of this systematic review and meta-analysis will inform the BRD Antimicrobial Use Guidelines of the European Network for Optimization of Antimicrobial Therapy (ENOVAT). </ns3:p>