Tulathromycin metaphylaxis increases prevalence of multidrug resistant Mannheimia haemolytica while improving health in stocker calves

Bovine respiratory disease (BRD) is commonly controlled by metaphylaxis, but increasing prevalence of antimicrobial re­sistant (AMR) Mannheimia haemolytica (MH) may decrease ef­ficacy. The objective of this study was to determine the effect of macrolide metaphylaxis on 1) morbidity and mortality in stocker cattle over a 21-day period and 2) isolation rate and anti­microbial susceptibility of MH at arrival (d0) and d21.