Health and feed performance parameters of 293 beef stocker calves at risk for bovine respiratory disease were compared after metaphylactic administration of one of two antimicrobials (tulathromycin or tilmicosin) with different durations of activity; the antimicrobial was administered 1 day after arrival. Calves that received metaphylactic tulathromycin displayed significant improvement in morbidity, mortality, and first-treatment success rates (P<.05) compared with tilmicosin-treated calves. Tulathromycin-treated calves also showed a significantly improved average daily gain and feed:gain ratio (P<.05) compared with tilmicosin-treated calves. Under conditions of this study, calves receiving tulathromycin were healthier through a 43-day growing phase compared with calves receiving tilmicosin. This health difference likely accounted for the differences in feed performance between the treatment groups.