Efficacy of tulathromycin or enrofloxacin for initial treatment of naturally occurring bovine respiratory disease in feeder calves.

After undergoing arrival processing at one of two commercial feedlots, feeder calves with clinical signs of bovine respiratory disease (BRD) were randomly assigned to receive either tulathromycin (2.4 mg/kg SC) or enrofloxacin (12.5 mg/kg SC). Additional therapy for calves that did not respond to initial treatment followed a prescribed course. Initial treatment with tulathromycin resulted in significantly higher (P = .009 and P = .031 at sites 1 and 2, respectively) therapeutic success (87.9% and 80%, respectively) than did initial treatment with enrofloxacin (70.2% and 62.5%, respectively). Animals treated with tulathromycin also had fewer subsequent treatments and higher weight gains compared with those treated with enrofloxacin.