The efficacy of tulathromycin in decreasing the incidence of morbidity and mortality due to bovine respiratory disease (BRD) in 1,239 high-risk cattle was investigated at four US feedlots. Calves not exhibiting clinical signs of BRD received one of three treatments administered SC in the neck: physiologic saline at 0.02 ml/kg, tulathromycin at 2.5 mg/kg, or tilmicosin at 10 mg/kg. Each treatment group consisted of 413 calves. Calves with clinical signs of BRD and rectal temperatures of 104 degrees F or higher on any day through day 14 were considered treatment failures (BRD morbidity). Nasopharyngeal swabs from saline-treated morbidities were submitted for isolation and identification of BIRD organisms. Respiratory disease morbidity was highest in calves treated with saline and significantly (P <= .0001) lower in calves that received tulathromycin or tilmicosin. Morbidity from BRD was significantly (P <= .0001) higher in calves treated with tilmicosin than in calves treated with tulathromycin. Under conditions of this study, tulathromycin given to calves at high risk of developing BRD was significantly more effective in reducing BRD morbidity compared with both saline and tilmicosin.

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 (2.5 mg/kg SC) or enrofloxacin (12.5 mg/kg SC). Additional the apy 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.