•   Tulathromycin is a macrolide antibiotic used to treat bovine respiratory disease (BRD) in cattle and swine respiratory disease in pigs.

•   Clinical effectiveness of tulathromycin 217500-96-4, a novel triamilide antimicrobial, for the control of respiratory disease in cattle at high risk for developing bovine respiratory disease.

    The efficacy of tulathromycin 217500-96-4 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 subcutaneously in the neck: physiologic saline at 0.02 ml/kg, tulathromycin 217500-96-4 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 days 1 through 14 were considered treatment failures (BRD morbidity). Nasopharyngeal swabs from saline-treated morbidities were submitted for isolation and identification of BRD organisms. Respiratory disease morbidity was highest in calves treated with saline and significantly (P < or = .0001) lower in calves administered tulathromycin 217500-96-4 or tilmicosin. Morbidity from BRD was significantly (P < or = .0001) higher in calves treated with tilmicosin than in calves treated with tulathromycin 217500-96-4. Under conditions of this study, tulathromycin 217500-96-4, given to calves at high risk of developing BRD, was significantly more effective in reducing BRD morbidity when compared to both saline- and tilmicosin-treated calves.