Field study of the comparative efficacy of gamithromycin and tulathromycin for the treatment of undifferentiated bovine respiratory disease complex in beef feedlot calves

Objective-To compare the efficacy of gamithromycin with that of tulathromycin for the treatment of undifferentiated bovine respiratory disease complex (BRDC) in feedlot calves. Animals-1,049 weaned crossbred beef calves. Procedures-At each of 6 feedlots, newly arrived calves with BRDC were administered a single dose of gamithromycin (6.0 mg/kg, Sc; n = 523) or tulathromycin (2.5 mg/kg, Sc; 526). Case-fatality and BRDC retreatment rates during the first 120 days after treatment, final body weight, and average daily gain (ADG), were compared between treatments. At 2 feedlots, calves were assigned clinical scores for 10 days after treatment to determine recovery rates for each treatment. Bioequivalence limits for gamithromycin and tulathromycin were calculated for outcomes for which there was no significant difference between treatments. Results-Mean BRDC retreatment rate (177%) for calves administered gamithromycin was greater than that (9.0%) for calves administered tulathromycin. Mean case-fatality rate, final body weight, ADG, and clinical score 10 days after treatment did not differ significantly between treatments. Limits for mean differences within which gamithromycin was bio-equivalent to tulathromycin were +/- 2.4% for case-fatality rate, +/- 13 kg for final body weight, and +/- 0.1 kg/d for ADG. Conclusions and Clinical Relevance-Calves administered gamithromycin had a higher BRDC retreatment rate than did calves administered tulathromycin; otherwise, the clinical efficacy did not differ between the 2 treatments for the treatment of BRDC in feedlot calves. (Am J Vet Res 2013;74:847-853)