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The purpose of this study was to compare the efficacy and cost-effectiveness of florfenicol versus tulathromycin for initial treatment of undifferentiated fever in fallplaced steer calves that received metaphylactic tilmicosin on arrival at the feedlot. No significant differences (P > .10) were observed in undifferentiated fever relapses or the crude case fatality rate. Calves treated with florfenicol had a lower case fatality rate (P = .04) for bovine respiratory disease and Histophilus disease than did calves treated with tulathromycin. The net economic advantage of florfenicol over tulathromycin (Can$17.70/treated animal) was based on differences in costs for the trial drug and calf replacement owing to bovine respiratory disease and Histophilus disease case fatality.

Undifferentiated fever (UF), also known as bovine respiratory disease (BRD), is a common clinical disease in Canadian feedlot cattle. The term UF, which is commonly used in Alberta feedlots, has been described previously.Prevention, control, and treatment of UF involve the use of various respiratory vaccines and the administration of antimicrobials, either parenterally or orally. High-risk fall-placed feedlot calves are given long-acting metaphylactic antimicrobials (e.g., long-acting oxytetracycline, tilmicosin, tulathromycin) during onarrival processing to reduce disease rates and improve performance.