Evaluation of florfenicol for the treatment of undifferentiated fever in feedlot calves in western Canada.

A study was conducted in western Canada to evaluate the efficacy of florfenicol for the treatment of undifferentiated fever (UF) in feedlot calves. One hundred and twenty-five recently weaned, auction market derived, crossbred, beef steer calves suffering from UF were allocated to 1 of 2 experimental groups as follows: florfenicol, which was intramuscular florfenicol administered at the rate of 20 mg/kg body weight at the time of allocation (day 0) and again 48 h later; or control, which was intramuscular saline administered at the same volume as florfenicol at the time of allocation and again 48 h later. Eighty-four calves were allocated to the florfenicol group and 41 calves were allocated to the control group. Outcome measures describing animal health, body weight, and rectal temperature parameters were used to determine the efficacy of florfenicol for the treatment of UF. The 1st relapse of UF, 2nd relapse of UF, overall mortality, bovine respiratory disease mortality, and haemophilosis mortality rates were significantly (P < 0.05) lower in the florfenicol group than in the control group. Animals in the florfenicol group were significantly (P < 0.05) heavier at day 15 and day 45 than animals in the control group. The rectal temperature on days 1, 2, 3, and 4 of animals in the florfenicol group was significantly (P < 0.05) lower than in the control group. In addition, the change in rectal temperature from day 0 to day 4 was significantly (P < 0.05) different between the experimental groups. The results of this study demonstrate that florfenicol is an efficacious antimicrobial for the treatment of UF.