A comparison of florfenicol and tilmicosin for the treatment of undifferentiated fever in feedlot calves in western Canada

A field trial was performed under commercial feedlot conditions in western Canada to compare the efficacy of florfenicol and tilmicosin for the treatm ent of undifferentiated fever (UF) in calves that received metaphylactic ti lmicosin upon arrival at the feedlot. One thousand and eighty recently wean ed, auction market derived, crossbred beef calves suffering from UF were al located to one of 2 experimental groups as follows: florfenicol, which was intramuscular (IM) florfenicol administered at the rate of 20 mg/kg body we ight (BW) at the time of allocation (Day 0) and again 48 h later, or tilmic osin, which was subcutaneous (SC) tilmicosin administered once at the rate of 10 mg/kg BW on day 0. Five hundred and forty-four animals were allocated to the florfenicol group and 536 animals were allocated to the tilmicosin group. The chronicity, wastage, overall mortality, and bovine respiratory disease (BRD) mortality rates were significantly (P < 0.05) lower in the florfenico l group than in the tilmicosin group. There were no significant (P greater than or equal to 0.05) differences in first UF relapse, second UF relapse, hemophilosis mortality, or miscellaneous mortality rates between the florfe nicol and tilmicosin groups. Average daily gain (ADG) from arrival at the feedlot to the time of implant ing and ADG from allocation to the time of implanting were significantly (P < 0.05) lower in the florfenicol group as compared with the tilmicosin gro up. There were no significant (P 2 0.05) differences in arrival weight, all ocation weight, implanting weight, or ADG from arrival to allocation betwee n the experimental groups. In the economic analysis, there was an advantage of $18.83 CDN per animal in the florfenicol group. The results of this stu dy indicate that florfenicol is superior to tilmicosin for the treatment of UF because of lower chronicity, wastage, overall mortality, and BRD mortal ity rates. However, interpretation of these observations must take into con sideration the fact that these calves received metaphylactic tilmicosin upo n arrival at the feedlot, which is a standard, cost-effective, management p rocedure utilized by feedlots in western Canada.