Two replicated-pen field studies were performed under commercial feedlot conditions in western Canada to compare the administration of long-acting
oxytetracycline at 30 mg/kg
body weight (BW) versus
tilmicosin at 10 mg/kg BW to feedlot calves upon arrival at the feedlot. Ten thousand nine hundred and eighty-nine, recently weaned, auction market derived, crossbred beef steer and bull calves were randomly allocated upon arrival at the feedlot to one of 2 experimental groups as follows:
oxytetracycline, which received intramuscular long-acting
oxytetracycline (300 mg/mL formulation) at a rate of 30 mg/kg BW; or
tilmicosin, which received subcutaneous
tilmicosin (300 mg/mL formulation) at a rate of 10 mg/kg BW. There were 20 pens in each experimental group. In Study 1 and in the combined analysis, the initial undifferentiated
fever (UF) treatment rate was significantly (P < 0.05) higher in the
oxytetracycline group as compared with the
tilmicosin group. There were no significant (P > or = 0.05) differences in first UF relapse, second UF relapse, third UF relapse, overall chronicity, overall rail, overall mortality, bovine respiratory disease (BRD) mortality, hemophilosis mortality,
arthritis mortality, or miscellaneous mortality rates between the experimental groups in either study or in the combined analysis. In addition, there were no significant (P > or = 0.05) differences in initial weight, final weight,
weight gain, days on feed, daily dry matter intake, average daily gain, or the dry matter intake to gain ratio between the experimental groups in either study or in the combined analyses. In the economic analysis, there was a net economic advantage of $5.22 CDN per animal in the
oxytetracycline group, due to a lower prophylactic cost, even though the UF therapeutic cost was higher.