ANTI-MICROBIAL USE IN FEEDLOT CALVES - ITS ASSOCIATION WITH CULTURE RATES AND ANTI-MICROBIAL SUSCEPTIBILITY

Abstract

Use of antimicrobial agents and health problems was studied in beef feedlot calves. Although the association between them was not significant, many feedlot owners did not use recommended dosages or duration of treatment; this may have led to a reduced recovery rate. Injectable tetracyclines were the most frequently chosen antimicrobial for primary treatment of sick calves; chloramphenicol was selected most frequently when the primary treatment appeared to be ineffective. Treatment with antimicrobials reduced the likelihood of isolating Pasteurella multocida and Haemophilus somnus. Chloramphenicol therapy reduced the likelihood of isolating P. haemolytica. Therapy with a particular antimicrobial in the week prior to death increased the level of resistance in P. haemolytica to that antimicrobial. Treatment with other antimicrobials also increased the level of resistance to that antimicrobial, although to a lesser degree. The lowest levels of resistance were observed in Pasteurella isolated from nontreated cattle. After adjustment for antimicrobial exposure, resistance to penicillin, tetracyclines and chloramphenicol occurred together more frequently than expected by chance alone.