Antimicrobial use and resistance in fecal Escherichia coli from Canadian pigs at the beginning and end of finishing

The objectives of this thesis were to determine: the prevalence of antimicrobial resistance (AMR) in fecal Escherichia coli isolated from samples collected from pens of pigs arriving in the grower-finisher unit and again from the same pens at close-to-market (CTM) weight; the change in prevalence of AMR in these two age groups; the prevalence of antimicrobial use (AMU) in grower-finisher pigs; and to evaluate the associations between the prevalence of AMR at arrival and CTM.;Of the 15 antimicrobials, the highest adjusted prevalence of resistance in arrival (100.0%) and CTM (93.5%) isolates was for tetracycline. Arrival isolates had significantly higher odds of resistance to chloramphenicol, sulfisoxazole, streptomycin, trimethoprim-sulfamethoxazole and tetracycline than CTM isolates. Twenty-one of the 28 herds submitted AMU data and all used antimicrobials through at least one route, most commonly macrolides. Antimicrobial resistance at arrival was significantly (P < 0.05) associated with kanamycin and trimethoprim-sulfamethoxazole CTM resistance and a confounder for the relationship between the use of medicated water and streptomycin resistance at CTM.