Antimicrobial use in sheep and antimicrobial resistance among Salmonella spp. and Escherichia coli from cull ewes in Alberta
As part of a larger sheep health surveillance project carried out in Alberta in 2001, a study was conducted examining antimicrobial resistance in enteric bacteria of ovine origin. Antimicrobial use information was collected using a flock-level questionnaire for flocks providing cull ewes to the project. Fecal contents from the ewes were cultured for 'Salmonella' spp. and generic 'Escherichia coli'. Isolates were tested for susceptibility to 18 antimicrobials using broth microdilution methodology. Antimicrobial use appeared to be relatively infrequent in the Alberta sheep industry. Ninety-seven percent of 'Salmonella' isolates (mainly ' S. enterica' subspecies 'diarizonae') and 66% of generic ' E. coli' were susceptible to all 18 antimicrobials. Logistic regression was used to identify risk factors that were statistically associated with the occurrence of antimicrobial resistance in generic 'E. coli' isolates. These included flock size, antimicrobial use for prophylaxis and/or group therapy, in-feed antimicrobial use and the use of specific antimicrobials.