This thesis summarizes an investigation of antimicrobial resistance (AMR) and antimicrobial use (AMU) in cow-calf herds. The specific objectives of this project were to describe common reasons for treatment and the types of antimicrobials used in cow-calf herds, to describe the frequency of AMR in generic fecal Escherichia coli isolated from various age groups commonly found on cow-calf farms, to determine risk factors associated with the occurrence of AMR, and finally to investigate the underlying molecular mechanisms of AMR in cow-calf herds. At least 86% of the herds treated one or more calves or cows during the study period; however, the overall proportion of both calves and cows reported as treated was less than 14% for calves and 3% for cows. The majority of antimicrobials reported as used in cow-calf operations were for individual therapeutic use rather than prophylaxis, metaphylaxis, or growth promotion. Injectable formulations were the most commonly reported method of antimicrobial administration on cow-calf farms. Cow-calf herds in Wetern Canada are not a significant reservoir for resistance to antimicrobials classified as very important to human medicine such as ciprofloxacin and ceftiofur. The three most common resistances detected were to tetracycline, sulphamethoxazole, and streptomycin regardless of age group. Young calves sampled in the spring of the year were more likely to be shedding AMR E. coli than older calves sampled in the fall of the year or than cows sampled in the spring of the year. The cow-calf pair relationship was not an important factor in transfer of AMR from the individual cow to her calf, but the presence of AMR in the general cow herd was associated with AMR in the calf population. The potential importance of co-selection for AMR at the molecular level was demonstrated by both the risk factor analysis and the molecular work. Phenotypic resistance to streptomycin, tetracycline, and sulphamethoxazole were each associated with the presence of resistance genes from all six families of antimicrobials examined in this study. Several statistically significant associations were also detected between the resistance genes considered. No significant associations were detected between any of the AMR phenotypes or genotypes and the STEC virulence factors stx1, stx2 and eae.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:SSU.etd-09182007-154755 |
| Date | 19 September 2007 |
| Creators | Gow, Sheryl Pamela |
| Contributors | Polley, Lydden, Dowling, Patricia M., Dargatz, Dave, Carruthers, Terry D., Campbell, John R., Waldner, Cheryl |
| Publisher | University of Saskatchewan |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-09182007-154755/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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