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Agent-based modeling to address emerging threats from antimicrobial resistance to the sustainability of the beef industry



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Antimicrobial resistance (AMR) is a global public health concern for both human and animal health. The rise in AMR has led to increased scrutiny of antimicrobial use (AMU) in feedlot cattle. With rising concern for prudent AMU in the beef industry, it is essential to understand the potential impact of eliminating parenteral metaphylaxis on AMR and animal health. Further, the impact of transmission of resistant microorganisms and/or the genes encoding for resistance have not been fully investigated in feedlot cattle. In the current thesis, an agent-based model (ABM) was developed under the context of emergence and transmission of AMR within and between feedlot cattle. The objectives of the first experiment were to investigate the influence of on-arrival injectable metaphylaxis options on AMR in feedlot cattle, and of the second experiment were to explore the transmission of resistance determinants through animal-to-animal contact and contact with fecal contamination of the environment. In the first study, resistance prevalence to florfenicol, trimethoprim sulfadoxine (TMS) and tetracycline was assessed in both M. haemolytica and E. coli. Three different on-arrival metaphylaxis options were considered, including oxytetracycline, tulathromycin or no drugs administered. Resistance prevalence was lower for antimicrobials specifically used to treat BRD following on-arrival metaphylaxis when compared to no injectable metaphylaxis, but only when the antimicrobial used for treatment differ from those used for metaphylaxis. The results suggest there could be less opportunity for resistance selection to antimicrobials used for treating BRD as a consequence of reduced therapeutic AMU due to metaphylaxis administered on arrival. While metaphylaxis will select for resistance to the agent used on arrival, it could potentially minimize selection for resistance to other more medically important drugs used for BRD therapy when compared with no metaphylaxis on arrival. In the second study, the ABM developed in this study successfully replicated previously observed resistance prevalence for M. haemolytica and E. coli in a typical western Canadian feedlot setting assuming selection due to AMU, transmission of AMR, and a combination of both. The potential importance of transmission of AMR either directly from animal to animal or through the environment must be considered when evaluating expected benefits to antimicrobial stewardship efforts. Further, insights generated from the current ABM can assist policy development and decision making in prevention of AMR.



feedlot cattle, antimicrobial resistance, agent-based modeling



Master of Science (M.Sc.)


Large Animal Clinical Sciences




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