Assessment of Antimicrobial Use and Resistance Patterns in Dairy Cattle Operations in Green Valley Farms

Thesis Abstract

Antimicrobial resistance (AMR) in dairy cattle presents a significant threat to livestock productivity, public health, and antimicrobial efficacy, particularly within intensive farming systems where antimicrobial usage (AMU) is prevalent. Despite global concerns, there is limited region-specific data on the patterns of antimicrobial administration and the corresponding resistance profiles in dairy farm settings, especially within Green Valley Farms, a large-scale dairy operation employing over 3,000 cattle. This study aims to assess the current practices of antimicrobial use and characterize the antimicrobial resistance patterns among bacterial isolates in dairy cattle operations at Green Valley Farms, thereby informing policy and antimicrobial stewardship strategies. The primary objectives are to quantify antimicrobial use (AMU) in different phases of dairy production, identify the commonly used antimicrobial agents, determine the prevalence of resistant bacterial strains, and analyze associations between AMU practices and resistance patterns. A cross-sectional, mixed-methods research design was employed, integrating quantitative surveys, laboratory microbiological analyses, and qualitative interviews. The population comprised farm managers, veterinarians, and dairy cattle, with a stratified random sampling approach selecting 150 dairy cattle across various production groups and 20 key informants. Data collection involved structured questionnaires to document antimicrobial administration practices, farm records review, and aseptic sampling of bovine nasal, rectal, and milk specimens for microbiological testing. Antimicrobial susceptibility testing was conducted on bacterial isolates utilizing the disk diffusion method, following Clinical and Laboratory Standards Institute (CLSI) guidelines. Data analyses encompassed descriptive statistics to depict AMU patterns, Chi-square tests for prevalence comparisons, and multiple logistic regression models to explore associations between antimicrobial practices and resistance patterns. Thematic analysis was applied to qualitative interview transcripts to contextualize quantitative findings. It is anticipated that the findings will reveal high frequencies of broad-spectrum antimicrobial usage, particularly tetracyclines and aminoglycosides, correlating with elevated levels of resistant strains such as Escherichia coli, Salmonella spp., and Staphylococcus aureus. Regional resistance patterns are expected to indicate multidrug-resistant organisms, especially in strains isolated from animals with histories of frequent antimicrobial treatments. These results are expected to demonstrate statistically significant associations between indiscriminate antimicrobials use and the emergence of resistant phenotypes, supporting the hypothesis that current AMU practices contribute substantially to AMR development in dairy cattle at Green Valley Farms. This research will contribute novel, context-specific data to the understanding of antimicrobial consumption behaviors and resistance dynamics within a large-scale dairy setting, addressing a critical gap in regional epidemiological knowledge. It will advance the theoretical understanding of the relationship between antimicrobial stewardship practices and resistance emergence, consistent with the One Health framework that recognizes interconnected health outcomes across humans, animals, and environment. Additional insights will emerge regarding the influence of farm management practices, veterinary oversight, and farmer perceptions on antimicrobial stewardship. In conclusion, the study will underscore the urgent need for targeted interventions to optimize antimicrobial use, enhance prudent prescribing policies, and implement effective resistance mitigation strategies within the dairy industry. Recommendations will include developing farm-specific antimicrobial stewardship programs, strengthening regulatory oversight, and promoting farmer education on responsible antimicrobial practices. Further research avenues will be proposed to explore longitudinal resistance trends and evaluate intervention efficacy over time. This work aims to inform policymakers, veterinarians, and dairy farmers, fostering sustainable antimicrobial stewardship and safeguarding both animal health and public safety.