Associations between animal health indicators, antimicrobial use, and antimicrobial resistance on Swiss dairy farms

Farm animal health and welfare have been ongoing concerns for farmers, consumers, and society for a long time. Antimicrobial resistance (AMR) and its relationship with antimicrobial use (AMU) have been identified as global public health challenges. A set of established health and welfare indicators (HWI) for dairy cows and the increasing availability of detailed farm-level AMU data enabled us to carry out this study with the objectives to (i) investigate the relationship between HWI and farm-level AMU, (ii) capture the current situation of AMR in dairy cows and calves on the study farms, and (iii) identify associations between AMR presence, AMU, and management practices in Swiss dairy farms. High AMU farms (n = 22) and low AMU farms (n = 28) were recruited based on prescription records in the national AMU database. Current farm AMU was assessed quantitatively using an animal treatment index (ATI) based on antimicrobial prescription data. A combination of animal-based and data-based health indicators were assessed on all study farms and used to form a total health and welfare score (HWS). Associations between lower ATI and good health and welfare were found for the total HWS (estimate: -0.144, p = 0.03) and the partial score for HWI related to health (-0.111, p = 0.01). Several individual HWI (e.g. productive lifespan of cows, participation in animal welfare programs) were found to be significantly associated with either AMU group (high vs. low), ATI, or both. Pooled fecal samples were used to assess the presence of AMR in the study farms. Commensal Escherichia coli isolates from calves and cows were most commonly resistant to tetracyclines (36 % and 3 %, respectively), followed by penicillins (34 % and 1 %) and sulfonamides (32 % and 1 %). No significant associations were observed between AMU and the presence of AMR (overall and for specific antimicrobial classes) on the study farms. Several management practices reported by farm managers during interviews (e.g. feeding of waste milk with antimicrobial residues to calves) were significantly associated with AMU group and ATI, but none were associated with the presence of AMR. The results of this study may help to understand how AMU is related to HWI in dairy cows and support monitoring and benchmarking efforts to reduce AMU while maintaining high levels of cow health and welfare. Further research on a larger scale is needed to obtain more generalizable results and to further investigate the complex and multifactorial relationship between AMU and AMR.