Antimicrobial usage in farm animal practices in the UK: A mixed-methods approach

Antimicrobial resistance (AMR) is a growing One Health problem. Monitoring antimicrobial usage in farm animals is crucial for tackling AMR. A cohort study using the electronic clinical records during 2019 from 23 farm animal veterinary practices across the UK belonging to two corporate groups, with a range of 2-14 veterinarians per practice, estimated the usage of antimicrobials and highest priority critically important antimicrobials (HP-CIAs). Risk factors for using HP-CIAs were evaluated using hierarchical mixed-effects logistic regression modelling with practice ID and farm ID added as random effects. Using a qualitative approach, veterinarians from one of the participating practice groups were recruited for a qualitative study to explore the barriers and facilitators in relation to antimicrobial use. Semi-structured interviews were conducted with participants and analysed thematically. During the year 2019, 98,824 antimicrobial prescribing events overall were recorded from the treatment records of the 23 participating practices. The median count of antimicrobial events per practice was 3226 (range 263-22,159). There were 17,111/98,824 (17.3%) HP-CIAs events overall, with a median of 15.4% at practice level (range 4.8-22.1%). Penicillins were the most frequently used antimicrobials 29,539/98,824 (29.9%) followed by tetracyclines 19,015/98,824 (19.2%). HP-CIA use was strongly clustered, with more clustering seen at the farm level (intraclass correlation coefficient (ICC)= 0.56) than at the practice level (ICC= 0.32). Country, route of administration, season and practice type were significantly associated with the usage of HP-CIAs. Four main themes were identified from the analysis of the veterinarians' interviews: pressure from the industry, drug-related factors, knowledge level of veterinarians and clinical factors. Supermarket contracts and farm assurance schemes were facilitators for reducing antimicrobial use and the use of HP-CIAs. Ease of administration and the withdrawal period of the antimicrobials influenced veterinarians' choice of antimicrobials. The clinical condition and clinical signs presented on farm were reported to influence participating veterinarians' prescribing decision. Participants showed a good understanding of AMR, responsible use of antimicrobials and the term 'critically important antimicrobials'. In conclusion, integrating the quantitative and qualitative findings can inform policymaking on antimicrobials stewardship in farm practice. By estimating the relative levels of clustering of antimicrobial use at the practice and farm level, as well as identifying major risk factors for using HP-CIAs, more targeted interventions can be designed to promote responsible antimicrobial use in farm practice. Furthermore, better understanding the industry pressures on farms to reduce antimicrobials usage could reduce the barriers for responsible antimicrobial use by veterinarians.