Longitudinal study of antimicrobial use patterns, vaccination and disease prevalence in British sheep flocks.

BACKGROUND: The aim of the study was to describe the longitudinal dynamics of antimicrobial use (AMU) on sheep farms and explore associations between AMU and management factors, vaccination strategies, reproductive performance and prevalence of lameness.

METHODS: Antimicrobial supply data were collected for 272 British sheep farms for 3-6 consecutive years between 2015 and 2021. These data were obtained from the farms' veterinary practices.

RESULTS: Annual median AMU ranged from 8.1 to 11.8 mg/kg population corrected unit. AMU was skewed in each year with a small proportion of very high users. AMU within farms varied substantially between years. High AMU farms in 1 year were not necessarily high in other years. No associations between AMU and either vaccine usage or lameness prevalence were found.

LIMITATIONS: The study design requires veterinarians and farmers to volunteer their data. This unavoidably introduces the potential for a participation bias.

CONCLUSIONS: AMU on sheep farms is generally low, with a small number of farms being responsible for high usage. Targeting antimicrobial stewardship effort towards the small minority of persistently high users may be more appropriate than a focus on generic, industry-wide attempts to reduce overall AMU.