Changes in antimicrobial resistance profiles of Escherichia coli and the metagenome on Dutch pig farms after antimicrobial usage interventions.

The use of antimicrobials in livestock farming drives selection and dissemination of antimicrobial resistance (AMR), prompting implementation of veterinary stewardship programs to reduce antimicrobial usage (AMU). We evaluated changes in AMR on 45 Dutch pig farms before and after tailored, coaching-based interventions using phenotypic testing of Escherichia coli and metagenomic profiling of pooled faeces. Post-weaning pig farms, including nursery and fattening units, entered the intervention in a stepped-wedge design, with intervention periods ranging from 10 to 27 months. Across farms, AMU and abundances of several antimicrobial resistance gene classes declined over time, alongside reductions in overall resistome levels. Proportions of phenotypic AMR in E. coli were more variable, although decreased AMU was associated with lower resistance for specific antimicrobial classes, such as tetracyclines and beta-lactams. While longer follow-up is required to fully assess long-term impacts, these findings indicate that veterinary antimicrobial stewardship programs can yield measurable short-term reductions in AMR at farm level.