Risk factors for antimicrobial use in pig farms: a cross-sectional study in the Netherlands

Abstract Background Antimicrobial use (AMU) has decreased by 63% in Dutch pig farms since 2009. However, this decrease has stagnated in recent years. The problem mainly pertains to weaners, which have a six-fold higher AMU compared to sows/suckling piglets and fatteners. The aim of this study was to identify farm-level characteristics associated with i) total AMU among weaners, sows/sucklings and fatteners and ii) use of specific antimicrobial classes in the former two age groups. Methods In 2020, data from 154 Dutch pig farms were collected and analyzed in a cross-sectional study. These data included information on AMU and farm characteristics, focusing on weaners. A mixed-effects conditional Random Forest analysis was applied to select the subset of farm characteristics that was best associated with AMU. Results Overall, the main risk factors for total AMU in weaners were vaccination for PRRS vaccination in sucklings, being a conventional ( vs organic or “The Better Life label”) farm, high within-farm pig density and early weaning. The largest protective effects for total AMU for sows/sucklings were E. coli vaccination of sows and having a search boar from own production. Regarding the other outcomes of those two age groups several risk factors overlapped such as farmer’s non-tertiary education, not having free-sow systems during lactation and conventional farming while another risk factor of interest for weaners were having fully slatted floors. In fatteners, the highest risk for their AMU was PRRS vaccination of sucklings. Conclusions Several on-farm characteristics associated with AMU in Dutch pig farms were identified. Some have been found elsewhere too, but others were novel, such as farmer’s education, lower pig aggression and free-sow systems, which were associated with decreased AMU. Certain farm practices can reduce structurally the need for AMU, as their effect is mediated through improvement of environmental conditions, biosecurity and animal welfare mitigating as such the risks of disease and stress in animals.