Diseases associated with antimicrobial use in pig farms and risk factors thereof : A cross-sectional study in the Netherlands

Background: Current antimicrobial use (AMU) in Dutch pig farms is driven by herd health status, as only therapeutic AMU is permitted. This study focused on weaners and sows with suckling piglets to examine the diseases associated with i) overall AMU (measured in Defined Daily Dosage Animal per year – DDDA/Y), ii) use/not use of specific antimicrobial classes, iii) total consumption of specific antimicrobial classes (in DDDA/Y), and iv) farm characteristics linked to the occurrence of diseases that require AMU. Methods: Cross-sectional data on AMU, disease aetiologies for group treatments, and farm characteristics were collected from 154 Dutch pig farms, representing the situation in 2019. Associations between disease occurrence as a predictor and AMU (overall and by antimicrobial class) as an outcome were analyzed using multivariable generalized linear regression models. Subsequently, mixed-effects conditional Random Forest analysis was used to identify farm characteristics associated with these diseases. Results: Group treatments for musculoskeletal/neurological diseases (MNDs) in suckling piglets, and individual treatments (of unknown aetiology) in sows and suckling piglets, were significantly associated with total AMU there. AMU in weaners was significantly associated with respiratory diseases, MNDs, and individual treatments. Tetracyclines and penicillins were primarily used for respiratory diseases and MNDs in weaners, respectively, and for MNDs in sows and suckling piglets. Having a clear separation between clean and dirty outdoor areas in the farm and using boars from own production for estrus detection were both protective against occurrence of respiratory conditions in weaners, whereas PRRS vaccination in suckling piglets was a risk factor. Streptococcus suis vaccination in sows and fully slatted floors were both risk factors for MNDs in weaners, whereas being an organic farm was protective. Use of disinfecting powders in sows increased MNDs risk in suckling piglets and sows, and a longer lactation period was protective against respiratory diseases and MNDs in weaners. Conclusions: Respiratory diseases and MNDs in weaners appeared as the primary aetiologies for antimicrobial group treatments on Dutch pig farms. Prioritizing farm practices that enhance biosecurity and animal welfare is crucial for controlling these diseases and, consequently, reducing AMU.