Antimicrobial use in Danish pig herds with and without postweaning multisystemic wasting syndrome

A retrospective cohort study was performed on 130 pig herds in Denmark, to assess the effect of PMWS on the use of antimicrobial drug. The study comprised 65 herds diagnosed with PMWS during 2003-2004, and matched by the veterinary practitioner with 65 herds free from PMWS. Information on antimicrobial use 1 year before and 1 year after the diagnosis was achieved from the National Prescription Medicine Monitoring Database, VetStat, and summarized on quarter within age group and herd. The multiple linear regression analysis comprised antimicrobial use as the outcome variable with (1) quarter relative to diagnosis of PMWS in the positive herd (same date for the negative match), (2) diagnosis of PMWS (same date used for matched PMWS(-) herd), (3) season and (4) temporal trend as fixed effects. Relative to the unaffected herds, the antimicrobial use in the sow units in the PMWS(+) herds was elevated significantly by 35% in the last quarter and 43% in the fourth quarter before positive diagnosis in the herds (p<0.05). In weaner pigs, the antimicrobial use increased significantly two quarters before, and one quarter after the positive diagnosis, by 68%, 91% and 124% respectively. In weaner pigs, effects were seen of herd size and season. The study support that increased morbidity occur for an extended period prior to the diagnosis of PMWS, both in the sow units and the weaner pig units and further indicate that the syndrome cease after the diagnosis, with a decrease in need for antimicrobial treatment.