Antimicrobial Usage Among Different Age Categories and Herd Sizes in Swiss Farrow-to-Finish Farms

In the Swiss pig sector, the usage of antimicrobials has been recorded, evaluated and systematically reduced on a voluntary basis since 2015. This monitoring has been carried out using various methods thereby enabling continuous national scrutiny as well as international comparisons. To gain a better understanding of the dynamics of the antimicrobial usage on Swiss farms, consumption data of farrow-to-finish farms was analyzed for the within-herd relationships between different age categories and the influence of the herd size. The data was collected on 71 farms for the year 2017, encompassing the amount of active ingredients and number of defined daily doses Switzerland (nDDDch) in total and stratified for the different age categories of piglets, weaners, fattening pigs, and sows. The differences of nDDDch per animal between the age categories were determined by a Wilcoxon test and subsequent posthoc analysis according to Bonferroni. The within-herd relationships between the individual age categories as well as the influence of the herd size were analyzed by generalized linear regression models. The evaluation of the treatment days showed that 50% of the number of DDDch were used in piglets, 44% for weaners, and 3% each for fattening pigs and sows. Compared to the other age categories, the examination of the number of nDDDch per animal showed a significantly higher number for sows whereas for fattening pigs the number was significantly lower (P<0.01). The farm-based analysis using linear regression showed a relationship between antimicrobial usage in sows and piglets (P<0.001; adj. R2=0.1855). Similarly, a significant relationship between larger herd size and increased antimicrobial usage was observed (P=0.0197; adj. R2=0.0630). The present study provides a detailed insight into the antimicrobial treatment dynamics of farrow-to-finish farms. In particular, the age category piglets and sows with their higher number of treatment days in total or per animal are of interest as a target for a potential reduction in antimicrobial usage. Likewise, larger farms with higher management requirements were found to be of particular importance for the reduction of antimicrobial usage. Monitoring programs should therefore evaluate different age categories separately to identify problems and suggest possible solutions for individual farms.