Disease and economic impact estimation of Mycobacterium avium ssp. paratuberculosis infection in Swiss dairy herds

Paratuberculosis (PTB), also known as Johne's disease, is a widespread endemic disease affecting various ruminants and other animals globally. The disease, caused by infection with Mycobacterium avium ssp. paratuberculosis (MAP), leads to considerable economic losses in the dairy industry worldwide. The aim of this study was to assess the economic impact of PTB in the Swiss dairy cattle population. A case-control study was first conducted to compare the production parameters milk yield, SCC, subclinical mastitis (SCM) prevalence, calving interval, service period, and 56-d nonreturn rate between MAP-positive (n = 31) and MAP-negative (n = 31) herds. The comparison was carried out using regression analysis based on data from breeding associations. Subsequently, gross margins, production losses, and expenses caused by PTB were estimated based on empirical and literature data using stochastic simulation models. The regression analyses showed minor differences between MAP-positive and MAP-negative herds, and none of these were significant. Case herds produced 0.07 kg/d per cow less milk than MAP-negative herds and had on average higher SCC. No significant differences were found in SCM prevalence or in fertility parameters. Despite the lack of statistically significant differences in health and production parameters between positive and control herds, potential economic costs of PTB were assessed. The statistical power of the study was limited, but even small decreases in production can eventually lead to substantial financial losses. The annual financial losses per cow in a MAP-positive herd were estimated to be approximately 36 Swiss francs (CHF). On national level, the annual losses due to MAP infection were estimated at CHF 682,767 for the Swiss dairy producers. The model outcomes demonstrate that even minor effects of PTB lead to substantial economic losses for Swiss dairy producers. This study provides important insights for the evaluation of potential management measures, such as regional or national control programs.