Milk quality assurance for paratuberculosis: simulation of within-herd infection dynamics and economics

Maarten Weber , Mirjam Nielen , Annet Velthuis , Herman van Roermund

A bulk milk quality assurance programme for Mycobacterium avium subsp. paratuberculosis (Map) in dairy herds was simulated with a stochastic simulation model (JohneSSim). The aim of this study was to evaluate the epidemiological and economic effects of preventive management measures and various test schemes in a simulated population of closed Dutch dairy herds over a 20-year period. Herds were certified as 'low-Map bulk milk' if, with a certain probability, the concentration of Map in bulk milk did not exceed a maximum acceptable concentration of 10$^{3}$ Map organisms per litre (based on pasteurisation studies). The programme started with an initial assessment; test-negative herds entered a surveillance procedure and test-positive herds a control procedure. The simulations showed that herd examinations by ELISA for the initial assessment, surveillance and control procedures effectively ensure the quality of 'low-Map bulk milk': $>$ 75% of simulated herds were certified and $>$ 96% of certified herds produced bulk milk with $<$ 10$^{3}$ Map/L if the initial herd-level prevalence was 30%. Preventive management measures only had a minor effect on bulk milk quality of certified herds. Culling based on biennial faecal culture was more effective than culling based on annual ELISA. Average total discounted costs for 20-year participation in a programme consisting of initial assessment by ELISA, surveillance by biennial ELISA and control by biennial faecal culture were $16{\rm Euro}\times10^{3}$ per herd. In conclusion, this study shows that a bulk milk quality assurance programme for closed Dutch dairy herds is feasible and provides information on the cost-effectiveness of different programmes. The concepts of this study equally apply to other countries because mechanisms of paratuberculosis infection, disease, and testing are comparable in other dairy cattle populations.

Mots clés: dairy cattle; milk; paratuberculosis; stochastic simulation model; quality assurance programme

Domaines: Biologie moléculaire; Génétique animale; Biologie cellulaire; Interactions cellulaires [q-bio.CB]; Microbiologie et Parasitologie; Immunologie; Neurosciences [q-bio.NC]; Santé publique et épidémiologie; Biologie animale

Maarten Weber, Mirjam Nielen, Annet Velthuis, Herman van Roermund. Milk quality assurance for paratuberculosis: simulation of within-herd infection dynamics and economics. Veterinary Research, 2008, 39 (2), pp.1-20. ⟨10.1051/vetres:2007050⟩. ⟨hal-00902895⟩