title: Milk quality assurance for paratuberculosis: simulation of within-herd infection dynamics and economics.
abstract: 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 Euro x 10(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.
authors.affiliation: Animal Health Service, PO Box 9, 7400 AA Deventer, The Netherlands. m.weber@gddeventer.com
authors.forename: Maarten F
authors.initials: MF
authors.lastname: Weber
authors.forename: Mirjam
authors.initials: M
authors.lastname: Nielen
authors.forename: Annet G J
authors.initials: AG
authors.lastname: Velthuis
authors.forename: Herman J W
authors.initials: HJ
authors.lastname: van Roermund
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000191:economics* / Q000453:epidemiology* / Q000517:prevention & control; D003198:Computer Simulation; D003612:Dairying / Q000379:methods / Q000592:standards; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D008892:Milk / Q000191:economics / Q000382:microbiology / Q000592:standards*; D008954:Models, Biological; D016927:Mycobacterium avium subsp. paratuberculosis / Q000254:growth & development / Q000302:isolation & purification; D010283:Paratuberculosis / Q000191:economics* / Q000453:epidemiology* / Q000517:prevention & control; D015995:Prevalence; D011786:Quality Control; D013269:Stochastic Processes; D013997:Time Factors