14t DEVELOPMENT OF THEDUTCHJOHNE'SDISEASECONTROLPROGRAMME SUPPORTEDBYASIMULATIONMODEL H.GROENENDAAL* 1 , M. NIELEN 1 AND J.W.HESSELINK 2 SUMMARY The development of a simulation model, 'JohneSSim', was part of a research effort in preparation for a national Johne's disease control programme. Initially, the focus was mainly directed on different compulsory 'test and cull' strategies. However, the results from the 'JohneSSim' model showed that eradication with only 'test and cull' strategies would not be possible within 20 years. Better calf management seemed more effective in reducing the prevalence. Overall,control wasnotaneconomicallyattractiveoption. Simulationofa strategy withan 'ideal test' (80%overall-sensitivity) showedthattheusage ofthistestwould result ina significant faster decrease of the prevalence but that this strategy was economically not attractive because of the high number of test-positive, young animals that had to be culled. Therefore, anewpotential control programmecalled, Paratuberculosis Programme Netherlands (PPN),was defined which was based on the stepwise improvement of calf hygiene, with little dependency on 'test andculling' at all. Themodelindicated that if farmers would consistently carry out the necessary management adaptations, this control programme decreases the prevalence considerably, and is economically more attractive (average benefit-costs ratio, excluding extra labour = 1.58) than previous plans. Based on the results of the 'JohneSSim' model, the new national voluntary Johne's disease control programme, PPN, was started in September2000. Thedecisionmaking hasbeengreatlysupportedby the'JohneSSim'model. INTRODUCTION Paratuberculosis in cattle is an infectious chronic granulomatous enteritis caused by Mycobacterium avium subs, paratuberculosis (Juste, 1996). In The Netherlands, paratuberculosis hasbeenpresent for alongtime,especially inthe low-lyingpeat moorsinthe northern part of the country (Benedictus, 1984). Organised disease control started in The Netherlands in the eighteenth century with governmental attempts to eradicate cattle plague (Huygelen, 1997). Since 1919, theAnimalHealth Servicehasusedfaecal cultures from clinical Corresponding address: CenterofAnimalHealthandProductivity,UniversityofPennsylvania, Schoolof VeterinaryMedicine, NewBoltonCenter,328 W.StreetRoad,KennettSquare,PA 19348, USA.Email: huybertg@cahp2.nbc.upenn.edu 1 FarmManagement Group, WageningenUniversity,Hollandseweg 1, 6706KN,Wageningen, The Netherlands. 2 AnimalHealthService, POBox9,7400AA, Deventer,TheNetherlands