HBS, Produktions- og Sundhedsstyring i Besætninger
Long-term effects of paratuberculosis on within-herd prevalenceand on-farm economy of implementing risk-based control strategieswere compared with alternative strategies by using a herd-simulationmodel. Closing transmission routes is essential for effectivecontrol of paratuberculosis. However, many farmers lack theresources to carry out these procedures for all cows in theherd. When using risk-based control strategies 1) all cows aretested quarterly with a milk ELISA, 2) specific cows with ahigh risk of being infectious are identified, and 3) the farmercan focus only on these infectious animals to close infectionroutes. In this way the workload can be reduced, making thesecontrol strategies more feasible. This study evaluates potentiallong-term effects of the risk-based approach compared with non-risk-basedstrategies by simulations conducted with the herd-simulationmodel PTB-Simherd. Seven control strategies were simulated inherds with initial true herd prevalences of 5, 25, and 50%,respectively. The results predicted the risk-based control strategiesto be very efficient and comparable to the best whole-herd strategiesin reducing the within-herd prevalence of paratuberculosis withconsiderably less labor. If infection routes are closed efficiently,prevalence can be reduced to 10% of initial prevalence within5 to 7 yr. Test-and-cull strategies without closing infectionroutes were found, by simulation, to be ineffective in reducingprevalence and were not cost-effective methods. The profitabilityof the various control strategies depends on hourly wages andtime spent per cow/calving. Furthermore, simulations show thatimmediate culling of highly infectious cows is only necessaryand cost-effective if infection routes from these cows are notefficiently closed. The risk-based control strategies are recommendedin the Danish voluntary control program "Operation Paratuberculosis,"which was initiated in February 2006 and now includes 1,220dairy farmers in Denmark.