Genetic variation of susceptibility to Mycobacterium avium subsp paratuberculosis infection in dairy cattle

Paratuberculosis is an infectious disease that is not easily amenable to cl assical control methods such as treatment and vaccination. Experimental ani mal models suggest that there could be genetic factors responsible for susc eptibility or resistance to infection with the causative agent, Mycobacteri um avium subsp. paratuberculosis. The aim of this study was to estimate gen etic variation in susceptibility to paratuberculosis in Dutch dairy cattle. Data collected during a vaccination trial, conducted from 1984 to 1994, wa s used. A total of 3020 cows, with complete pedigree records and infection status at slaughter, were available for analysis. A standard polygenic stat istical probit model was used to estimate heritabilities. The estimated her itability of susceptibility to M. avium. subsp. paratuberculosis infection was 0.06 for the overall population. In the subpopulation of vaccinated ani mals the estimated heritability was 0.09. Other calculations based on the m odel used in this study argue against a prominent role for vertical transmi ssion. Because the establishment of genetic variation is one of the first steps to wards the exploration of the possible use of selection for genetic improvem ent, the present study provides evidence for the presence of genetic variat ion in the susceptibility of cattle to paratuberculosis. Because the econom ic impact of the disease is substantial, the development and application of genetic tools, along with other control methods, could be instrumental in the eradication of paratuberculosis.