Multiple studies indicate that host animal genetics play a role in susceptibility to Mycobacterium avium subsp. paratuberculosis (MAP) infection. However, due to differences in methods used to define MAP-infected animals and controls and differences in methods of genetic analysis, there is as yet no clear consensus on the genes or markers to reliably define the MAP infection susceptibility of any animal species. Meta-analysis of combined studies and larger studies will help resolve the situation in the coming years.