The present invention relates to materials and methods for identifying animals that are resistant or susceptible to diseases associated with intracellular parasites such as brucellosis, tuberculosis, paratuberculosis and salmonellosis. More particularly, the present invention relates to the identification of a gene, called NRAMP1, which is associated with the susceptibility or resistance of an animal, such as an artiodactyla to diseases such as brucellosis, tuberculosis, paratuberculosis and salmonellosis. Still more particularly, the present invention relates to the identification of specific sequences of bovine NRAMP1 which associate with resistance or susceptibility to ruminant brucellosis, tuberculosis, paratuberculosis and salmonellosis, and to the method of identifying said sequences to identify animals who are susceptible or resistant to disease.