Genetic factors are hypothesised to influence susceptibility to paratuberculosis, but as yet, no specific genes have been identified that correlate with either disease incidence or pathological changes. Nramp 1 is a highly conserved gene thought to encode a protein which performs an as yet unknown function in the membrane of phagosomes in macrophages. A single base mutation in Nramp 1 has been found in certain strains of mice. Animals with the mutated allele show increased susceptibility to intracellular pathogens such as Salmonella typhimurium, Leishmania donovani and BCG. Our work focuses on the effect of Nramp 1 on paratuberculosis, as we screen Johne's affected and non affected animals for the presence of this mutation, and determine its effect on the incidence and progression of paratuberculosis.