Experimental animal infection models are crucial tools in the continuing fight to control and eradicate Johne's disease. The animal model selected and how it is utilised will depend on the outcomes required, such as immunological testing, pathogenesis and vaccine trials. The factors that appear to influence the outcome of experimental infections with Mycobacterium avium subsp. paratuberculosis (Mptb) are the species, breed and age of subject used for the infection, the route of infection, and the strain, dose and number of doses of Mptb used to inoculate the subjects. Studies to date have been lacking in the use of a defined type strain of Mptb in pure culture prepared from an archived seed stock that can be used at the same passage level in later trials. An ovine experimental oral infection model has been developed for Australian conditions using a pure culture of Mptb(Telford) retained as a freeze dried seed stock. This has been directly compared to oral infection with infectious gut tissue homogenate. While both experimental infections created disease closely resembling natural infection, not surprisingly the gut tissue homogenate challenged animals developed clinical disease earlier than animals given Telford strain Mptb. The results with the pure culture were repeatable over 3 trials.