Prevalence of Johne's on US dairy farms is estimated at one-fifth of all herds, and is higher for the population of large herds. Of the animals which test positive for MAP, high levels of bacterial shedding are noted in only a small proportion. Despite this low prevalence of high-shedding animals, elimination of MAP from herds has proven exceptionally challenging, with few published reports of successful eradication of MAP from infected farms. Mathematical modelling may aid us in the understanding of this apparent contradiction.In this study we developed a deterministic mathematical model of MAP transmission on commercial US dairies which builds upon and modifies the assumptions in previous work to best reflect the pathobiology of the disease. Transmission was modelled using ordinary differential equations. Calculation of transmission parameters in these models is necessarily non-linear. Previous models of disease have only utilized linear dynamics and therefore lack sensitivity to changes in susceptible population size. Values gathered from literature concerning animal turnover in US dairy herds were utilized, and rates of transition from disease states were calculated from retrospective fecal culture data from herds in New York and Pennsylvania. The model conforms with the expectation that aggressive test-and-cull strategies do not result in successful elimination of MAP in a short timeframe. Model output illustrates relative insensitivity of infectious transmission to the presence of high shedding animals. Multiple levels of contagiousness among infected adult animals and introduction of the contribution of MAP bacteria from infected calves was able to explain the maintenance of low prevalence infections in herds. Although previous experimental studies support the potential of infectious transmission among young calves, further research is needed to verify existence of a pool of infectious young animals. If this group of animals is diagnostically identifiable, elimination strategies may need to address this route of transmission.