Endemic stability of disease within populations despite intervention strategies is a common problem. There are many mechanisms by which pathogens are able to sustain themselves at a low level in a large population. One mechanism illustrated relatively recently is that of backward bifurcation, where the effective reproduction rate is greater than or equal to the basic reproduction rate. We demonstrate one possible instance of backward bifurcation in the real world, using Mycobacterium avium subspecies paratuberculosis (MAP) in dairy cattle as our model system. We use a mathematical model to illustrate transmission dynamics on dairy farms. Following the results of recent analysis of age-and-dose dependent shedding of MAP, we are able to build a model incorporating true values of exit from each infectious category. We show the influence of calf-to-calf transmission. The presence of age- and dose-dependent shedding of MAP among calves creates a bistable prevalence of infection following intervention.