The organism that causes Johne's does not grow in the environment, but it can survive in the environment a long time under the right conditions (cool and wet). The organism may survive six months to a year in a watering pond and a few months on pasture.
It is possible for Johne's infected bulls to shed the organism in semen, especially in advanced stages of the disease. However, artificial insemination is not considered an important risk for transmission. One reason this is true is because bull studs are regularly tested for Johne's disease.
Cows in advanced stages of disease have transmitted the infection to unborn calves.
