Paratuberculosis remains one of the most important diseases of cattle worldwide. In cattle, the disease is debilitating and is characterized by weight loss and chronic diarrhea in the later stages of infection. However, cattle in the subclinical stages of the disease often show decreased milk production and are at higher risk for development of other common production diseases. Infections with Mycobacterium avium ssp paratuberculosis are difficult to control because of long incubation periods, the absence of clinical signs until advanced stages of the disease, and the lack of completely reliable diagnostic methods in the preclinical stages of the disease.