Johne’s disease is a bacterial disease of cattle and other ruminants for which there is no cure. It is caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP), hence the other name for the disease Paratuberculosis. Cattle usually become infected as calves early in life by drinking or eating milk or food contaminated with the bacteria, which are shed in the dung or milk of infected adult cattle. On occasion, calves are already infected at birth, with this being most common when their dam has advanced disease. Sometimes one infected calf can infect pen-mates early in life. Once infected, the disease progresses slowly and silently. The signs of disease will vary depending upon the stage of infection, how many bacteria the calf swallowed, how soon after birth this happened and how quickly the gut wall has become damaged. The signs of infection appear very gradually with reduced feed conversion efficiency leading to loss of productivity followed by weight loss, scour and ultimately emaciation and death.