Johne’s Disease: Cattle
The main way the disease spreads is when animals eat or drink feed and water contaminated with MAP. Infected calves, cows, and bulls shed the bacteria in their manure, contaminating the environment, including feed and water. Feed troughs, hay bunks, water tanks, ponds, stagnant water, maternity pens, and group pens can become contaminated directly from an infected animal or indirectly from equipment or people tracking manure on tires, boots, clothing, etc.
Newborns and young animals can ingest the bacteria from manure as they are being born, in the maternity pen, or on the dam. Colostrum or milk from infected cows is also a source of infection. Infected dams, especially if they are showing symptoms, can pass the disease on to their unborn calves.
Newborn calves or young animals are the most susceptible to infection. While animals develop some resistance with age, individual animals of any age can be infected if there are enough bacteria in the environment, feed, or water. All breeds of cattle, both dairy and beef, can be infected.
The number of animals showing symptoms does not reflect the total number of infected animals. For every animal showing symptoms, there may be 10 to 25 others infected. This is why you may see one case of clinical disease every few years, and then suddenly find 10 percent or more of your herd showing advanced signs.