Johne’s Disease is a chronic bacterial infection of the intestine of animals, including cows. The disease is caused by Mycobacterium avium paratuberculosis (MAP). The target for MAP is the gastrointestinal tract, primarily the distal ileum. Calves swallow the organism via contaminated milk, water, feed, or even amniotic fluid. Yes, calves can be infected by the cow before birth. The infection in the ileum persists for years without any signs of infection, the animal is infected but is not sick and is not responding to the infection in any visible way. The MAP organism somehow turns off the bacteria fighting mechanism in the animal. Eventually the cow loses the battle with MAP and the infection spreads throughout the animal. Clinical signs, diarrhea, weight loss, and low production, usually begin to appear at this point and the cow only now, after years of infection, reliably produces the signal of the infection detectable by lab tests for antibody in the milk or blood. Unfortunately, the cow has been shedding MAP and potentially exposing calves this whole time. As the cow show signs and blood tests become positive, the cow is shedding more MAP and contaminating the environment. As the disease progresses the shedding increases.
How common is Johnes? A study in 2007 found 68% of the dairy herds in the USA were culture-positive. Considering the above information and the sensitivity of cultures, this 68% yields an estimated true herd prevalence of over 90%. When I did some herd ELISA testing for Johne’s many years ago, I was not able to find a negative herdmin Central Texas. So, everyone has infected cows. The question becomes, do the cows stay in your herd long enough to show clinical signs. Maybe not, since Johne’s is an immunosuppressive disease, most cows will leave the herd due to the direct impact of other diseases such as mastitis, metritis, or pneumonia which are more common in Johne’s positive cows than in negative cows. So. if you embark on a Johne’s control program, monitor the prevalence of all disease in your herd to see the benefits.
Johne’s control is not difficult, it takes time and effort. Sanitation and manure management are critical. You must protect your young stock by preventing ingestion of milk, water, or feed that contains MAP. Remember MAP can be anywhere that there is manure. Start with a clean calving area. Wait for feet to be showing before moving the parturient cow to the calving area. As soon as the calf is born, move the cow from the calving area to minimize manure contamination of the area. Move the calf to a clean hutch. Feed the calf pasteurized colostrum that should be MAP free. Thereafter, feed the calf only pasteurized milk or milk replacer. Do not allow cows to mingle with the calves. Feed monensin from birth to all calves and to cows throughout the full production cycle. Monensin suppresses MAP. Once a good control program is in place that keeps cows and their manure away from calves, you can start on a testing program. A reasonable program is to PCR test all cows at dry off by collecting at least 3 grams of manure from each cow. Properly label, package and ship the samples to the lab that can pool the most samples. TVMDL will only do 3 samples in a pool. Wisconsin VDL will do 5 samples per pool. Accession fees and shipping may negate the difference in pool size, depending on how many pools turn up positive. Once a cow is positive, assume she is positive for life. If you cannot cull her, breed her to beef semen and sell her calf at birth. Avoid keeping calves born to positive cows and use colostrum from positive cows only if absolutely needed and be sure it is pasteurized. Since most of the cows in the hospital pen are often Johne’s positive, avoid feeding hospital milk. Fresh cow milk is higher in antibodies that are very good for the calf compared to hospital milk. Also consider pasture drainage, water sources, and cropping practices that can produce MAP contaminated feed. This column was sourced from, and for further information see https://johnes.org, www.crohnscolitisfoundation.org, and www.rolfbenirschke.com. Also remember that everything you do to control Johne’s will also help control salmonella.