Johne’s Disease (also known as “Johns Disease, JD, MAP, bottle jaw) is a cause of production and animal loss in the dairy industry, it also leads to poor reproduction. The bacteria is infectious to young animals and is a lifelong disease, although infected animals may take many years to show clinical signs. In addition, JD is a concern for our dairy product markets as there is an association of the causative bacteria of Johne’s; mycobacterium paratuberculosis (MAP), with Crohn’s disease in humans. Both diseases cause changes in the intestines which mean the patient cannot absorb their food properly. Presence of MAP in milk products is measured and is a potential trade barrier.
How do my animals get it?
Johnes is usually contracted from the contact of young animals with infected dams who are shedding the bacteria in their milk and faeces. Until they are about 6 months old, calves are unable to mount an immune response to the bacteria when they ingest it, therefore become infected. These animals have a subclinical infection, the bacteria sits hidden in their body but they may secrete the organism in their faeces and milk to infect other animals. The diagram shows the methods of infection in a dairy herd.
Subclinically infected animals also have a lower milk production and a lower in-calf rate than their uninfected herd mates. Eventually, they will develop clinical disease when their digestive system fails due to the granulomatous reaction to MAP in their intestines. The clinical JD cows are usually bright in the eye but lose condition and have a distinctive watery scour.
MAP is a resilient bacterium and persists in the environment for many months. Control programmes need young calves to be kept away from the faeces of adult cows. We have various tests for JD using faeces, milk and blood that can be used for identifying clinically and subclinically infected animals. The tests are not perfect, but they are an aid to identification of these animals.
If you would like to learn more about what you can do to control JD in your herd, talk to your veterinarian and attend one of the workshops being run during February by LIC and Anexa in the Waikato.