Johne’s disease (JD), also known as paratuberculosis, is a chronic infection caused by a bacterium called Mycobacterium avium paratuberculosis (MAP). The bacterium infects the gut of cattle and other ruminant animals, causing the intestinal wall to gradually thicken and become inflamed. This results in leakage from the gut wall and prevents uptake of vital nutrients by the animal.
Johne’s disease is widespread amongst NZ dairy herds. Most infected herds harbour low levels of JD with occasional clinical disease. In some herds, Johne’s disease can cause annual losses of 1% and more in the milking herd.
Whole Herd Johne’s Testing
LIC offers whole herd Johne’s testing on herd-test milk samples to identify high-risk cows with advanced JD. These cows shed high numbers of bacteria and are a major cause of the spread of the disease to other animal’s especially young stock and calves.
Our testing may detect super-shedders that are not showing signs of the disease at the time of testing, but they are likely to develop clinical JD in the near future. The test will identify 8 to 9 out of 10 cows with clinical Johne’s or that are excreting large amounts of bacteria (heavy and super shedders).
The Antibody ELISA test detects the immune response of the animal to the MAP infection. While it generally does not identify cows during early stages of subclinical infection (ie low-risk non-shedders or intermittent / low shedding), the test performs very well in advanced stages of JD and will identify most heavy shedders.
Best time to test
The screening test should be carried out later in the season to maximise the benefits and identify as many high-risk cows as possible to be culled before calving.
As a rule, Johnes testing should take place at the February to March herd test for North Island, April to May herd test in the South Island.
Talk to your vet about a risk assessment and management plan for Johne’s disease.
To sign up herds for Johne’s screening at herd-testing, vets should contact the Animal Health Analyst team well in advance.
For further information, see the Johne's Disease information on the DairyNZ website.