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Johne's Disease

Johne's disease is a chronic, progressive intestinal disease caused by infection with Mycobacterium avium subspecies paratuberculosis (Map).
Animals are usually infected when young, with calves being 80% more susceptible in their first month of life. The calf may be infected while in the womb, by drinking infected colostrum and milk, or by ingesting faeces. The organism may last for a year in slurry or on pastures. An infected cow can shed billions of organisms into the environment for years prior to showing any clinical signs of the disease. Only 1-5% of infected cows in a herd will show clinical signs of the disease. The rest of the infected animals will appear healthy, highlighting the need for testing. Infection is almost always introduced to a herd by purchasing infected replacement breeding stock including bulls.


Herd Level Testing

NML recommends a 30 cow screen to detect herd level infection in dairy herds (blood screens can be performed for beef herds).  This should be targeted at the animals most likely to show a positive result. Cows should be between 3 and 7 years old and should be selected according to their condition, whether they have problems with lameness, high SCC or mastitis or whether they are depressed, poor performing individuals. 

Bulk milk Johne's tests are not recommended due to the false confidence that can be placed on "low" results.  A relatively high percentage of animals could be shedding antibodies into the bulk milk tank before the test would return a "medium" result. NML will not offer bulk milk testing after 1st June 2019.

Cow Level Testing

NML offers a number of flexible testing options to fit with any farm.  Ad hoc testing can be performed on blood or milk samples for any customer.  For dairy farmers, NML offers the CHeCS approved Herdwise Scheme, which is available to all NMR-recorded herds.  It involves testing milk recording samples for Johne's antibodies on a quarterly basis.  





To order individual milk tests for Johne's simply ask your NMR milk sampler to fill out a blue form to be included in with your recording samples.  For non NMR herds, please call NML to request sampling pots on 01902 749 920 or email

To order a blood test just ask your vet to take a blood sample and submit it to the NML laboratories.