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Johne's Disease in Dairy Herds

Johne‘s disease is an infectious wasting condition of cattle and other ruminants caused by Mycobacterium avium subspecies paratuberculosis (commonly known as Map). It is closely related to the organism that causes tuberculosis. The disease progressively damages the intestines of affected animals, and in cattle this results in profuse and persistent diarrhoea, severe weight loss, loss of condition and infertility. Affected animals eventually and inevitably die. In dairy herds, the presence of Johne’s disease will significantly reduce milk yields well before other signs of the disease can be found. Although not a notifiable disease in Great Britain, Johne’s disease is notifiable in Northern Ireland.

You can download information on Johne’s Disease from this website or call the Defra Publications line on 0845 955 6000 quoting publication number PB9990.


Why should farmers care about Johne’s disease?

The disease can have a significant financial impact on herds through loss of output and early culling. It has been suggested that this organism may also be a possible cause of Crohn’s Disease in humans. Such a causal link between the two conditions has yet to be proved or disproved, however the Government is taking a precautionary approach in this area. A possible route to infection in humans could be through consumption of milk containing Map.

Control and prevention of Johne’s disease makes sound long term sense for three reasons:
1. To reduce or prevent your production losses and income that result from this disease;
2. to increase the value of your breeding stock if your herd is certified as free of the disease and
3. to reduce the level of Map in milk and the environment.

The Food Standards Agency has published a strategy for reducing the levels of Map in milk. The strategy includes the following components:

How is Map spread?

Diseased animals in general pass large numbers of Map in their faeces (dung). A single diseased animal can therefore pose a high risk to susceptible animals and in particular to the young calves in the herd. Diseased animals may also excrete Map in milk and colostrum. While cattle remain susceptible to infection throughout life, they are at their most vulnerable in the first few months of life. Calves may be infected in the womb but are more commonly infected through:

  • drinking contaminated colostrum;
  • ingesting dung that may be present on unclean teats;
  • contaminated feed; and
  • contaminated environment or water supplies.

How can you spot Johne’s disease?

Map is a slow growing organism. After infection, it may be years before the infected animal becomes ill. At the early stages of infection, the only way to confirm whether an animal has Johne’s disease is to carry out blood tests. These do not detect all infected animals, but at this stage are more likely to identify infection than tests for the organism itself. Signs of the disease are rarely seen before two to three years of age. Generally, there is a period of reduced milk output or fertility well before the animals begin to show signs of advanced disease. These signs include persistent and profuse diarrhoea and significant weight loss, and are seen most commonly in animals at three to five years of age. Once signs of disease have developed, examination of a dung sample through a microscope is a useful way to confirm the diagnosis.


Page last modified: May 3, 2007

Department for Environment, Food and Rural Affairs