Johne’s disease is a bacterial disease of cattle and other ruminants for which there is currently no cure. Johne’s is caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP).

The bacterium affects the guts of cattle which causes diarrhoea and wasting.

Cattle can become infected at any age but usually are infected as calves by drinking or eating food contaminated by the bacteria.

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The bacterium is spread through dung or milk of an infected animal. Calves can, but rarely do, become infected while still in the womb.


Symptoms vary depending: on the stage of infection; on how many bacteria the calf swallowed; on how soon after birth this happened; and how quickly the gut wall has become damaged.

Once a calf becomes infected with Johne’s, this calf can then spread it to other calves and other cattle that it comes into contact with.

The signs of infection appear very gradually with reduced feed conversion efficiency leading to loss of productivity followed by weight loss, scour and ultimately emaciation and death.

Very commonly, signs of Johne’s disease won’t actually be visible until the animal has had three or more calves.

However, even before signs are seen, the cow’s resistance to other infections may have already been weakened and she may well have been culled for poor performance due to mastitis, lameness or poor fertility, without this even having been linked to Johne’s disease.


One-off tests to diagnose Johne’s only pick up some of the infected animals.

The best practice is to test regularly over time, with the help of a vet to read the results. This helps to build a profile of Johne’s in your herd.