Johne’s disease is caused by the bacteria Mycobacterium avium subspecies paratuberculosis (MAP) and is a costly, chronic, debilitating disease. Animals with Johne’s disease are likely to be culled earlier, and more likely to be affected by other conditions, including chronic mastitis and lameness. Johne’s positive cows have been shown to be twice as likely to have a

SCC >200,000 and yield 25% lower than the herd average. In herds with a high level of the disease the cost is estimated to be 1-2 ppl.

80% of infections occur in the first month of life, from infected faeces, colostrum or milk being ingested and it can take several years before signs of the disease appear. During this period, it is difficult to identify these animals. Animals often begin to shed MAP and spread the disease before showing signs of Johne’s. Around the time shedding begins, antibodies are produced and we can then identify these cows.

Testing can be performed on both blood and milk with similar results. In order to control Johne’s on a farm, cow’s likely to be a risk to calves must be identified through regular testing (ideally quarterly) so they can be managed separately at calving.