Johne's disease is caused by the bacterium Mycobacterium avium subspecies paratuberculosis. Infection is targeted to the intestine wall, causing damage which results in a slow wasting disease characterised by loss of condition, scouring and death (or culling). Young animals are most susceptible to infection, but the disease has a long incubation period and is not usually noticed until the animals pass 18 months of age.
The Effect in Your Herd
In infected herds a high rate of wastage and increased culling rates are often seen in cattle between 2-4 years of age. Average annual losses are estimated at £2,600 in a 100 cow dairy herd, and £1,600 in a similar sized beef herd. (figures from NADIS bulletin 2007)
The Route of Transmission
The bacterium is shed in large quantities in the faeces of infected animals, and the calves of affected animals are more likely to be infected. The slow development of the disease means that spread of infection occurs before an animal can be detected as positive, and makes it hard to eradicate. Vaccination may prevent some clinical disease, but does not prevent new infections in the herd. Pasture becomes contaminated and ideally should be left for a year before cattle are allowed to graze.
|Disease and status||Animals to be tested||Action Required|
|1. Herd Test||All animals of 2 years old and over are tested.||
If clear : Risk Level 2 awarded. 3 clear annual tests allow Risk Level 1 to be awarded.
If positives detected:
≤3% positives in the test: the herd is classified as 'Risk Level 3'
>3% positives: the herd is classified as 'Risk Level 4'.
|2. Disease reduction||All animals of 2 years old and over are tested annually, quarterly testing may be useful in dairy herds.||Positive animals removed and management practices addressed to limit new infections.|
|3. Maintenance of Accreditation/ Risk Level 1||
The herd test as in step 1 is repeated annually
'Biennial testing' may be an option for those herds that have achieved Risk Level 1 status for at least 3 years and have at least 20 animals of 2 years old and over.
If herd test is clear, the herd remains at Risk Level 1.
For further advice on Biennial Testing, please contact the office.