Johne’s disease is an incurable infection in cattle that can devastate a dairy herd’s production.
It is caused by paratuberculosis, a subspecies of Mycobacterium avium, which is related to infectious organism that causes tuberculosis (TB).
The disease causes chronic diarrhoea, weight loss, and infertility. As there is little chance of recovery from an infection, it often proves fatal.
The infection is common with dairy herds, and significantly reduces an animal’s milk yield before displaying any other symptoms, making it difficult for farmers to spot or diagnose.
If a farm has poor management control, the contagious disease will spread silently, making it extremely difficult to detect and terminate the disease.
Good biosecurity measures must be in place to prevent the disease from entering the herd, or to prevent it from spreading after infection.
Johne’s disease can also leave the heard susceptible to other illnesses such as pneumonia and mastitis.
Possible risks
Some animals can release large amounts of the contagious paratuberculosis bacteria in their faeces despite appearing healthy and showing negative results for the disease in their bloods.
If importing slurry or manure, there is a risk of the slurry containing the bacteria, which will inevitably infect your paddocks when spread.
If calves are being contract reared, or if you have animals on an outfarm, these areas are also at risk of contamination, which will then spread when the animals return to the home block.
The same principal goes for animals who are attending shows or marts, or animals bought externally.
Bacteria can also enter the farm from dung on vehicles and equipment of visitors or contractors.
Reducing the risk
Effective biosecurity is the best way to keep Johne’s off the farm, as it can take years for the first symptoms to show after first infection, leaving time for the disease to spread within the herd.
Despite not being 100% accurate, blood tests are the best method of picking up early stages of Johne’s disease, therefore farmers should be ideally testing annually.
‘Closed herds’ have the best chance of not bringing the disease in, so farmers should reduce the number of bought-in animals, or source animals from low-risk herds that have shown negative blood test results for several years.
Slurry and manure imports should be minimised or avoided, if importing slurry, avoid grazing pastures that have been recently spread with the substance.
If you have animals grazing off farm – for example, contract reared calves – ensure the contractor has good biosecurity measures in place, and has low risk animals on farm.
Make sure visitors and contractors have clean equipment and boots when on the farm, and provide disinfectant baths for visitors.
The disease can also spread through water. Your herd should be drinking from the mains if possible.
However, many farms use private sources, such as wells. When supplying animals with this water, it should be tested regularly for paratuberculosis.
Farms should also fence off stagnant water sources, such as ponds, as these are perfect grounds for this organism to live in.
