Agriland Media Group is delighted to collaborate with the Department of Agriculture, Food and the Marine (DAFM) to bring you the ‘TB Awareness Series’.
When a herd that has had a TB breakdown has passed two consecutive clear tests, it is derestricted. Some farmers may think this means that there is no TB in their herd.
However, there may still be TB in the herd at a level not yet detected by the TB test. This is known as residual infection.
Residual infection occurs because of TB-infected cattle remaining in a herd after derestriction.
It is part of the reason herds that have previously had TB are at a significantly higher risk of experiencing a repeat TB breakdown.
In fact, 30% of herds in Ireland that go clear will have a breakdown within three years. One crucial factor contributing to this, is residual infection in the herd.
Why does residual infection occur?
While the TB skin and blood tests are the most reliable test available, they are not perfect and do not catch all TB-infected cattle.
As such, residual TB infection can remain in a herd when some TB-infected cattle do not react to the TB tests.
So why don’t TB tests catch all TB-infected cattle?
- Early infection: Cattle that are recently infected may not react to the test yet;
- Desensitisation: If cattle are tested too often or too soon after a previous test, they may not react;
- Other illnesses causing immunosuppression: Other infections including viruses, liver fluke, or negative energy balance post-calving can suppress the immune response;
- Severe TB infection: Cattle with a generalised overwhelming TB infection can become anergic and fail to react to the test;
- Latent TB infection: Sometimes the immune system walls off the TB infection, reducing the immune response over time so the cattle don’t react to the tests;
- Poor testing technique can miss TB-infected cattle.
What can you do to reduce the risk of residual TB infection?
You can significantly reduce the risk of residual infection on your farm by taking the following practical steps:
- Cull inconclusive cattle, even if negative on a subsequent test – the cattle at highest risk of harbouring residual infection are those that have an inconclusive result in a previous TB test. Inconclusive cattle are 12 times more likely to be a reactor at a future test and can potentially be spreading infection in your herd;
- Cull older cattle present at a previous breakdown: These cattle are more likely to have been exposed to TB and may be desensitised to the test;
- Hygiene and cleanliness: Keep your farm clean: TB bugs can survive for months in urine, faeces, mucus, and saliva, which contaminate slurry and farmyard manure. Regular, effective cleansing and disinfection helps get rid of TB bugs which may have persisted in your farm environment.
Improving your biosecurity protects your farm from TB:
Following these simple steps will help to protect your farm;
- Clean and disinfect regularly: Watch our video on effective farm cleansing and disinfection.
- Check farm machinery: Ensure that contractors clean and disinfect slurry spreaders and manure spreaders before they enter your farm.
- Grazing management: Don’t graze cattle on land recently treated with slurry or manure for as long as possible.