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TB test

In order to move or trade cattle, herds need to be free from infection and classified as Officially Tuberculosis Free (OTF).

Cattle testing in Wales

Cattle keepers are required by law to have their cattle tested for bovine TB. In Wales all cattle herds are tested at least once a year, with the exception of calves under 42 days at the time of the test. Cattle are tested to make sure that they are free from bovine TB and to allow Officially Tuberculosis Free (OTF) herds to trade cattle. Cattle are also tested to identify those herds which are infected.

TB Tests

There are two different official cattle tests which are approved for use within European Union (EU) Member States:

  • the ‘skin test’
  • the ‘gamma test’.

These tests detect an immune response to bovine TB and can identify infection before cattle show any signs of illness. Removing infected cattle as early as possible reduces the chance of them infecting others.

No diagnostic test is perfect and neither test is 100% accurate in every circumstance. It is for this reason that infected herds have to have at least two clear tests before movement restrictions are lifted. This reduces the risk of infected animals remaining undetected within a herd. 

Tuberculin skin test

The skin test is used as the main screening test. The test is good at finding infected herds and is very good at correctly identifying uninfected cattle. After identifying infection in a herd a stricter interpretation of the next test result is used. This increases the test’s ability to identify any remaining infected cattle.

The skin test has been effective in clearing infection from parts of the UK where TB infection in wildlife is not a significant problem. Scotland achieved TB free status through testing and removing infected cattle.

Gamma interferon blood test

The gamma test is used to complement the skin test and can detect infection earlier. When used alongside the skin test it improves the likelihood that infected cattle will be identified.

The gamma test is a more expensive test to use and it requires a blood sample. It is not as good as the skin test at correctly identifying uninfected cattle. This means that, if it was used instead of the skin test, there is a small risk that some herds would be incorrectly identified as being infected. Because of this we do not use the gamma test as the main screening test. We use it in infected herds in specific circumstances:

  • in less infected areas of Wales, to help stop TB from becoming established
  • in areas where TB is more common, to help clear infection from herds more quickly.

Post mortem and culture

Post-mortem inspections are performed on all cattle carcases to check if meat is safe to eat. Microbiological culture is a laboratory test used to demonstrate the presence of Mycobacterium bovis (bovine TB). It can also identify the exact type of bovine TB. Post-mortem and culture can fail to identify if infection is present. It is for this reason that the skin and/or gamma test results are used to determine if a herd or animal is infected.

DNA tagging

Cattle testing positive for bovine TB are DNA tagged to further strengthen controls preventing spread of the disease. This helps to clearly identify reactor cattle for removal. Samples are cross-checked against the DNA of cattle sent to slaughter to verify that the correct cattle have been slaughtered.