Agriculture Minister Andrew Muir has insisted it is “very rare” that a non-infected animal will be wrongly classified as having bovine TB.

In an answer to a written question from Newry and Armagh DUP MLA Gareth Wilson, Minister Muir said the current skin test has a very high specificity of 99.98% which means the chances of a TB-free animal being wrongly classified is approximately one in 5,000.

While the test might have a high specificity, in practice only around half of TB reactors have visible lesions at slaughter and/or culture positive in laboratory testing.

In 2025, out of 18,892 skin test reactor cattle, just 10,093 had visible lesions and/or a positive lab test.

However, Minister Muir explained that the 8,799 cattle without lesions etc. are not false positives.

Instead, he said visible lesions are not considered a standard for disease confirmation, but rather an indication of disease progression. “Visible TB lesions may take months or years to develop, and given the specificity of the test, most reactor animals with no visible lesions will actually be infected,” he said.

He also pointed out that not all reactor animals have samples submitted to the laboratory.

The main issue with the current skin test is that it has a sensitivity of around 80%, so it will leave behind some reactor animals.

In contrast, the interferon gamma (blood) test has higher sensitivity, but lower specificity than the skin test, so around 3 to 4 cattle in every 100 will be wrongly assessed as having TB.

In 2025, there were 1,379 cattle with a positive blood test for TB, with 393 of these having visible lesions at slaughter.

“The blood test will identify animals at an earlier stage of infection than the skin test,” said Minister Muir.