How TB testing works

Skin testing

Depending on where your farm is, you’ll get a visit from one of our TB testers who perform skin tests on animals in dairy, beef and deer herds. Your farm’s disease status and location will determine whether that happens:

• every year
• every 2 or 3 years, or
• when stock moves between farms.

To TB test an animal, a small dose of purified proteins from TB bacteria (called tuberculin) is injected into the skin. If an animal has been exposed to TB, we'll see localised swelling at the injection site. This is a sign that TB could be present, which a blood test will help to confirm.

An animal that has a positive reaction to a skin test is called a 'reactor', and your TB tester will tag it with an official orange ‘reactor tag’. It’s illegal to tamper with — or remove — reactor tags without our approval. The tags must stay on until:

• the animal is slaughtered, or
• a blood test confirms the animal is unlikely to have TB.

Blood testing

When an animal tests positive to a skin test, they're usually given a blood test next. This is because skin test reactions can be caused by other organisms — like Avian TB, Johnes disease and woody tongue — so they can produce a ‘false-positive’ reaction. You might hear this test being referred to as the Interferon-Gamma test, or Bovigam.

The blood sample is taken between 10 and 30 days after the skin test results have come through. Blood samples are processed on Thursdays and Fridays each week, and we’ll call you on the Monday or Tuesday of the following week with the result.

You can’t move any stock off your property while you’re waiting for blood test results, to make sure there’s no risk of TB spreading further. However, if there are special circumstances in which you must move an animal, call our contact centre on 0800 482 463 to discuss your options.

Getting blood test results

If the blood test result is negative, you’ll get instructions on how to remove the orange reactor tag.

If the result is positive, the reactor animal will be slaughtered so we can complete a post-mortem on it, to confirm if TB is present or not. You’ll get a call from one of our disease management vets, and we’ll arrange for the animal to be valued and then moved to a meat processor for slaughter. While you’re waiting for the animal to be moved to slaughter, you must:

• ensure the animal does not leave the property
• leave the orange reactor tag on the animal.

Animals tagged with orange reactor tags, including those going to slaughter, can't be moved off the farm until we issue a ‘Permit to Move’.

If the infected animal is a dairy cow, you also need to separate it from the rest of the herd, and remove its milk from supply.