This TB cattle control enhancement was introduced by Defra in November 2017 following a public consultation.
The main test used in Great Britain for detecting TB in cattle is the single intradermal comparative cervical tuberculin test (SICCT), more commonly known as the tuberculin skin test. The skin test in cattle relies on detecting and measuring the immune response of the animal to tuberculin, a protein produced by Mycobacterium bovis, the bacterium that causes TB in cattle. The skin test is comparative as the animal’s immune reaction to injections of both bovine and avian (bird) tuberculin is measured and compared. Cattle infected with M. bovis tend to show a greater response to bovine tuberculin than avian tuberculin. Depending on the degree of reaction to the skin test, the animal is classified as negative positive or inconclusive.
IRs are placed under movement restrictions and must be isolated until they are re-tested. The soonest an IR can be re-tested is 60 days after the injection date of the previous test. If the IR tests clear at the re-test, it is known as a ‘resolved IR’. If the IR fails the re-test (i.e. it has a positive result or an inconclusive result for a second time), the animal is compulsorily slaughtered and movement restrictions are placed on the whole herd if that has not already happened. In severe TB breakdowns, IRs may be compulsorily slaughtered at the discretion of APHA as direct contacts (DCs), without a re-test, and with compensation paid.
The TB risk posed by resolved IR animals
Scientific studies looking at resolved IRs in the Republic of Ireland1,2 where bovine TB is widespread, have demonstrated that such animals have significantly higher odds of becoming reactors at a subsequent test in the same or another herd. The studies concluded that:
- Resolved IRs that moved out of the herd after passing their re-test were 12 times more likely to be disclosed as a reactor at the next test compared to all other animals in the national herd.
- Between 11.8% and 21.4% of IRs slaughtered prior to re-test showed visible lesions suspicious of TB at post mortem meat inspection, compared with less than 0.5% of non-IR animals.
These studies provided evidence for the introduction of a new policy for resolved IRs in the Republic of Ireland in 2012. After reviewing the evidence, Defra introduced a similar policy in England.
Analyses of cattle herds in England in 2018 showed that over 40% of IR-only herds went on to have a TB incident within the following 15 months in the High Risk Area (HRA), with a substantial proportion similarly affected in the Edge Area (38%). This indicates that IRs are an important predictor of the presence of TB infection and supports the policy to restrict resolved IRs for life to the herd in which they were found3. Further research has been carried out exploring the risk posed by IRs in England and Wales, which adds to the evidence from similar studies conducted in the Republic of Ireland 4 . This latest research found that the odds of an animal becoming a subsequent reactor during the study period were greater for IR animals than for negative testing animals in the HRA and Edge Area of England, and in Wales.
Why not just compulsorily slaughter all IRs?
Compulsory slaughter of all IRs would increase the probability of rapidly removing all TB-infected animals in herds. However it would be at a disproportionate cost, as increased numbers of TB-free cattle would be slaughtered resulting in additional herds being unnecessarily placed under movement restrictions.
This is why the government adopted the alternative approach of restricting resolved IRs to the holding in which they were found for the rest of their life. This contains the potential disease risk to that holding and reduces the risk of spread of disease. Cattle keepers have the option to slaughter resolved IRs, effectively removing the risk from the herd.
Restriction of resolved IRs for life
All IRs in the HRA and Edge Area (and in TB breakdown herds in the LRA) that have a negative result on re-testing remain restricted for the rest of their life to the holding in which they were found. The only permitted off movements for such animals are to a slaughterhouse or Approved Finishing Unit (AFU). The cattle can move directly or via an approved slaughter gathering or TB dedicated sale (orange market). To release resolved IRs in officially TB free (OTF) herds from life-long restrictions, the option of private interferon-gamma blood testing (paid for by the animal owner) is available to cattle keepers, subject to securing prior approval from APHA.
Resolved IRs in TB restricted herds undergoing government funded mandatory gamma testing will automatically be included in any whole herd testing as long as they are over six months of age, therefore private gamma testing is not necessary in these cases. The blood sample must be collected (at the keepers expense or as part of a government-funded test) on or after the injection date (day 1) of the clear IR re-test.
If a resolved IR tests negative to the gamma test, movement restrictions on the animal are lifted and it can move freely, unless whole herd movement restrictions apply. Cattle keepers wishing to take up private gamma testing should contact their private vet who needs to secure permission from APHA to carry out the test. It is important to note that if the test result is positive the animal is compulsorily slaughtered (with compensation paid), movement restrictions are placed on the whole herd (if not already in place) and the standard TB breakdown procedures followed.
Identification of resolved IRs
It is the cattle keeper’s responsibility to ensure resolved IRs are restricted for life to the holding in which they were found. Although not a mandatory requirement, Defra recommends that such animals are physically identified to prevent accidental movement off the holding.
This could be achieved by using a management tag or freeze branding, and/or marking the animal’s passport.
Restriction of resolved IRs
Resolved IRs are automatically restricted following their clear re-test, and keepers receive a restriction notice in the post. Resolved IRs are restricted for life to the holding in which they were found, and this holding must have a permanent County Parish Holding (CPH) number. If a resolved IR is residing at temporary grazing when it re-tests clear, it is restricted to the permanent CPH associated with the temporary grazing. Once the resolved IR moves back to the permanent CPH, it is restricted to that CPH and cannot move back to a temporary CPH.
All IRs in the HRA and Edge Area (and in TB breakdown herds in the LRA) that have a negative result on re-testing remain restricted for the rest of their life to the holding in which they were found. The only permitted off movements for such animals are to slaughter, either directly or via an Approved Finishing Unit.
Resolved IRs have a significantly higher likelihood of becoming reactors than clear tested animals, and as such present an increased risk of spreading TB. Restricting resolved IRs for life to the holding in which they were found prevents transfer of this risk to other herds.
Slaughtering all IRs would be disproportionately costly. Increased numbers of TB-free cattle would be slaughtered resulting in additional herds being unnecessarily placed under movement restrictions. Accepting that the risk can never be completely eliminated, the policy aims to reduce the risk to an acceptable level with the resources available to the government.
No, not necessarily. Keepers can send an IR to slaughter privately, before it is re-tested, under licence from APHA. Keepers wishing to privately slaughter an IR must contact APHA to discuss the implications and obtain a licence to move the animal to slaughter.
It is the keeper’s responsibility to ensure resolved IRs are restricted for life to the holding in which they were found. If a keeper intends to retain resolved IRs in their herd it is advisable, but not mandatory, to physically identify them to prevent their accidental movement off the holding. This can be achieved by using a management tag or freeze brand and/or marking the animal’s passport. It is also advisable to keep a record of any resolved IRs in the herd register.
A restriction notice is issued by APHA explaining the conditions of the restrictions and the keeper’s obligations.
Potentially, yes. Cattle keepers can commission interferon-gamma blood testing of resolved IRs at their own cost. The keeper must first seek permission from APHA through their private vet. The blood sample must be collected on or after the injection date (day 1) of the clear IR re-test. If the resolved IR tests negative to the gamma test, the animal is free to move off the holding, unless it is subject to any other whole herd movement restrictions. If the animal tests positive, it is compulsorily slaughtered (with compensation paid), movement restrictions are applied to the whole herd (if not already in force), and standard TB breakdown procedures followed.
Animals less than six months of age are excluded from gamma testing as their immune systems are still developing and this can interfere with the test, leading to false positive results. If a resolved IR is too young for a gamma test, the keeper may apply to APHA to defer the test until the animal becomes old enough. The keeper or their private vet must contact APHA to discuss the situation and all cases are assessed on an individual basis.
A resolved IR in a TB-restricted herd undergoing government funded mandatory gamma testing will automatically be included in any whole herd testing as long as it is over six months of age. If the resolved IR tests negative to the gamma test then the restrictions on the animal are lifted, though it would continue to be subject to whole herd movement restrictions. If the resolved IR tests positive to the gamma test it is compulsorily slaughtered with compensation paid, just like any other reactor.
Yes. Resolved IRs are permitted to move to slaughter either directly or via an Approved Finishing Unit (AFU) under a licence issued by APHA. Movements of resolved IRs to AFUs can occur directly or via a TB dedicated sale (orange market). Movements of resolved IRs to slaughter can occur directly or via an approved slaughter gathering. Please contact APHA if you are considering this option as you need a licence.
Temporary CPH (tCPH)
Resolved IRs found at a tCPH are restricted for life to the permanent CPH associated with the tCPH. The resolved IR is only permitted to move back to the permanent CPH associated with the tCPH, or to slaughter either directly or via an AFU. Once back at the permanent CPH, the animal is restricted for life to that CPH.
Temporary Land Association (TLA)
If a resolved IR is found at a TLA it is restricted to the permanent CPH associated with the TLA. Subsequent movements of the resolved IR to the TLA are permitted, as by definition the land falls within 10 miles of the permanent CPH. For more information on livestock movements, tCPHs and TLAs, see the Defra guidance.
If a resolved IR is found whilst at common grazing it is restricted for life to the keeper’s home holding which must have a permanent CPH number. The resolved IR is not permitted to move to common grazing again because of the increased risk it potentially presents to other herds that use the common land.
No. Resolved IRs are restricted to the holding in which they were found for the rest of their life and cannot move off to agricultural shows.
Yes. Resolved IRs can move off the holding for veterinary treatment under a licence issued by APHA. After treatment the animal must return directly to the home holding or to slaughter.
APHA carries out percentage checks of resolved IRs to ensure that they remain restricted for life. Non-compliances are referred to the relevant Local Authority for investigation and any enforcement action they deem appropriate.
- Clegg, T. A. et al. Shorter-term risk of Mycobacterium bovis in Irish cattle following an inconclusive diagnosis to the single intradermal comparative tuberculin test; Preventive Veterinary Medicine 102(4):255-64
- Clegg, T. A. et al. Longer-term risk of Mycobacterium bovis in Irish cattle following an inconclusive diagnosis to the single intradermal comparative tuberculin test; Preventive Veterinary Medicine 100 (3-4):147-154
- Bovine TB epidemiology and surveillance in Great Britain, 2018, APHA
- May E, Prosser A, Downs S. H, Brunton L. A. Exploring the risk posed by animals with an inconclusive reaction to the bovine tuberculosis skin test in England and Wales; Veterinary Science 2019, 6(4), 97