A TB breakdown is considered persistent when the herd reaches 18 months under movement restrictions. The Animal & Plant Health Agency (APHA) deploys a range of interventions to help clear these herds of TB.
Bovine TB causes considerable cost, stress, and frustration for farming communities, particularly for farmers with herds under long-term movement restrictions. Persistent breakdowns are also resource intensive for APHA to manage and account for a significant proportion of Defra’s spend on TB testing and compensation payments. Since 2019 there has been an encouraging and welcome reduction in the number of persistent breakdown herds in England, which Defra wants to accelerate further .
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Managing persistent TB breakdowns
Communications to farmers
The flow diagram below describes APHA’s processes and communications to keepers of TB breakdown herds before and after they become persistent. When a herd reaches 12 months under movement restrictions, APHA will write to the keeper to signpost them to sources of advice and support and explain what further actions may be taken if the breakdown becomes persistent. When a breakdown herd reaches 18 months under movement restrictions, APHA will write to the keeper again to explain that additional control measures may be applied to resolve the breakdown.
TB breakdown herd reaches 12 months under movement restrictions
APHA sends a letter notifying the keeper of actions that may be taken if the TB breakdown becomes persistent
TB breakdown herd reaches 17 months under movement restrictions
APHA reviews the TB breakdown and the need for a mandatory interferon-gamma blood test
Mandatory interferon-gamma test scheduled at 18 months under restrictions
TB breakdown herd reaches 18 months under movement restrictions
APHA sends a letter notifying the keeper of actions that may be taken now that the TB breakdown is persistent
Additional control measures for persistent TB breakdowns
The flow diagram below summarises additional control measures that may be implemented by APHA and others to try to resolve persistent TB breakdowns. Not all of these herds will have every intervention applied as each breakdown is different and requires a bespoke approach. The ultimate aim is to clear long-term restricted herds of TB infection and maximise the likelihood of them staying clear.
Enhanced disease investigation
An APHA vet may carry out an enhanced disease investigation to identify the most likely risk factors for persistence of TB infection in the herd. This will start with a desk-based review of information related to a breakdown and may involve a visit to the farm.
The enhanced disease investigation considers:
- The TB situation in the surrounding area
- Management of the breakdown herd and biosecurity
- Previous TB breakdowns (if applicable) and the most likely origin of the current breakdown
- Summary of the current breakdown including history of TB reactors
- Potential reasons for persistence of TB infection in the herd e.g. undisclosed infection in the herd, infection from wildlife, repeated purchases of infected/susceptible cattle, contact with neighbouring cattle as a source of sustained infection etc.
- Most likely reason(s) for persistence of TB infection in the herd with considered likelihood and supporting evidence
- Recommended actions to address the most likely reasons for persistence of infection within the herd
Following the enhanced disease investigation, the APHA vet may have a meeting with the farmer and (if possible) their private vet to review the breakdown, discuss possible additional control measures and agree a timescale for implementation of an action plan. The APHA vet will signpost the farmer to further sources of information, advice and support, and recommend a free visit by the TB Advisory Service (TBAS).
Removal of animals as direct contacts
A direct contact (DC) is an animal that, although has not tested positive for TB, has been in contact with known infected animals and is slaughtered for disease control purposes, with compensation paid.
In persistent TB breakdown herds, animals may be removed by APHA as DCs, including inconclusive reactors (IR) before they are re-tested. Alternatively, you can consider private slaughter of IRs or a private gamma test to provide additional information about their true infection status and help inform decisions about their management. You can discuss the options for management of IRs with your private vet and APHA.
Skin testing at severe interpretation
The tuberculin skin test can be interpreted at either standard or severe interpretation. Interpreting the test at severe interpretation involves lowering the cut-off point for an animal to be classified as a reactor. What this means in practice is that some animals considered inconclusive reactors at standard will become reactors at severe interpretation. APHA may decide to test a persistent breakdown herd using only severe interpretation to increase the sensitivity of testing thereby maximising the opportunity to identify and remove infected animals. This is applied regardless of the post-mortem examination results of any reactors disclosed, which usually influences the interpretation of the subsequent short interval test.
Supplementary blood testing
Supplementing the tuberculin skin test with more sensitive blood tests also aims to maximise detection of infected cattle in a persistent breakdown herd. Blood tests can identify a different cohort of infected animals to the skin test, as well as infected animals that simply fail to respond to the skin test.
Mandatory interferon-gamma blood testing is applied by APHA to persistent breakdown herds where repeat skin testing has failed to clear TB infection. When a TB breakdown herd reaches 17 months under movement restrictions APHA will assess the need for a gamma test and, if appropriate, schedule a test to be carried out when the breakdown becomes persistent. Farmers are notified of the requirement for a gamma test in the letters that they receive when their herd reaches 12 and 18 months under movement restrictions. A separate letter is also sent to keepers notifying them of the arrangements for a herd gamma test if required. Some herds may have already undergone mandatory or discretionary gamma testing before the breakdown became persistent, and this is considered when APHA completes an assessment at the 17 month stage.
If the APHA vet thinks that confirmed Johne’s disease (caused by Mycobacterium avium subspecies paratuberculosis, MAP) in the herd and/or recent vaccination against the disease is interfering with the skin and/or gamma tests, targeted use of a flexible-extended gamma test option can be considered if certain criteria are met. In herds co-infected with M. bovis and MAP, the animal’s specific response to bovine tuberculin may be masked by a MAP-driven increase in the animal’s response to avian tuberculin. This leads to a false negative result, i.e. the animal tests negative but is actually infected. The flexible-extended gamma test uses M. bovis-specific antigens that are not expressed by MAP in addition to the conventional avian and bovine tuberculins (the same as those used in the skin test). This means that the flexible-extended format of the test provides additional sensitivity in herds co-infected with M. bovis and MAP.
IDEXX antibody testing
The M. bovis IDEXX antibody test is used by APHA in persistent breakdown herds as a third line test where repeated skin testing and use of the gamma test has already occurred. The test is used in exceptional circumstances, and eligibility is determined on a case-by-case basis. The IDEXX antibody test can (unlike the gamma test) be applied to cattle of any age, so it may be useful for targeted testing of cattle under six months old where indicated. Where the IDEXX antibody test is instructed by APHA and carried out according to Defra policy, compensation is paid for the removal of any test-positive animals as normal.
Private blood testing
In England only, the IDEXX antibody test is also available for private use at the keeper’s expense, however prior permission from APHA must be obtained by the private vet. Before IDEXX testing is deployed, the herd (or management group) must have undergone gamma testing if required under current Defra policy.
All privately-funded IDEXX test results must be shared with APHA and any test-positive animals must be slaughtered before movement restrictions can be lifted at the end of the breakdown. Compensation is not paid for any test-positive animals where the test was privately-funded, and the removal and slaughter costs are the responsibility of the keeper.
Non-approved tests (e.g. the Enferplex TB test) and non-validated tests can be used in England under Defra’s protocol for exceptional private use, available on the APHA Vet Gateway. Farmers considering additional, voluntary TB testing of their animals should discuss the available options with their private vet and APHA.
Implementation of biosecurity measures
APHA, your private vet and the TB Advisory Service (TBAS) can advise you on implementing biosecurity measures to help protect your herd from TB. There is lots of practical guidance on the TB hub, including case studies and biosecurity information sheets describing measures that you can take on-farm to minimise indirect and direct contact between cattle and badgers. Completing a wildlife survey of the farm and/or installing cameras can help identify areas that would benefit from increased biosecurity.
TB Advisory Service visit
Keepers of persistent breakdown herds can take advantage of free, bespoke advice from the TB Advisory Service (TBAS). Contact TBAS to arrange an on-farm visit where one of their trained Veterinary Advisers will provide tailored advice on implementing practical, cost-effective biosecurity measures. They will also discuss trading options and contingency planning to lessen the impact of long-term movement restrictions on the herd.
Telephone: 01306 779410
If you have a TBAS visit, it’s of benefit to share the report produced with your private vet (if they did not complete the visit). It’s also helpful to provide your consent to TBAS when asked, to enable them to share your visit report with APHA. The recommendations made by TBAS can be incorporated into an action plan developed by you, APHA and/or your private vet.
Other sources of advice and support
Your private vet can advise you on TB control, herd health and welfare, and contingency planning whilst under long-term movement restrictions. If you are a farmer experiencing difficulties with your mental or physical health, finances or family life due to a TB breakdown in your herd, visit our support organisations page for services that can help.
Implementation and monitoring of the action plan
If an APHA vet completed an enhanced disease investigation, they will have developed an action plan with you, and ideally your private vet. If you have received a visit from TBAS, their recommendations can also form part of the action plan. It’s important to agree a realistic timescale for implementation of the action plan and review progress along the way. Your private vet, APHA and TBAS can all provide advice and support to help you implement the action plan and ultimately achieve TB-freedom for your herd.
If APHA has not developed an action plan for your herd then you may wish to make one of your own with your private vet. An action plan template and guidance document is available below as a resource to help you and your vet.