Frequently Asked Questions

Skin Test

Q1. Is it true that skin test positive animals that show no signs (lesions) of TB in their organs at post-mortem examination (known as ‘NVL’ or ‘no visible lesion’ animals) have never had TB?

A1. No. When TB reactors are found on the tuberculin skin test, it is very likely that those cattle are infected with bovine TB, even if no visible TB lesions are found at post-mortem meat inspection.

This is because the skin test used in the UK and Ireland is very specific, meaning it is extremely unlikely to generate a false positive result (only 1 false positive for every 5,000-6,000 TB-free cattle tested with the standard test). The skin test can also find TB long before infected cattle have developed clinical signs that would be noticed by an experienced stockman or a vet.

Reactors to the skin test may therefore not have any visible lesions because they are either in the early stages of the disease, or the lesions are too small to be detected by the naked eye. TB lesions can be large and clear to the naked eye as in this image, or they can be extremely small (microscopic) and difficult for a meat inspector to detect during a relatively quick visual inspection of the carcase in a busy slaughter line. Often, even if no visible lesions are found at the slaughterhouse, had the carcase been more carefully examined in a laboratory, microscopic lesions could have been detected. But even if no lesions can be detected a reactor animal is still very likely to be infected with TB.

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However, whilst non-lesioned reactors can be infectious, animals that are found to have visible lesions are more likely to be frequently excreting TB bacteria and present a higher infection risk to other cattle than the non-lesioned animals. Therefore it is preferable to catch the disease in its earlier stages before visible lesions have had an opportunity to develop, and remove those reactors from the herd before they have had the opportunity to infect other animals and cause a more serious TB herd breakdown.

Managing TB

Q2. What happens if I have a TB reactor in my herd? Does this mean I can’t then trade?

A2. Your herd will be placed under movement restrictions. This doesn’t necessarily mean you can’t trade but, to reduce the risk of disease spread, the options available to you may change (see question 5 for more information). Be aware, no movements are allowed onto new breakdown farms and movements off will be limited until the first short interval test has been completed.

 

Q3. How long will I be under movement restrictions after my first positive test?

A3. This depends on the circumstances, including the extent and nature of the breakdown and the area in which your holding is located. It will also depend upon whether further reactors are found at subsequent tests. However, in all cases herd restrictions will be in place for at least 60 days from the date the reactors are found.

 

Q4. What TB diagnostic tests are used and is there a choice of which test can be used?

A4. The primary screening test for TB in cattle in Great Britain is the tuberculin skin test. The Gamma Interferon blood test is a supplementary TB test that may be used by APHA in some breakdown situations to increase the chance of identifying infected animals in a herd.

 

Q5. Will I be compensated for stock that are found to have TB and how much will I receive?

A5 Compensation is paid to owners of cattle the Government requires to be compulsorily slaughtered for TB control purposes. Compensation is determined primarily through table valuations, based on average market prices, which are updated and published monthly by Defra.

 

Q6. What routes of sale do I have for stock when under restriction?

Q6. Cattle can only move from TB breakdown herds under licences issued by APHA. Routes of sale when under restriction include to slaughter (either directly or via an approved slaughter gathering or collection centre), Approved Finishing Units (AFUs), Orange Markets or other restricted farms.

 

Q7. My neighbour has just gone down with TB. What does that mean for me?  

A7. Depending on the nature (e.g. post-mortem evidence of disease found) and location of the TB incident your herd may be subject to a TB test. Also, if you have purchased stock from your neighbour a ‘tracing’ test of those animals may be required.

 

Q8. Are there any practices that could help me get clear of the restriction?

A8. Good biosecurity can help to reduce the risk of TB spread within your herd (as well as other disease transmission risks) and any risk of further transmission from wildlife. Guidance on biosecurity can be found on the TB Hub.

 

Q9. If I have two farms, is there any advantage of running them as entirely separate holdings (i.e. two holding numbers) in the event of a TB breakdown?

A9. There are many factors to take into account when considering this possibility. One consideration is the fact that running farms as entirely separate holdings (i.e. with different CPH numbers and equipment and no SOA or CTS links between them) could mean that both aren’t automatically shut down in the event of a breakdown on one of them. However, APHA will consider any risks of transmission on the non-breakdown farm and, if judged necessary, restrictions would be extended to that holding. There are also disadvantages with operating separate holdings, including the need for cattle moving between the two holdings to be pre-movement tested and all movements recorded with BCMS.

 

Q10. Is there an advantage to setting up an Isolation Unit on my farm to get rid of animals sooner in case the main herd fails?

A10. Isolation units within a holding are no longer permitted. However, isolation and testing of TB restricted cattle from a single source on a separate, unrestricted holding is possible, subject to assessment and approval by APHA. Cattle in that Unit would then be subject to TB testing at 60-day intervals. Restrictions may be lifted following two clear, consecutive 60-days tests and provided the last test is at least 120 days after the date that the unit was closed.

 

Q11. If a cow fails the TB test, will her calf be taken too?

A11. Calves from reactor animals are not routinely taken. However APHA will assess the risks to the calf following post-mortem examination of the reactor cow. If the risk to the calf is deemed to be high, for example if the cow had TB lesions in the udder, then it will be taken as a direct contact. Compensation would be paid for the calf. In reality this is a rare event.

Herd health

Q12. Do liver fluke (infestation with Fasciola hepatica) and the use of flukicides affect the performance of the tuberculin skin test in the field?

A12. There is no conclusive evidence to support this hypothesis at present and there is no advice with regard to modifying the interpretation of the SICCT test in the context of evidence of liver fluke infection in a specific herd. Nevertheless, farmers are advised that, where possible, medicines and routine veterinary treatments (including wormers) should not be given to cattle on the first day of the tuberculin skin test, or shortly before a test. If possible wait until the test results are read on the second day and animals have passed the test.

 

Q13. Is TB testing compromised by the presence of Johne’s disease?

A13. Potentially. Infection of cattle with Mycobacterium avium subspecies paratuberculosis (the agent of Johne’s disease) and vaccination against the disease can cause cross reactivity to the skin and interferon-gamma tests for bovine TB.


Q14. What is the TB implication of BVD (Bovine Viral Diarrhoea) infection in herds?

A14. It is possible that any infective agent that suppresses an animal’s immune response mechanism such as occurs in cattle when infected with BVD virus, will increase the susceptibility to and ability to fight other infectious diseases such as TB. For instance, concurrent TB and other infections are frequently seen in people infected with HIV, but there has been limited work to demonstrate a similar risk for cattle infected with BVD virus.

Genetic Resistance

Q15. Are some cattle breeds more resistant to bovine TB than others? Is it possible to breed cattle that are resistant to M. bovis infection?

A15. There is anecdotal evidence pointing to differences in resistance to infection with M. bovis between European cattle breeds and zebu (Bos indicus) regions.

In the UK, there is no clear evidence of differences between breeds in terms of susceptibility to bovine TB. While there is evidence that dairy farms are more likely to experience a breakdown than beef farms, this is not necessarily due to breed differences.

However, pedigree analyses funded by the Government have shown evidence of genetic variation to bTB susceptibility within Holstein-Friesian dairy cattle in the UK and similar evidence exists from Ireland and NI.  However, the actual impact (if any) of genetic selection for bTB resistance on the incidence of bTB in cattle has yet to be determined.

Homeopathy

Q16. Will supplementing cattle feed with homeopathic medicine, trace elements and/or selenium prevent a TB outbreak?

A16. No. There is no proven relationship between trace element supplementation and decreased susceptibility to bovine TB. As a general rule, cattle should be fed a balanced nutritional diet according to their production status and any deficiencies of trace elements in cattle rations should be corrected as a matter of good husbandry practice.

Badgers

Q17. Can the badgers in a sett be proven to have TB by testing the soil and faeces?

A17. Detection of M. bovis directly from badger excretions is difficult, largely because of the low levels and intermittent nature of excretion of M. bovis by infected animals. A number of methods have recently been independently evaluated by APHA and the Royal Veterinary College, but none of them has proven to be sufficiently specific and sensitive at the sett level for use as tool in TB surveillance of badger populations or to support selective culling of M. bovis-infected social groups.

 

Q18 Isn’t it relatively easy to identify TB infected badgers on the basis of appearance and behaviour?

A18. No. It is not possible, as with cattle, to identify infected badgers on the basis of appearance, behaviour or clinical signs. Only in the very late stages of disease do animals show clinical signs and these are non-specific and may reflect diseases other than TB.

 

Q19. Does growing maize encourage badgers and increase the likelihood of a TB breakdown in your herd?

A19. There is anecdotal evidence that badgers are attracted to maize and maize silage. In areas where maize is grown it often forms part of their diet. However, badgers can, and do, eat a wide variety of foods encompassing plants, invertebrates and small vertebrates and there is no evidence to suggest that reducing the amount of maize grown and replacing it with grass silage or other crops can reduce badger populations (and the incidence of TB in cattle) to an extent that would justify what would be significant changes to farm management practices.