Bovine TB: Consultation on revised guidance for licensing badger control areas Response from the Zoological Society of London

 

Bovine TB: Consultation on revised guidance for licensing badger control areas

Response from the Zoological Society of London

The Zoological Society of London (ZSL) has a long history of scientific engagement with the management of bovine tuberculosis (TB) in British cattle and wildlife. ZSL is both a scientific research institution and a conservation NGO. As such, for this consultation we have commented on both the scientific and the conservation issues relating to the expansion of

badger culling to a larger number of areas of England. ZSL does not support the government’s policy of culling badgers in an attempt to control cattle TB. While recognising that badgers can and do transmit TB to cattle, we note

that the best estimates indicate that approximately 6% of TB-affected cattle herds become

infected from badgers, with the remaining 94% acquiring infection from other herds1. We

therefore consider the management of cattle-to-cattle transmission to have the highest

priority for TB control. We recognise that TB eradication requires clearing infection from the

badger population as well as from cattle herds, but suggest that for this purpose vaccination

(which reduces TB prevalence in badger populations2,3) is more promising than culling

(which consistently increases TB prevalence in UK badger populations4-6). Badger culling has

the capacity to increase cattle TB as well as reducing it7,8, making it an unsatisfactory tool for

TB control. Primary analyses have so far revealed no significant reduction in cattle TB from

farmer-led culls9. Moreover, large-scale badger culling entails killing thousands of members of

a protected species which plays an important role in farmland ecosystems10-12.

In addition to these general concerns, ZSL has four specific concerns about Defra’s

proposal to accelerate the recruitment of large badger culling areas.

(1) Impact on the assessment of whether farmer-led culling changes cattle TB

Recruiting cull areas more rapidly would compromise efforts to assess whether badger

culling is reducing cattle TB as intended. Government scientists are assessing the effects of

culling on cattle TB using a “stepped wedge” study design, in which areas which have not yet

been culled serve as comparison areas for the cull areas9. If culling has the intended effect,

these not-yet-culled areas would be expected to show higher cattle TB incidence than areas

where culling has started. Recruiting cull areas more rapidly would curtail each area’s time as

a comparison area, making it more difficult to determine whether or not culling is

contributing to TB control. If farmer-led culling was certain to be a cost-effective control

measure, and if additional culls could be implemented without compromising existing culls,

then reducing farms’ time in the “not-yet-culled” comparison areas would accelerate TB

control. However, to date primary analyses have revealed no significant evidence that culling

is reducing cattle TB9, and secondary analyses on preliminary data are not robust enough to

yield policy conclusions13. Limiting the statistical power of further analyses by culling the

comparison areas might thus leave farmers, government, and taxpayers without reliable

evidence to evaluate the cost-effectiveness of a control tool which is strategically important,

but also costly and controversial. Moreover, a lack of evidence that culling is reducing cattle

TB makes it increasingly difficult to justify the destruction of a protected species, in the eyes

of the law (which requires that culls be conducted “for the purposes of preventing the spread of

disease”14), and in the eyes of the public who mostly oppose badger culling15.

(2) Impact on review of Defra’s TB policy

Defra has recently commissioned a scientific review of its TB control policy, which is

scheduled to report in September 2018. Defra has stated publicly that this review will

consider the future role of badger culling in Defra’s TB strategy16. However, any new cull

licences granted in 2018 would have to be issued before completion of the scientific review, to

avoid forcing culls to operate entirely in the late autumn when trapping success is typically

low17. Issuing large numbers of new licences just before the review is published would prejudge

the outcome of the review, constraining its ability to influence Defra’s TB policy, and

raising questions about Defra’s commitment to the principle of the review.

(3) Impact on the implementation of other TB control tools

Defra ministers have repeatedly stated the need to deploy “every tool in the box” to

combat TB. Consistent with its remit of stewarding the natural environment while overseeing

food production, and its long-term plan of reforming farm subsidies to reward wildlifefriendly

farming, Defra would be expected to explore ways to promote the coexistence of

cattle and wildlife. Badger vaccination in particular has been proposed as a TB control tool

which is more sustainable, cheaper, and more publicly acceptable than culling. However,

vaccination is increasingly sidelined in Defra’s TB policy, as culls are proposed or

implemented throughout the high-risk, low-risk and edge areas. Defra’s vision of culling

badgers across the high-risk area, which covers the entire western side of England, would

remove the option of implementing or even exploring badger vaccination as a cheaper, less

controversial, and potentially more sustainable approach.

(4) Environmental impact

Badger culling has impacts on farmland ecosystems10-12, as would be expected from the

removal of the largest native carnivore remaining in Britain. Defra’s consultation implies that

the environmental impact of badger culling is not a concern because culling does not cause

local extinction of badgers. However, Natural England formerly advised limiting the

geographical extent of badger culling on conservation grounds18, noting that “reducing the

badger population to the extent and on the scale permitted under this policy has not previously

been sanctioned for any protected native mammal species in modern times”.

Concerns about environmental impact do not relate only to the risk of localised badger

extinction (i.e. a 100% reduction in badger density). Multiple ecological consequences were

evident from a 70% reduction in badger density in the Randomised Badger Culling Trial

(RBCT)10-12, and the proposed policy change is likely to have greater impacts because the

current and proposed culls are both more extensive and more prolonged. Defra’s original plan

was to recruit up to 10 areas per year, with each area being culled over four successive years

and then allowed to recover. This arrangement would have meant that, over time, some areas

would be newly culled while others would be recovering from culling. However, Defra is now

encouraging culls to be continued indefinitely after the initial four years. Moreover, the

establishment of multiple contiguous large-scale culling areas means that cull zones now

encompass a greater diversity of ecological settings than were sampled in the RBCT, and sites

within the cull zones are increasingly distant from the edges. The ecological consequences of

reducing badger densities over huge geographical scales and prolonged periods are thus

likely to be greater than those documented in the RBCT, and impacts may occur which were

either not investigated or not detectable in the RBCT. Impacts of extensive badger culling on

nature conservation, including impacts on other protected species, thus need to be seriously

considered.

On a broader scale, there may be wider environmental consequences of expanding

badger culling to the extent envisioned. Defra ministers are planning to restructure farm

subsidies post-Brexit to reward environmentally-friendly farming. Simultaneously

encouraging widespread culling is inconsistent with this plan and sends a mixed message to

both farmers and the public.

On a still broader scale, Defra is seeking to portray Britain as a world leader in wildlife

conservation, for example introducing tough new laws on ivory trading and hosting the 2018

conference on the Illegal Wildlife Trade. It may be more difficult for the UK to encourage

other, poorer, countries to find ways to coexist with dangerous wildlife such as elephants and

tigers, while itself failing to even explore sustainable ways for its own farmers to coexist with

what is essentially a large weasel.

Literature Cited

1 Donnelly, C. A. & Nouvellet, P. The contribution of badgers to confirmed tuberculosis in cattle in high incidence areas in

England. PLoS Currents Outbreaks, doi:doi: 10.1371/currents.outbreaks.097a904d3f3619db2fe78d24bc776098.

(2013).

2 APHA. APHA report of examination for Mycobacterium bovis in badgers found dead within the Welsh Government Intensive

Action Area (IAA) (OG0145/TBOG0146). (http://gov.wales/docs/drah/publications/170508-bovine-tb-badger-founddead-

survey-report-4-en.pdf, 2016).

3 Carter, S. P. et al. BCG vaccination reduces risk of tuberculosis infection in vaccinated badgers and unvaccinated badger

cubs. PLOS One 7, e49833, doi:10.1371/journal.pone.0049833 (2012).

4 Woodroffe, R. et al. Culling and cattle controls influence tuberculosis risk for badgers. Proceedings of the National

Academy of Sciences of the United States of America 103, 14713-14717 (2006).

5 Woodroffe, R. et al. Bovine tuberculosis in cattle and badgers in localised culling areas. Journal of Wildlife Diseases 45,

128-143 (2009).

6 Bielby, J., Donnelly, C. A., Pope, L. C., Burke, T. & Woodroffe, R. Badger responses to small-scale culling may compromise

targeted control of bovine tuberculosis. Proceedings of the National Academy of Sciences of the United States of America

111, 9193-9198, doi:10.1073/pnas.1401503111 (2014).

7 Donnelly, C. A. et al. Positive and negative effects of widespread badger culling on cattle tuberculosis. Nature 439, 843-

846 (2006).

8 Donnelly, C. A. et al. Impact of localized badger culling on TB incidence in British cattle. Nature 426, 834-837 (2003).

9 APHA. Report on the incidence of bovine tuberculosis in cattle in 2013-2016 – Three years’ follow-up in areas of Somerset

and Gloucestershire and one year of follow-up in Dorset of industry-led badger control.

(https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/643492/tbbadger-

control-third-year-analysis.pdf, 2017).

10 Trewby, I. D. et al. Experimental evidence of competitive release in sympatric carnivores. Biology Letters 4, 170-172,

doi:10.1098/rsbl.2007.0516 (2008).

11 Trewby, I. D. et al. Impacts of Removing Badgers on Localised Counts of Hedgehogs. Plos One 9, 4,

doi:10.1371/journal.pone.0095477 (2014).

12 CSL. The ecological consequences of removing badgers from the ecosystem.

(randd.defra.gov.uk/Document.aspx?Document=ZF0531_6288_FRP.doc, 2007).

13 Brunton, L. A. et al. Assessing the effects of the first 2years of industry-led badger culling in England on the incidence of

bovine tuberculosis in cattle in 2013-2015. Ecology and Evolution 7, 7213-7230, doi:10.1002/ece3.3254 (2017).

14 UK Parliament. Protection of Badgers Act. (Her Majesty's Stationery Office

http://www.opsi.gov.uk/acts/acts1992/Ukpga_19920051_en_1.htm - end, 1992).

15 YouGov. Two years on, badger cull remains unpopular. (https://yougov.co.uk/news/2014/09/11/two-years-badgercull-

remains-unpopular/, 2014).

16 Doward, J. Badger cull faces review as bovine TB goes on rising. The Observer,

https://www.theguardian.com/environment/2018/mar/2004/badger-cull-government-review-bovine-tb-inquiry

(2018).

17 Tuyttens, F. A. M. et al. Differences in trappability of European badgers Meles meles in three populations in England.

Journal of Applied Ecology 36, 1051-1062 (1999).

18 Natural England. The impact of culling on badger (Meles meles) populations in England and measures to prevent their

‘local disappearance’ from culled areas. http://www.gloucestershirewildlifetrust.co.uk/sites/wtmain.

live.drupal.precedenthost.co.uk/files/Natural_England_-_Advice_to_Defra_-_Control_of_Badgers_-_Jul_11_-

 

_Redacted.pdf (2011).