Setting the minimum and maximum numbers in badger cull areas in 2024: advice to Natural England
Published 16 October 2024
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Overview
Natural England is the competent authority for badger control licensing for the purpose of preventing the spread of bovine TB. It is a requirement of the Guidance and the licences to set a minimum number in advance of each year’s cull in an authorisation letter that is issued to each cull company once the licensing authority is satisfied that the cull company’s preparations, planning and funding are sufficient to deliver a successful cull. The purpose of setting a minimum number under the current licence is to ensure that the cull company delivers the required level of population reduction in order to achieve the expected benefits in controlling bovine TB.
This advice to Natural England sets out the approach for estimating the badger population in the cull areas in 2023 and the minimum number of badgers to be removed and the minimum number of badgers that need to be vaccinated for a site in an Edge Area county to qualify for a no-cull zone.
The minimum number is intended to achieve a 70% reduction of the population relative to the initial starting population. The culling objective is for no more than 30% of the starting population to remain on conclusion of the cull. The 70% target is derived from the Randomised Badger Control Trial (RBCT) where it was estimated that the culls achieved a mean of 70% control of the starting populations across the 10 areas (Woodroffe et al., 2008), which resulted in disease reduction benefits for the cattle herds in those areas.
Culling also needs to “not be detrimental to the survival of the population concerned” within the meaning of Article 9 of the Bern Convention on the Conservation of European Wildlife and Natural Habitats. For that purpose, Natural England set a maximum number of badgers to be removed from the licensed area.
The approach to setting the minimum and maximum numbers was published by Defra in 2014 to 2023, in advice to Natural England.
The estimate of population size must relate to the whole culling area, including any land within that area on which no culling is planned to take place. Any population estimate will have some degree of uncertainty which leads to an interval around the population estimate within which the true population is likely to lie. However, operating with uncertainty does not prevent an effective cull from being carried out, as shown during the RBCT culls, where no minimum numbers or targets were set.
This advice is divided into three sections.
- Section A covers the areas where Supplementary Badger Culling (SBC) is taking place in 2024
- Section B covers the areas where culling began in 2021 and 2022
- Section C covers concluding remarks affecting all of the areas
To ensure that the special status of the Low Risk Area (LRA) remains, it is vital that we deal swiftly and decisively with any incursion of TB which involves both cattle and badgers. As such, adaptive management, where assessment of the evidence and consideration of a range of options takes place annually, is required. This is so that the most effective course of action is taken to enable eradication within the shortest timescale. The Chief Veterinary Officer (CVO) advises that eradication can only be achieved in an area if infection present in the badger population is addressed alongside that in the cattle population.
This year in the Low Risk Area, culling will begin in Area 73 – Cumbria and continue in Area 54 – Lincolnshire. Area 32 – Cumbria continues to have badger vaccination across the whole area.
Section A: Areas 4 to 9, Areas 33 to 43 and Areas 45 to 53
In 2024, Areas 4 to 9 and Areas 33 to 43 will continue Supplementary Badger Control (SBC). Areas 45 to 53 inclusive will begin SBC.
Both minimum and maximum numbers of badgers to be removed are required in order to sustain the benefits of licensed badger control while avoiding local extinction. As in previous years, for SBC areas 36% of the year one cull total is set as the baseline and the minimum and maximum numbers are set equidistant above and below the baseline so that the difference between them is equivalent to 25% of the pre-cull population. The minimum and maximum numbers are listed in Table 1 of Annex A.
This approach will be kept under review as culling in contiguous areas and the larger size of the cull areas could affect the relative levels of immigration and reduce the comparability of cull returns to those in the RBCT. Therefore, the amount of effort deployed by the cull companies and its spatial distribution will continue to be monitored given the uncertainty in the size of the remaining badger population.
Area 3 ceased culling operations after completing the fifth and final year of their SBC licence in 2023. Areas 11 to 31 inclusive have now also ceased culling operations after completing the second and final year of their SBC licence in 2022 and 2023. Area 10 elected to cease after completing four years of their five-year SBC licence in 2023. Area 44 elected to not apply for an SBC licence.
Section B: Areas 55 to 72
As several hundred badgers have been removed from these areas in previous culls, methods based solely on an un-culled population are no longer appropriate. Instead, as in previous years, surveys of the number of active setts were used to estimate the current population.
In order to ensure that accurate assessments of sett activity were available to provide robust evidence to inform an estimate of the population and minimum numbers, all cull companies were instructed to carry out a thorough sett survey programme.
As described in detail in the 2015 advice to Natural England, the population can be estimated by multiplying the number of active setts by the number of badgers per active sett.
As described in 2018, the starting population is estimated by reducing the estimate of the population at the start of year two by one-sixth, to account for 20% population growth in the intervening period, and adding the number culled in year one. The minimum and maximum numbers are then calculated as in previous years, see Table 2 in Annex A. Given the overall uncertainty associated with the methods and the range (lower to upper limits), we consider that it is still more prudent to manage the uncertainty by defining a realistic minimum number that aims to achieve the desired level of population reduction to secure the anticipated disease control benefits than to define it too high, with a risk of removing too many badgers.
Areas 55, 58, 59, 60 and 70 have no minimum number. This is because the population estimates indicate a population below 30% of the pre-cull population.
In 2024, culling will begin in Area 73 and continue in Area 54 within the Low Risk Area. As explained in the December 2017 consultation document and the government’s subsequent response, minimum and maximum numbers are of less utility in the Low Risk Area given the different aim of the cull. However, Areas 54 and 73 are included in this paper for completeness. Area 32 – Cumbria has now moved to badger vaccination across the whole area. Further details on the areas and the evidence supporting a cull there, is set out in Annexes B and C.
For the purposes of determining the amount of vaccination required in 2023 to make a vaccination site in an Edge Area county eligible for a no-cull zone in 2024 inside areas beginning Supplementary Badger Culling, sites should meet the following criteria.
a. For sites with an area of 2.25km2 or larger there should be at least 2.7 badgers vaccinated per km2. The 2.7 per km2 minimum is based on the approach set out in the 2022 Advice to Natural England in setting the number of badgers that should be removed from a cull area in its first year. This is to ensure vaccination coverage is equivalent to the required cull level.
b. For sites smaller than 2.25km2 the number should be at least 6 badgers which is equivalent to the number needed for a 2.25km2 site to vaccinate 2.7per km2. This is to ensure that small sites are awarded a no-cull zone only if they have vaccinated a sufficient number of badgers to warrant preventing a cull on adjacent land.
Section C: Conclusions
As badger culling continues, we have learnt that there is uncertainty in estimating badger populations, and therefore in defining minimum numbers in subsequent years we needed to avoid false levels of confidence. As with previous years, we need to consider two realistic scenarios:
a. that during the cull, there is accumulating evidence that the number of badgers in the cull area is low, and that the number of badgers removed, despite a high level of contractor effort sustained across the whole cull area, is towards the lower end of our estimates. In this scenario, if the minimum and maximum numbers were set too high, Natural England would need to consider adjusting the numbers down to bring them in line with the actual circumstances being observed in the cull, so as to manage the risk of too many badgers being removed; OR
b. that during the cull, there is accumulating evidence that the number of badgers is higher than the minimum and maximum numbers suggest, either because the cull company quickly exceeds the minimum number, or because feedback from observations suggests there is a higher level of activity observed than expected. In these circumstances, Natural England would need to consider the need to compel the cull company to continue the cull by revising the minimum and maximum numbers upwards to ensure that the optimum disease benefits can be secured.
Daily data collected through the course of the cull about the level of effort being applied across the cull area, and locations of badgers removed, will enable Natural England to build an assessment of progress towards the cull total. This will allow Natural England to assess whether the estimated population was a reasonable reflection of the true population.
If the evidence suggests that there are more badgers than the estimates indicated (for example, because the number of badgers killed per unit effort is relatively high), Natural England will have the ability to revise the number upwards at an appropriate point, to ensure that the cull company is required to carry on the cull in order to achieve effective disease control.
Conversely, if the estimates are too high there will be a risk of removing too many badgers. In these circumstances, Natural England could, on the basis of careful consideration of the evidence and provided that the level of effort applied by the cull company has been sufficient, adjust the maximum number downwards at an appropriate point.
Annex A: Minimum and maximum numbers
Table 1: Minimum and maximum numbers for cull areas undergoing Supplementary Badger Culling.
| Area | Minimum number | Maximum number |
|---|---|---|
| Area 4 - Cornwall | 131 | 380 |
| Area 5 - Cornwall | 152 | 461 |
| Area 6 - Devon | 294 | 1173 |
| Area 7 - Devon | 145 | 455 |
| Area 8 - Dorset | 475 | 1685 |
| Area 9 - Gloucestershire | 219 | 1118 |
| Area 33 - Avon | 74 | 707 |
| Area 34 - Cheshire | 117 | 1124 |
| Area 35 - Cornwall | 263 | 1897 |
| Area 36 - Staffordshire | 100 | 648 |
| Area 37 - Devon | 193 | 985 |
| Area 38 - Devon | 173 | 1316 |
| Area 39 - Dorset | 51 | 484 |
| Area 40 - Herefordshire | 281 | 1253 |
| Area 41 - Staffordshire | 351 | 809 |
| Area 42 - Wiltshire | 19 | 2550 |
| Area 43 - Wiltshire | 64 | 1005 |
| Area 45 - Derbyshire | 425 | 1675 |
| Area 46 - Gloucestershire | 54 | 284 |
| Area 47 - Herefordshire | 284 | 1236 |
| Area 48 - Leicestershire | 82 | 432 |
| Area 49 - Oxfordshire | 128 | 621 |
| Area 50 - Shropshire | 256 | 2382 |
| Area 51 - Somerset | 56 | 1746 |
| Area 52 - Warwickshire | 200 | 1044 |
| Area 53 - Wiltshire | 64 | 329 |
Table 2: Minimum and maximum numbers for cull areas in their second, third and fourth years of badger control and Low Risk Area culls.
| Area | Minimum number | Maximum number |
|---|---|---|
| Area 54 - Lincolnshire | Not applicable | Not applicable |
| Area 55 - Shropshire | 0 | 92 |
| Area 56 - Hampshire | 152 | 521 |
| Area 57 - Berkshire | 70 | 215 |
| Area 58 - Staffordshire | 0 | 142 |
| Area 59 - Worcestershire | 0 | 218 |
| Area 60 - Shropshire | 0 | 640 |
| Area 61 - Oxfordshire | 131 | 467 |
| Area 62 - Buckinghamshire | 1316 | 1744 |
| Area 63 - Cornwall | 516 | 729 |
| Area 64 - Cornwall | 231 | 381 |
| Area 65 - Derbyshire | 380 | 779 |
| Area 66 - Devon | 294 | 433 |
| Area 67 - Hampshire | 199 | 450 |
| Area 68 - Northamptonshire | 431 | 1218 |
| Area 69 - Oxfordshire | 280 | 459 |
| Area 70 - Somerset | 0 | 49 |
| Area 71 - Warwickshire | 199 | 568 |
| Area 72 - Warwickshire | 566 | 1396 |
| Area 73 - Cumbria | Not applicable | Not applicable |
Annex B: Summary of Area 54 – Lincolnshire
Background
A hotspot area was established in June 2018 following the disclosure of M. bovis in a cattle herd in southwest Lincolnshire in the LRA of England, near the border with northeast Leicestershire in December 2017 (Hotspot 23; HS23). Infection is thought to have originally been introduced to the hotspot via cattle movements from the traditional homerange of this clade (Staffordshire, Shropshire, Cheshire or Derbyshire).
Collection and post-mortem examination (PME) of ‘found dead’ badgers and deer is ongoing in the area. There have been three positive badgers, two in the LRA and one in the Edge Area portion of the hotspot, all identified in 2020.
Whole Genome Sequencing (WGS), carried out on all cattle and badger isolates, shows that they are part of clade B3-11 and indicates that they are part of a distinct local cluster.
Assessing the options
In 2018, a simulation model was used to predict the potential epidemic length in badgers in Hotspot 21 (Cumbria) as there was little information on the level of infection in badgers. Culling was found to be the intervention most likely to result in the removal of infection from the badger population within an acceptable timescale. Whole Genome Sequencing in HS23 suggested through greater variation within the sequences found, that the initial level of badger infection may be greater than observed in Cumbria, as in there is more variation in sequences and less of a direct relationship to the local cattle cases, indicating that it may have been in the area for a longer period. PME results from the first year of operations confirmed this hypothesis.
Alongside this, APHA experts have now considered a further three years of results from PME of culled badgers (2021, 2022 and 2023) and the location of cattle breakdowns.
A total of 89 carcases from 2023 operations underwent PME, of which 4 were positive for Mycobacterium bovis (4.5% [95%CI 0.19, 8.8]). WGS was carried out and all isolates were clade B3-11. There has been an apparent prevalence reduction in the culled badgers across the four years of culling operations (24.5% in 2020, 10.3% in 2021, 7.5% in 2022 and 4.5% in 2023). As infected carcases were mostly central and there is some degree of distinct clustering, it is likely that badgers were originally infected multiple times from cattle.
The CVO has considered the issue and her advice is that as infection remains spread across the area and there has not yet been two years without infection, it is most appropriate to continue with badger culling to reach the overall aim of eradication.
Culled badgers will continue to be tested and the results of this, alongside the ongoing intensive surveillance of cattle, will inform future disease control measures in badgers and cattle in this area.
Annex C: Summary of Area 73 – Cumbria
Background
A hotspot area was established in January 2023 in response to the increase in Officially TB Free status Withdrawn (OTFW) breakdowns in the area over the previous years (Hotspot 29, HS29). Enhanced TB surveillance measures have been implemented in cattle and wildlife across the whole hotspot area. This includes an increase in cattle surveillance to six-monthly whole herd testing and the ongoing collection of ‘found dead’ badger and wild deer carcases. The WGS clade of M. bovis associated with HS29 is B3:11, predominantly found in Cheshire, Derbyshire, Staffordshire, and northeast Shropshire.
We previously reported in April 2024 that M. bovis had been isolated from one badger carcase in late 2023 and was genetically related to the local cattle cases. As an update, five further carcases have been identified as being infected with TB, bringing the total to six.
Assessing the options
As mentioned in Annex B, modelling was carried out for HS21 to predict the potential epidemic length in badgers as there was little information on the level of infection in badgers. Alongside this, the apparent prevalence reduction observed within badger carcases removed from other LRA badger control operations (Table 3) and results from cattle surveillance in the area were evaluated by APHA experts.
Table 3: Apparent prevalence of TB within badger carcases removed during cull operations within the Low Risk Area
| Operational year | Area 32-Cumbria (Hotspot 21) | Area 54-Lincolnshire (Hotspot 23) |
|---|---|---|
| 1 | 11.1% [95%CI 7.9, 14.3] | 24.5% [95%CI 17.4, 31.6] |
| 2 | 1% [95%CI 0.0, 2.04] | 10.3% [95%CI 5.5, 15.1] |
| 3 | 0% | 7.5% [95%CI 1.7, 13.3] |
| 4 | 0% | 4.5% [95%CI 0.19, 8.8] |
The CVO has considered the issue, noting the rapid increase in the number of infected badgers identified since April this year and the increasing cattle incidence. She advised that vaccination is unlikely to eradicate disease in this hotspot within an acceptable timeframe, so recommends that a licensed cull of badgers should be implemented as soon as it can be done effectively to reduce the risk of infection becoming established in the area.
Badgers removed during cull operations will undergo PME and the results of this, alongside the ongoing intensive surveillance of cattle, will inform future disease control measures in badgers and cattle in this area.