Setting the minimum and maximum numbers in badger cull areas in 2023: advice to Natural England
Published 7 September 2023
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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 2022, 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 is taking place in 2023.
- Section B covers the areas where culling began in 2020 to 2022.
- Section C covers concluding remarks affecting all of the areas (No new badger control licenses will be issued in 2023).
To ensure that the special status of the 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 continue in Area 54-Lincolnshire. Area 32-Cumbria continues to have vaccination across the whole area.
Section A: Areas 3 to 10, Areas 22 to 31 and Areas 33 to 43
In 2023, Areas 3 to 10 and Areas 22 to 31 will continue Supplementary Badger Control. Areas 33 to 43 inclusive will begin Supplementary Badger Control.
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.
Areas 11 to 21 inclusive have now ceased culling operations after completing the second and final year of their SBC licence in 2022
Section B: Areas 44 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. APHA surveyors carried out a Quality Assurance check in sample parcels across the whole of the cull areas in year two areas.
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 45, 47, 48, 55 and 58 have no minimum number, this is because the population estimates indicate a population below 30% of the pre-cull population.
In 2023, culling will continue in Area 54 in 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, Area 54-Lincolnshire is included in this paper for completeness. Area 32 has now moved to 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 2022 to make a vaccination site in an Edge Area county eligible for a no-cull zone in 2023 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 3: Dorset | 163 | 383 |
| 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 10: Herefordshire | 90 | 359 |
| Area 22: Cornwall | 448 | 1948 |
| Area 23: Devon | 146 | 1465 |
| Area 24: Devon | 114 | 421 |
| Area 25: Devon | 39 | 534 |
| Area 26: Devon | 55 | 569 |
| Area 27: Devon | 36 | 154 |
| Area 28: Devon | 36 | 302 |
| Area 29: Gloucestershire | 172 | 878 |
| Area 30: Somerset | 230 | 1795 |
| Area 31: Staffordshire | 373 | 2492 |
| Area 33: Avon | 74 | 707 |
| Area 34: Cheshire | 98 | 938 |
| 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 |
Table 2 Minimum and maximum numbers for cull areas in their second, third and fourth years of badger control.
| Area | Minimum number | Maximum number |
|---|---|---|
| Area 44: Avon | 89 | 1113 |
| Area 45: Derbyshire | 0 | 1066 |
| Area 46: Gloucestershire | 136 | 356 |
| Area 47: Herefordshire | 0 | 618 |
| Area 48: Leicestershire | 0 | 100 |
| Area 49: Oxfordshire | 230 | 723 |
| Area 50: Shropshire | 2494 | 4571 |
| Area 51: Somerset | 118 | 1736 |
| Area 52: Warwickshire | 98 | 941 |
| Area 53: Wiltshire | 96 | 347 |
| Area 54: Lincolnshire | Not applicable | Not applicable |
| Area 55: Shropshire | 0 | 46 |
| Area 56: Hampshire | 335 | 703 |
| Area 57: Berkshire | 356 | 501 |
| Area 58: Staffordshire | 0 | 253 |
| Area 59: Worcestershire | 131 | 351 |
| Area 60: Shropshire | 364 | 1036 |
| Area 61: Oxfordshire | 287 | 622 |
| Area 62: Buckinghamshire | 859 | 1405 |
| Area 63: Cornwall | 384 | 624 |
| Area 64: Cornwall | 106 | 256 |
| Area 65: Derbyshire | 376 | 810 |
| Area 66: Devon | 305 | 462 |
| Area 67: Hampshire | 286 | 537 |
| Area 68: Northamptonshire | 797 | 1658 |
| Area 69: Oxfordshire | 291 | 489 |
| Area 70: Somerset | 46 | 120 |
| Area 71: Warwickshire | 280 | 648 |
| Area 72: Warwickshire | 1136 | 1978 |
Annex B: Summary of Area 32-Cumbria
Background
A potential ‘hotspot’ area was declared in east Cumbria in the LRA of England during 2016 (Hotspot 21, HS21). This was due to the emergence of a cluster of breakdowns associated with Mycobacterium bovis genotype 17:z. This genotype had not previously been identified in Great Britain, and investigations concluded that this was most likely introduced by cattle imported from Northern Ireland.
From identification of the index case in November 2014 to 25 August 2023 there have been a total of 60 breakdowns in 50 holdings, and 53 breakdowns associated with HS21. There are currently three open breakdowns. Collection of ‘found dead’ badgers and deer is ongoing in the area (not all reported carcases are collected and submitted for PME. Read more about TB surveillance in wildlife. There have been three positive badgers, all of which were identified in 2017.
Assessing the options
In 2018, a simulation model was used to predict the potential epidemic length in badgers in HS21 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. In 2019, 2020 and 2021, the results from the surveillance carried out on culled badgers were considered by APHA epidemiologists and ecologists to make recommendations for intervention measures. Vaccination was carried out across the whole area in 2022.
The CVO has considered the results and her advice is that badger control, whether culling or vaccination, still should remain in place for a sixth year as we are making tangible progress towards eradication. The aim of badger control within the LRA is disease eradication.
There was no evidence of re-emerging infection within the badger population in Area 32. Therefore, vaccination continued across the whole 214km2 area. This year’s vaccination operations were carried out between May and July of 2023 with 169 badgers vaccinated. The total number of vaccine doses delivered since 2020 is 520 (Vaccination was delivered over 103km2 in 2020, 140km2 in 2021 and the whole 214km2 area in 2022 and 2023).
Based on the evidence to date from cattle and wildlife surveillance showing an improving disease picture, APHA have continued to reduce the cattle testing frequency from six monthly to annual. All cattle keepers are now eligible for annual testing. Cattle keepers must meet various risk-based criteria and will be assessed on a case-by-case basis.
‘Found dead’ badgers and deer 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 54 – Lincolnshire
Background
A potential ‘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). Due to its proximity to, and shared genotype with, a cluster of Officially TB Free status Withdrawn (OTFW) breakdowns in northeast Leicestershire, the hotspot is situated partially in the LRA and partially in the Edge Area.
From identification of the index case within December 2017 to 25 August 2023 there have been a total of 110 breakdowns across 100 holdings. There are currently eight open breakdowns. Collection 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 (encompassing the previous genotype 25:a and 25:b) and indicates that they are part of a distinct local cluster. Infection is thought to have originally been introduced to the Edge Area portion of the hotspot via cattle movements from the traditional homerange of this clade (Staffordshire, Shropshire, Cheshire or Derbyshire)
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. 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 (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 of time). PME results from the first year of operations confirmed the hypothesis that the level of infection in this area was higher than that in Area 32.
Alongside this, APHA experts have now considered a further two years of results from PME of culled badgers (2021 and 2022) alongside the location of cattle breakdowns.
A total of 80 carcases from 2022 operations underwent PME, of which 6 were positive for M. bovis (7.5%). WGS was carried out and all isolates were clade B3-11. There has been an apparent prevalence reduction in the culled badgers across the two years of culling operations (24.5% in 2020, 10.3% in 2021, 7.5% in 2022). 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.
Infected badgers from 2022 operations were disclosed on the eastern boundary of the cull area. APHA ecologists and epidemiologists have advised that the boundaries of the cull area should extend to the east to manage the risk that infection is located across a wider area than evidence currently shows.
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.