Analysis of further data on the impacts on cattle TB incidence of repeated badger culling

Helen E. Jenkins1, Rosie Woodroffe2, Christl A. Donnelly1*

1 Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom
2 Institute of Zoology, London, United Kingdom

* E-mail: c.donnelly@imperial.ac.uk

Since publication of the paper “The duration of the effects of repeated widespread badger culling on cattle TB following the cessation of culling”, an additional six months of cattle testing data have become available. These allowed analyses to be updated.

In the time period from one year after the last proactive cull to 31 January 2010 (the post-trial period), the incidence of confirmed breakdowns in the proactive culling areas was 37.0% lower (95% CI: 25.3% to 46.8% lower) than in survey-only areas and in areas up to 2km outside proactive trial areas was 3.6% lower (95% CI: 29.0% lower to 31.0% higher) than outside survey-only areas.

Exploratory analyses stratified by 6-month periods (Table 1) suggested, unexpectedly, that the beneficial effects observed within trial areas in the first year post-trial, have reappeared in the last 6-month period analysed (37 to 42 months post-trial).

These latest results are consistent with a constant benefit of proactive culling continuing through this latest period. However, the effects observed outside trial areas are consistent with no ongoing effects of proactive culling in these areas.

There is no clear explanation for the unexpected pattern observed within trial areas based on these latest data. (We examined parish test intervals and they are very similar in and around proactive and survey-only trial areas.) Continued monitoring is necessary to quantify any further temporal changes in the effects.


Table 1 Estimated effects of proactive culling on the incidence of confirmed cattle TB breakdowns inside trial areas. Analyses adjust for triplet, baseline herds, and historic TB incidence (over three years). Results are split by 6-month period post-trial and include breakdowns from the initial cull to 31 January 2010.

Time period Estimate (95% CI) p-value
(post-trial)
----------------------------------------------------------------
Months 1-6 -52.4% (-71.2%, -21.1%) 0.004
Months 7-12 -40.7% (-63.3%, -4.1%) 0.033
Months 13-18 -49.2% (-67.4%, -20.8%) 0.003
Months 19-24 -27.4% (-51.7%, 9.0%) 0.12
Months 25-30 -31.8% (-56.8%, 7.7%) 0.10
Months 31-36 -7.6% (-41.1%, 45.1%) 0.73
Months 37-42* -43.5% (-65.2%, -8.2%) 0.021

[* This time period had 4.3 triplet-years of data as of 31 January 2010; other time periods had the full 5.0 triplet-years.]


Funding: The authors gratefully acknowledge the support of the United Kingdom Department of Environment, Food and Rural Affairs (Defra; http://www.defra.gov.uk/i...) for this work. CAD thanks the United Kingdom Medical Research Council (http://www.mrc.ac.uk/inde...) for Centre funding. HEJ thanks the Medical Research Council for a studentship.