Absence of effects of widespread badger culling on tuberculosis in cattle

Abstract

Government policy in England aims for the elimination of bovine tuberculosis (bTB). This policy includes culling of European badger (Meles meles) to reduce cattle TB incidence. The rationale is based on the results of a field trial, the Randomised Badger Culling Trial (RBCT) 1998–2005, which reported a substantial decrease in bTB herd incidence where badger culling had been implemented, in comparison to untreated control areas. The results were reported in 2006 in the journal Nature. Recent analysis of proactive badger culling in England since 2013 has raised concerns that badger culling, based on RBCT methods, may not reduce bTB herd incidence. The present study re-examined data from the RBCT experiment using a range of statistical models. It concluded that most analytical options did not show any evidence to support an effect of badger culling on herd incidence of bTB ‘confirmed’ by visible lesions or bacterial culture post mortem. However, the statistical model selected and reported from the RBCT study was one of the few models that did show an effect. Various criteria suggest that this was not an optimal model compared to other analytical options then available. The most likely explanation is that the RBCT proactive cull analysis overfitted the data with a non standard method to control for exposure. This resulted in it having a poor predictive value. Fresh appraisals suggest that evidence from more suitable analysis of the original data show that badger culling does not bring about the reported effects. The RBCT found no evidence of an effect on ‘total’ (confirmed and unconfirmed) bTB herd incidence, which we have also found using the more suitable statistical models. The selective choice of use only of ‘confirmed’ incidence data, together with more recent (2013) published perception that RBCT data presented ‘a strong evidence base….with appropriate detailed statistical or other quantitative analysis’ should now be adjusted to conclude that this evidence base is weak or at least, equivocal. The results of the present report are consistent with findings that badger culling in England (2013–2019) shows no significant disease control benefit. The findings of this study help explain one form of driver to the reproducibility crisis, in this case with disease control management in an increasingly intensified livestock industry.