December 16, 2016

expert reaction to Defra statement on badger culling figures

Defra announces latest badger culling figures.

Prof. Rosie Woodroffe, Senior Research Fellow, Institute of Zoology, Zoological Society of London, said:

“This cull killed 10,886 badgers in just 6 weeks – almost as many as the Randomised Badger Culling Trial took in the course of a 10-year study.

“The Chief Veterinary Officer concludes that “The outcome of this year’s culls indicates that industry-led culling can deliver the level of effectiveness required to be confident of achieving disease control benefits”

“However, a close reading of the evidence suggests that there is no basis for drawing any conclusions about the effectiveness of culling.

“Defra measures the short-term effectiveness of culling not in terms of the reduction in cattle TB, but in terms of the reduction in the badger population. This is because (i) it takes several years for culling to generate reductions in cattle TB; and (ii) reductions in badger density of <<70% have been shown to increase cattle TB rather than reducing it. Hence, Defra’s policy aims to reduce badger density by “at least 70%”.

“Unfortunately, there is no way to judge the % reduction in badger density achieved by these culls, and hence no way to determine whether they can be expected to reduce cattle TB, or increase it. Here’s why.

“In each culling area, a cull company was given a minimum and maximum number of badgers they were required to kill – this was based on estimates of average badger densities, not on any surveys in the cull areas themselves.

“Perhaps unsurprisingly, the numbers of badgers actually present in each area turned out to be highly variable. The government responded to this by revising the culling targets in all seven new areas. Where few badgers were killed in the first month of culling, they lowered the targets; where alot were killed, they raised them. This means that there is really no way to tell what reduction in badger numbers was achieved by these culls. For example, an incompetent culling company that killed very few badgers would be interpreted as a low badger density and prompt a reduced target.

“The Chief Veterinary Officers’s conclusion that “The outcome of this year’s culls indicates that industry-led culling can deliver the level of effectiveness required to be confident of achieving disease control benefits” is not based on reliable evidence.

“It is important to be aware that data available so far have not yielded any evidence of a reduction in cattle TB in the areas culled to date. This is not surprising, because so far data have been analysed only from the first two years of culling, whereas benefits took up to four years to emerge in the Randomised Badger Culling Trial. However, it does highlight that Defra has embarked upon a widespread rollout of farmer-led badger culling in the absence of firm evidence that this approach can reduce cattle TB.

“The government is consulting on plans to continue culling after these initial 4-year culls, as the first 2 areas have completed their 4 year licences. This is a big step away from the RBCT which saw the greatest reductions in cattle TB after culling was halted, potentially because perturbation of badger behaviour ended when culling ended, yet badger densities were low.

“These new licences would be for 5 years, with an option to apply again – that is, culling would be essentially open-ended.

“Worryingly, Defra has indicated that these subsequent culls would not require specified levels of landholder participation – that is, badger culling could become patchy. This is worrying because the RBCT showed that patchy culling increased cattle TB rather than reducing it.

“Overall, Defra appears to be proceeding with a widespread rollout of badger culling in the absence of convincing supporting evidence.”

* https://www.gov.uk/government/news/tb-strategy-ahead-of-schedule-as-england-set-to-apply-for-officially-tb-free-status-for-half-the-country

All our previous output on this subject can be seen at this weblink: http://www.sciencemediacentre.org/tag/bovine-tb/ 

Declared interests

Prof. Rosie Woodroffe: “In the past I have received financial and in-kind support from Defra.”