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Monday, July 25, 2011

Liberal Democrat MP criticises English badger cull

The Liberal Democrat MP for Torbay, Adrian Sanders has come out strongly against the UK Government's plan to cull badgers as part of its anti-bovine TB strategy. Writing in a news release featured on his website, Adrian says:

“No one should underestimate the cruel impact of TB in cattle or in badgers, and its emotional and economic effects on farmers, but any response must be based on science and the Government has failed to take on the advice from research conducted by the Independent Scientific Group (ISG).

This found that “Given its high costs and low benefits we… conclude that badger culling is unlikely to contribute usefully to the control of cattle TB in Britain, and recommend that TB control efforts focus on measures other than badger culling.”

The ISG instead called for a more cattle focused approach to dealing with the spread of the disease which Adrian supports. The need for a cattle based approach is strengthened by estimates that badgers are only responsible for 30-40 percent of cattle TB. The reason for the spread and increase of the disease is instead more likely to be because of a relaxation of cattle testing, less regulation concerning slaughter and movement and an intensification of dairy farms.

Adrian said “I regret that the Government have reached this decision which I believe will not have the desired results of stopping the spread of TB, but instead will lead to the loss of life of badgers and potentially other innocent creatures, such as domestic cats, if as a leading farmer in Devon has suggested armed groups will work at night.

Adrian pledged to join others in persuading the Government to return to the Coalition Programme for Government policy that states no cull should take place unless the scientific evidence supports it.”

In fact there is evidence that farm cats may be susceptible to bTB, and may well infect cattle. It is not just badgers that pass on this disease, it will jump species randomly. It is for this reason that the most effective way to tackle this disease is through vaccination.

There was an interesting article by Ben Goldacre on the Guardian website last week in which he argues that the Government is extrapolating incorrectly from previous trials:

You'd have thought this culling should do some good, or at least no harm. In fact, the "reactive culling" was stopped after a few years when the rates of cattle TB infections in these areas turned out to be higher than areas with no culling, by about 20%.

One suggested explanation was "perturbation". Badgers live in small groups, with territorial boundaries; if you kill some, the groups are disrupted, and the animals wander further afield, spreading infections more widely. But the results from the "proactive culling" were more interesting. In the 100km2 culling zone, cattle TB infections fell by about a quarter. But in the 2km-wide "ring" around the proactive culling zone, the number of TB infections in cattle rose by about a quarter, perhaps, again, because of "perturbation".

A 2km ring becomes less important when the culling area is larger, and mathematical modelling suggests that after 150km2, the extra TB infections in the ring are outweighed by the benefits in the cull zone. At this size, you prevent 23 of the 187 expected herd outbreaks, and so save £600,000 ( outbreaks each cost £27,000). The cost, however, using the cage-trapping method used in the trial, is £2.14m. This is why people concluded it wasn't worth the effort.

Here is the second science bit. The government is now introducing a kind of farmer-led culling. This costs around £500,000 for the same size area, and so now a cull becomes cost-effective, by a hair. But we also end up several steps away from the scientific evidence. First, we're assuming that results from small cull zones scale up neatly into larger ones, and that killing can be done uniformly without local perturbation.

But more importantly, the trial loses what evidence nerds call "external validity": the ideal perfect intervention, used in the trial, is very different to the boring, cheap, real-world intervention that the trial is being used to justify.

Under the UK Government's current plans, the idea as I understand it is to licence individual farmers to cull on their own land. Unless there is 100% take-up then the outcome is inevitably going to be perturbation within the cull area and the spreading of bTB to previously unaffected areas.

I would suggest that such an approach is even more prone to judicial review than the inept approach taken by the One Wales Government.
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