The badger cull – what we know and what we don’t know

Bovine tuberculosis (bTB) is an infectious disease of cattle (Bos primigenius) caused by the bacterium Mycobacterium bovis. You could follow my ‘tuberculosis’ tag.

Other animals can get bTB too. In Britain, some people think the native badger (Meles meles) is a reservoir of bTB, so badgers are being shot. In New Zealand (NZ), the non-native brushtail possum (Trichosurus vulpecula) was identified as a bTB reservoir, so possums were poisoned. I’ve compared bTB in NZ to bTB in Britain and Ireland.

The unnamed author of bovinetb.info tells us about bTB in NZ. At the end of that article, you can read part of a 2009 email from Paul Livingstone of the NZ Animal Health Board. Dr Livingstone said, ‘[Y]our main source of infection for cattle… is the badger,’ but he didn’t explain what evidence led him to that view. Here in Britain, that’s a controversial opinion.

A few days ago Patrick Worrall at one of our commercial television channels, Channel 4, summarised what we know and what we don’t know about badgers and bTB. It’s a good article, quite unbiased I think.

‘[T]he Independent Scientific Group (ISG) on Cattle TB, which spent nearly a decade carrying out experimental badger culls and collecting data, concluded that “badgers contribute significantly to the disease in cattle”.

‘ISG member Christl Donnelly has found “close positive relationships” between TB in cattle herds and badgers carrying the disease. Last year she estimated that around 50 per cent of bovine TB incidents recorded in the study could be attributed to infectious badgers.’

So shoot the blimmin badgers! So say many farmers.

But are badger populations rising? If so, are they spreading bTB?

Mr Worrall tells us that our Department of Environment Food and Rural Affairs (DEFRA) says that ‘an anecdotal rise in badger numbers “is not known for certain”.’ This is the kind of thing that Government Department should know. If DEFRA doesn’t know, I don’t think anybody knows.

Mr Worrall continues, ‘[O]utbreaks of bovine TB went up dramatically in 2001 and 2002, which some have interpreted as the effect of an influx of untested cattle arriving in the country as farmers restocked their herds after the foot and mouth epidemic. It may have nothing to do with badgers…

‘ISG’s big 10-year badger study concluded that badgers were probably partly to blame for TB in cattle, [but] stated unequivocally that: “Badger culling can make no meaningful contribution to cattle TB control in Britain…” if you trap or shoot badgers in a certain area, it pushes them into neighbouring areas (“perturbation”). So TB rates go down in a hot spot only to increase outside the culling zone. The ISG results suggest that four years of intensive culling could cut bovine TB by 12 to 16 per cent after nine years.’

Reducing bTB culls of cattle herds by 12-16% at best. Not very impressive, I think.

Anyway, says Mr Worrall, ‘If badgers really are the problem, keeping them out of farms may be the answer. Some dairy farmers have claimed to maintain completely TB-free herds for decades using “biosecurity” measures like badger-proofing cattle troughs.’

He finishes with a summary of how bTB is known to infect other wildlife including ‘foxes, stoats, shrews, polecats, mice, voles, squirrels and most species of deer… Watch out, Bambi.’

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