Tuesday, 4 June 2013

The science behind the badger cull

Before reading this blog post, please bear in mind that I am a marine ecologist not a badger ecologist! So this post reflects my personal investigation of the topic & my interpretation of the science behind the badger cull.

Most of us know what badgers look like though few of us will have ever seen them in the wild – sadly the only sight I’ve had of a badger is dead at the side of the road. They're difficult to see because these beautiful native mammals are nocturnal, so only emerge from their ‘setts’ (their underground burrows) at night to hunt and socialise.

European badger (c) ukwildlife
According to the recent state of nature report, badgers are one of the few species in the UK that have been increasing.  Based on a survey of badger setts carried out in the 90s, the number of badger social groups had increased over the previous decade by around 24% (each sett has a group of badgers that live together) – extrapolating this, the report estimated an increase in total numbers of badgers of around 77%. And current estimates suggest that there are around 350,000 badgers in the whole of the UK (a new population survey is currently in progress). One reason behind this increase may be the introduction of new laws to protect badgers introduced in the 1970s and subsequently (Badger Act 1973, Wildlife & Countryside Act 1982, Protection of Badgers act 1992).

But badgers also carry bovine TB (bTB) and are one of the causes of the transmission of bTB to cattle. Their increase is believed to be one of the factors in the recent increase of bTB in cattle. In 2012, over 28,000 cattle infected with bTB in England had to be slaughtered to the cost of £100m to the taxpayer, and unknown cost to the farmers themselves. The incidence of bTB in cattle has been increasing year on year to increasing concern to farmers.  But what can be done to reverse this trend? The Chief Scientific Advisor to DEFRA, Prof Ian Boyd, mentions 4 pillars of action in this video interview: (i) cattle testing & removal (i.e. killing) of infected animals; (ii) reducing cattle movement to avoid contact between infected & non-infected animals; (iii) vaccination; and (iv) wildlife control (i.e. culling).

As of the 1st June the government issued licences for trial culls of badgers in two areas to reduce the spread of bTB in cattle.  This cull will involve killing 5000 badgers in the two pilot zones in the southwest over a 6 week period, which is effectively 50-70 badgers killed per day. This will be repeated for 4 years. Sounds pretty grim!  The trial is to test that the cull can be done humanely, not that it is effective for reducing the spread of bTB.  So what science is the cull based on?

A large, near decade-long, scientific study was carried out 1998-2007 to scientifically examine the effectiveness of a cull – the Randomised Badger Culling Trial (report here if you have the energy to read the whole tome – it does make interesting reading, not that I've managed to read it all!). If you don’t want to read the whole tome, the BBC's Kate Humble’s video summary of the findings is a good overview. The study carried out trial culling of badgers in ten locations in the SW where bTB was on the increase in cattle. In 100 km2 patches (3 per area) badgers were either: (i) left undisturbed (as a control); (ii) killed only in and around farms with reported bTB; (iii) all animals trapped within the patch were killed (i.e. removal of 70% of the local population). The study showed that where badgers were only killed around farms with bTB, bTB incidence rose in cattle because the remaining badgers were ranging over larger areas increasing their contact with cattle (& with other badgers).  In the area where 70% of badgers were killed, although there was a reduction of bTB in cattle within the area (by 28%), outside the area there was an increase in bTB (of 9%) in adjacent farms.   So a cull would only work if culling was carried out at a massive scale, the cost of which was estimated to be higher than the current cost to farmers (& taxpayers) of dealing with infected cattle (not to mention the impact on badger populations).

The overall recommendation of the report was that ‘badger culling would make no meaningful contribution to TB control in cattle’. This view has been repeatedly endorsed by scientists such as Lord John Krebs who initially set up the trial.

I’m a scientist, and I like decisions to be based on good solid science – in my field there is often too little research carried out to have even a reasonable idea of effects of a particular action.  So to have a large study carried out over a long period of time looking at the effects of a cull on bTB in cattle, and for the study to conclude that culling is not scientifically justified… well it just doesn’t make sense in my mind!

What are the alternatives? The RBCT report suggests well-researched alternatives such as better bTB tests on cattle and further restrictions on cattle movement. Their report showed that a high level of bTB transmission occurs between cattle, so early diagnosis and eradication is essential to control the spread of the disease. And of course there is the vaccination route – either by vaccinating badgers or cattle (or both). This option has its own difficulties – catching and vaccinating every badger is challenging, and vaccinating cattle is currently prohibited by EU legislation because the vaccine interferes with the TB skin test (i.e. vaccinated cattle would test positive for bTB as would infected animals, the test can't distinguish between vaccinated & infected animals). I’m guessing that if the EU used the alternative TB test suggested in the RBCT report, this would get over this problem – so should we be lobbying at a European level? Though DEFRA say that a cattle TB vaccine is still a few years off.  One of the pro-cull arguments is that there is no science yet to show a positive effect of any badger vaccination program. This is true, though scientifically monitored trials of badger vaccination is currently being carried out in one area in the SW. Though this is only being carried out in one area rather than the 10 in the culling trial, and less than the original 6 planned (i.e. my interpretation is that the government are not really committed to the vaccination route).

Vaccination aside, the RBCT report suggested that even by carrying out the testing & cattle control measures they recommended could bring about a reduction in bTB incidence in cattle.  So I am hoping that the first two ‘pillars’ of action against bTB that Prof Ian Boyd mentions address these recommendations.

In conclusion? I tried to be unbiased in my investigation of the science behind the cull and really sympathised reading about the farmers who have had to kill so many of their infected cattle. But I am a scientist & the science seems pretty clear to me - researchers who have spent years/decades studying these animals, experts in this field of badger ecology and disease transmission, say that the cull is unlikely to have any meaningful impact on bTB in cattle. And putting aside the cute fluffy nature of badgers, I believe the science speaks for itself.

GREAT RESOURCE: the Wildlife Trust badger campaign with information on how to take action against the cull & really good background information.

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