The badger cull: an ‘evidence to policy’ perspective

Lots has already been written about the badger cull. There’s no dearth of emotive responses to it online. If you’ve visited my blog before, you’ll probably have picked up that I love wildlife. What you may not know is that, in my day job, I work on randomised controlled trials. More specifically, I work on translating the evidence we get from trials into policy and practice. So I’m trying to write this post with my ‘evidence to policy’ hat on.

Randomised controlled trials are the most reliable way of finding out if an intervention works. This short film explains why randomised controlled trials are important.

Outside of medicine, it’s rare for proper randomised controlled trials to be conducted to test if an intervention works. So the fact that a trial was conducted to test whether badger culling reduces bovine TB is a big deal. It means we have high quality evidence about the efficacy of badger culling.

So what did the Randomised Badger Cull Trial (RBCT) find?
The trial found that after 4 years of culling, bovine TB in cattle was reduced by 23% in the cull areas, but increased by 25% on the land less than 2km from the cull zone. It also found that localised reactive culls (where badgers are culled only after an outbreak of bovine TB) actually increased bovine TB in cattle.

Does this mean the current badger cull will help reduce bovine TB?
While it might initially seem that the evidence from the trial supports the current cull, it’s actually much more complicated. When working out whether the results are generalisable, (will apply in a different setting to the original research) we need to consider whether the intervention being used now is the same as that used in the trial.

In the RBCT badgers were culled by being trapped in cages then shot. This method is expensive, but it reduces the chances of badgers being missed, or being wounded and then escaping. The current cull is looking at free shooting, which hasn’t been trialled, and might not be so effective at killing badgers.

The proportion of badgers that are culled within an area is also important. In the trial, 70% of badgers in cull areas were killed. If the proportion killed is lower, it doesn’t simply mean there will be less reduction in bovine TB. This is because culling causes badgers to scatter further afield than they would otherwise (this is called perturbation), which, if they are infected with TB may actually result in increased transmission to cattle (as was found in the reactive cull areas, and those around the cull zone).

That’s why the pilot culls are important: we need to know whether free shooting is effective at killing enough badgers to make it likely that there may be a reduction in TB in cattle. Both pilot sites (Somerset and Gloucestershire) have been unable to kill the required proportion of badgers, and extensions to the cull periods have been applied for. The pilots have proven that free shooting cannot kill enough badgers quickly enough. This raises the risk that the culls may actually increase perturbation and therefore bovine TB.

What else needs to be considered when thinking about translating trial evidence into policy?

Cost-effectiveness RBCT found it wasn’t cost-effective. That’s why in the current cull they decided to go for free shooting rather than the more expensive trap and shoot used in the trial. The calculations were that it might be cost effective with this cheaper method. However, with the costs of policing the pilot estimated to run into millions, this now lookes unlikely. This is exacerbated by the apparent failure of free shooting to kill enough badgers. Failing to reach the target proportion of badgers culled increases the risk of the cull causing perturbance, which could increase bovine TB. To tackle this, there are reports that hundreds of cages have been brought in. This will increase the costs of the cull, and may well mean any benefits are outweighed by the monetary costs.

Feasibility: as well as considering whether an intervention is effective and cost-effective, policymakers need to consider whether it is feasible to implement it at the required scale and quality. The necessity of extending the length of the pilot culls would perhaps indicate that it is less feasible than anticipated.

Acceptability: clearly, given the keeness of the NFU to introduce badger culls, the intervention is acceptable to many farmers. It is equally clear that the measure is unacceptable to many in the general public, as evidenced by the number of signatures on petitions against the cull, and active protests around the country. It doesn’t look like a compromise is likely to be possible.

Need: bovine TB is a major problem, costing the UK £90m last year. Farmers and DEFRA argue that this means something must be done. However, it doesn’t make sense to argue that because something must be done we must do something that is likely to be ineffective (and probably harmful to the cattle who we are aiming to protect), and where the monetary benefits are outweighed by the monetary costs. We need to find ways to tackle bovine TB, but that doesn’t mean we should ignore the evidence on the likelihood of effectiveness and costs of any strategy.

Risk: a first principle of medical interventions is ‘first, do no harm’. The scientists who carried out the RBCT have come out strongly against the cull, saying it is not supported by the evidence, and is more likely to do harm to cattle than good.
Wiping out large numbers of badgers is likely to have effects on other animal species as well. We have to be careful when messing with the natural foodchain, as changes in the numbers of one species affect many other species. Reduced competition from badgers may well lead to an increase in other species, such as foxes, who aren’t too popular with many farmers either.

Ethics: badgers are protected by law. They are living creatures. One of the aims of the pilot cull was to assess the humaneness of free shooting as a method of killing badgers. It has now been admitted that it is unlikely to be able to tell us this. There is even talk of gassing of badgers in their sets, despite this having been outlawed 3 decades ago for being inhumane.

If we, as a society, are consciously going to wipe out large numbers of any of our native species, we need to be very sure it will have the effect we want. I believe the current evidence does not stack up. The cull is unlikely to significantly lower incidence of bovine TB, may actually increase it, and will cost more than the benefits are worth. We need to tackle bovine TB, but this is not the way.


8 thoughts on “The badger cull: an ‘evidence to policy’ perspective”

  1. Well done on preparing a balanced and informed blog.

    There are some things that trouble me, but I have not read the original research or the design of these culls. For example, it does not appear that the pre-cull bager populations are well established. Further, do the trials have the statistical rigour to distinguish between normal fluctuations in TB levels and the differences caused by the cull? Has the research adequately considered the dynamic effects – what happens as badger populations recover? Has a rigours economic impact assessment been undertaken that evaluates the impact on the dairy industry with the cost if the cull, associated research and policing and the cost of alternative abatement methods (which could be high if widespread prophylactic antibiotics are involved)? It is not clear to me that the proponents have really done their homework and if these trial culls will provide the certainty that is needed.

    1. You’re right, there does seem to be major uncertainty in the number of badgers in the two pilot cull zones. This BBC news article looks at some of the issues . Without a reliable estimate of the number of badgers in the population, it’s very hard to work out how many badgers need to be culled in order for the cull to be effective at reducing TB. Any illegal killing of badgers risks increasing perturbance and therefore cases of bovine TB in cattle.

      I suspect that any economic assessment carried out before the pilot culls began is now very out of date, considering the ineffectiveness of free shooting to kill enough badgers, and the need to extend the cull in both areas (to more than double the original planned length). I wouldn’t be surprised if the cost of policing has been higher than anticipated as well.

      Re. what happens as badger populations recover, the RBCT had a decent length of follow-up (10 years from the start of the cull, which lasted for four years), so we can be fairly confident about what would happen if the intervention was the same as that used in the RBCT. As that’s not the case, we’re really in unknown territory…

      One of the problems with bovine TB is there aren’t any brilliant alternative abatement measures. Infection control methods and limiting cattle movements can help, but are relatively expensive. There’s a trial going on for vaccinating badgers, so it will be interesting to see what that finds. The argument against that has been the cost, since you need to trap and inject each badger with the vaccine. Although since nobody’s going to protest about vaccinating badgers, by the time you take into account policing costs it may well look more attractive than culling, especially since they seem to have returned to trapping badgers for the cull. Vaccinating cattle is another option, but at the moment EU rules rule this option out effectively.

      The pilot culls were not really designed to test (properly, reliably) whether they actually decreased infections in cattle. They were meant to show whether free shooting was an effective cull mechanism, whether it’s humane, and whether it’s safe (not shooting passersby). It seems the only outcome it’s now going to be able to show is the latter…

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