Badger culling likely worse for bovine TB

There’s a world of difference between the European badger, Meles meles, and domestic cattle – on shoulder height and weight alone, a cow outsizes a badger by many multiples.

Both species are an immutable fixture of the British countryside – in imagination, a herd of Jersey milkers and a badger family go hand in hand.

So there’s no little irony in badgers being vectors for bovine tuberculosis (bTB).

Bovine TB is the most significant endemic livestock disease in the UK. The disease can be a huge burden on farmers and farm businesses, and badgers can pass the infection back to cattle, making it difficult to eradicate it.

Bovine TB can be treated but in the UK animals infected are more commonly killed, in part because of EU meat export regulations. In 2018, 5.8% of herds in the UK were affected by it.

UK conservationists, vets and farmers have been at loggerheads for many years about the best way to manage bTB.

Following random badger culling trials during 1998–2008, the UK Government announced a culling policy in 2011. The aim is to reduce badger populations by at least 70% across a cull zone that currently covers a substantial part of England’s southwest peninsula, which includes the counties of Somerset, Devon and Cornwall. 

Now, a study led by researchers at the Zoological Society of London (ZSL) and Imperial College London has found that culling drives badgers to roam further afield, which can sometimes exacerbate the transmission of bTB instead of reducing it.

Between 2013 and 2017, the researchers collected GPS-collar data from 67 badgers across 20 cattle farms, in areas with and without culling, in Cornwall.

The study – published in the Journal of Applied Ecology – reveals that badgers that survive a cull cover 61% more land each month than they had before the cull began. 

The researchers believe they explore new areas as individuals are removed from neighbouring groups and territories open up.

Badgers were also found to visit 45% more fields each month, and the odds of a badger visiting neighbouring territories each night increased 20-fold – potentially increasing the risk of TB transmission both to cattle and to other badgers.

These changes were witnessed as soon as culling began, meaning even badgers that were later killed may have first spread the infection over wider areas.

Researchers also learned that badgers spent on average 91 minutes less per night outside of their setts – dens – in culled areas. They believe this could be linked to reduced competition and increased food availability as badgers are removed from the population.

“Badgers spend a large proportion of the night foraging for food above-ground, and as culling reduces the size of the population, competition for food will also be reduced,” explains lead author Cally Ham.

“We believe this accounts for the reduced activity levels, as well as bold individuals becoming obvious targets for culling and being quickly removed from the population.”

Culling partly relies on shooting badgers that are moving around at night, and Ham says the fact that badgers were active for fewer hours per night could actually be undermining the effort to control badger numbers through culling.

ZSL’s Rosie Woodroffe believes a change in approach to managing bTB transmission is necessary.

“As badger-to-cattle transmission is likely to occur through contamination of their shared environment, and TB bacteria can remain viable for long periods of time in the environment, the effects of increases in ranging behaviour could create a source of infection for several months – long after the individual badger has been culled,” says Woodroffe.

“In contrast, studies have shown that vaccination prompts no changes in badgers’ ranging behaviour.”

A recent independent review advised the UK government to explore badger vaccination as an alternative to culling. The Irish government is already moving from culling to vaccination.