April 4, 2014

expert reaction to Princess Anne’s comments on gassing badgers

Princess Anne is reported to have told the BBC’s Countryfile programme that gassing badgers is “the most humane way” to control their numbers.

Dr Chris Cheeseman, former Head of Wildlife Diseases at the Central Science Laboratory (now the Animal Health and Veterinary Laboratories Agency), said:

“The constant focus on badger culling is a distraction from the central issue regarding bovine TB, i.e. the failure of the cattle TB testing regime to identify and remove infected cattle and prevent the onward spread of bovine TB.  Approximately one in five infected cattle are missed during routing skin testing using the SICCT test (single intradermal comparative cervical tuberculin test) and the movement of cattle from apparently TB free herds is a source of further cattle-to-cattle transmission.  The latest statistics from Wales have demonstrated how improvements to cattle testing have reduced cattle TB incidence by 48% in just five years, without any badger culling.

“The failure of the Government’s recent pilot culls was firmly predicted by experts.  Controlled shooting failed to achieve the prescribed efficiency target of 70% of the estimated badger population, with less than half this figure being achieved.  Shooting also failed on humane grounds with an unacceptably high proportion of badgers living longer than five minutes after being shot.  A common reaction to this outcome is to suggest an alternative means of culling and the gassing of badger setts is often mentioned.

“Badger setts were gassed with hydrogen cyanide (HCN) as part of an early TB control programme from 1975 to 1982.  After a review by Lord Zuckerman, who suggested that ways should be found of making the gassing of setts more efficient, work was commissioned with the Government’s Chemical Defence establishment at Porton Down.  What happened was totally unexpected.

“It was believed that HCN was humane in action, whereby animals either lapsed into unconsciousness when exposed to HCN and either died or recovered without ill effect from a sub-lethal dose.  Watching badgers exposed to HCN, retching and vomiting while uttering distress calls, is an experience I shall never forget.  Gassing was immediately halted as a control method and live trapping followed by shooting was adopted in its place.

“Apart from the need to establish whether any new gasses, such as carbon monoxide or carbon dioxide, are humane in action, it would be necessary to overcome the practical difficulties of gassing setts in inaccessible places, such as steep, thickly wooded banks, tin mine shafts or cliff edges.  There is also the problem of achieving lethal concentrations of gas in the blind ended tunnels of a sett – badgers often reopened setts gassed with HCN from the inside.  Then there is the problem of killing non-target species such as polecats, otters and the many protected small mammals that frequently occupy setts.

“Finally, it would be necessary to devise a strategy which would avoid the possibility of causing local extinction of badger populations, since this would contravene the Bern Convention and have unknown ecological impacts, and establish whether gassing caused any negative perturbation influences that might exacerbate the spread of TB in both badgers and cattle.”

Prof Rosie Woodroffe, Senior Research Fellow, Institute of Zoology, Zoological Society of London (ZSL), said:

“TB is a terrible problem for farmers and farming families, and it demands an effective solution. Unfortunately, as we know from the report on the pilot culls published yesterday, free shooting of badgers was both ineffective and inhumane. Cage trapping can be effective and humane when done properly but it’s extremely expensive. So, it’s tempting to think that it might be easier to kill badgers when they’re essentially a sitting target, underground in their setts.

“Unfortunately it’s not that straightforward. Gassing badgers was government policy in the 1970s, and reports of the time are full of frustration about how it just wasn’t very effective. Setts would be gassed, and then repeatedly opened up by the badgers. It seemed not to work well in Cornwall, “because of the granite”, it seemed not to work well in summer, “because of the dry soil”. The problem seemed to be that badger setts are built to hold warm air in and keep cold drafts out – so it was very difficult to achieve lethal concentrations of gas. And, sub-lethal concentrations of gas were inhumane. That’s why gassing was banned by ministers in 1982.

“In Britain, any TB control approach based on culling badgers is going to be dogged by the problem of perturbation, and that’s because culling works against the grain of badger ecology and behaviour. It’s much more promising to explore the possibilities for vaccination, which could potentially exploit the same aspects of badger biology to improve the effectiveness of TB control.”