By Richard Black
Environment Correspondent, BBC News website
British government policies during the last 20 years may have contributed to the spread of TB in cattle.
Policy has been to cull badgers in areas near a TB outbreak; but new research says this spreads the disease because remaining badgers roam further.
It suggests that to be effective, culls must be widespread and thorough.
The government is due to announce a new policy on Thursday, with farmers' groups urging systematic culls and animal welfare groups arguing against.
The government is giving no clue about its intentions, but opposition MPs believe an extension of culling will be involved.
"My impression is that the government has been moving almost ineluctably to the inevitable conclusion that regrettably we must bear down on both cattle and wildlife," said Geoffrey Cox, Conservative MP for Torridge and West Devon.
"We do need an announcement now," he told the BBC News website. "We simply can't delay any longer."
Bovine TB has been spreading inexorably across Britain in recent decades, with incidence rising at about 18% per year.
The annual cost is estimated at £60m, which the National Farmers' Union (NFU) says could rise to £145m within five years.
Liberal Democrat Rural Affairs spokesperson Colin Breed MP also called for a decisive resolution, which he said should incorporate three elements:
"If this situation is not tackled in an urgent and positive way," he said, "we will inevitably see a continuing spread of the disease and continuing misery in the farming industry."
- an immediate and focused programme of badger control in hot spot areas
- the introduction of pre- and post- movement testing of cattle
- immediate and increased government support for the development of a vaccine.
Historically, many farmers have blamed badgers for spreading the bovine TB bacterium, and in 1986 the government introduced a strategy of culling badgers around infected farms.
A decade later, a committee chaired by Professor John Krebs began a policy review which concluded that a proper scientific assessment was needed.
Hence the establishment of the Randomised Badger Culling Trial, also known by its acronym RBCT or "the Krebs trial".
THE KREBS TRIAL
30 areas of the country, each 100 square km
10 culled proactively, 10 reactively, 10 not culled
Badgers culled through being caught in cage and then shot
Incidence of bovine TB measured on farms inside and outside study areas
Reactive culling suspended in 2003 after significant rise in infection
Trial cost £7m per year
It has already shown that the established approach of "reactive culling" near outbreak farms increased the incidence of bovine TB by 25%; whereas "proactive culling", aiming to kill all badgers in the area, brought the rate down by 19%.
A new scientific paper published in the journal Nature looked at farms just outside the proactively culled areas.
"What we demonstrate is a 19% reduction inside culled areas, but an increase of 29% in surrounding areas," said Professor Christl Donnelly from Imperial College London.
"From that we demonstrate that a single policy could simultaneously benefit some herds and be worse for others," she told the BBC News website.
The other scientific paper, from the Journal of Applied Ecology, attempted to find a reason why culling has these apparently contradictory effects.
According to study leader Rosie Woodroffe from the University of California at Davis, the key is that badgers expand their ranges when adjacent setts are culled.
"Everywhere where there is an impact on badger density there is also an impact on ranging," she told the BBC News website, "with animals travelling much more widely - not only in culled area but in adjoining areas.
"In reactively culled areas and around the borders of proactively culled areas you end up with not many fewer badgers, but with them travelling much further.
"I believe this can account for the findings in the Krebs trial."
Professors Woodroffe and Donnelly are both members of the Independent Scientific Group on Cattle TB, the government's advisory panel.
Britain and Ireland are the two countries hardest hit by bovine TB.
Habitat is undoubtedly a major reason; but Rosie Woodroffe believes the reactive culling policy may be another.
"It could have contributed to the spread of bovine TB," she said.
"The strategy was never formally tested so we can't know; but it's certainly plausible it would have made things worse."
Now farming minister Ben Bradshaw is poised to announce a change of policy which is almost certain, whatever choices he makes, to bring opprobrium from one side or other of a highly charged debate.
Snaring badgers is more effective but less humane
"Badgers are not the main source of TB in cattle," said Colin Booty, senior scientific officer of the RSPCA, which is resolutely opposed to culling.
"The trial results show that killing large numbers of badgers - most of which are disease-free - may even make the disease situation in cattle worse. Such a policy would clearly not be sustainable."
In the opposite corner is the National Farmers' Union, whose vice-president Meurig Raymond told the BBC News website: "A proactive cull can have a big impact.
"It would have to be done thoroughly, with well-defined boundaries."
Mr Raymond did acknowledge that farmers will have to accept stricter regimens of TB testing and restrictions on cattle movements if the disease is going to be controlled or eradicated.
Research published in May showed cattle movements to be the single biggest factor in TB spread.
The message from the two new scientific papers - which were both funded by Defra - is that if culling is to be effective, it has to be done over large areas and done thoroughly.
During the Krebs trial, some landowners refused to allow Defra staff access for catching and killing badgers.
A policy of enforcing access might be too draconian for government to contemplate.
Catching badgers with snares rather than cages is considered more effective, but also less humane.
The cost of a culling programme is a further issue.
Christl Donnelly views the choice before the government as extremely difficult.
"They have to decide on either very widespread culls over really expansive areas - but still some farmers would be upset to find themselves on the edge - or decide not to cull on the basis that on reasonable scales it's not going to be effective," she said.
"If I were in Ben Bradshaw's shoes, I honestly don't know; there is nothing I could choose that would make everyone happy."