Badger cull could cut TB by up to 30%
11:40am Wednesday 6th October 2010 in Badger cull in North Pembrokeshire
As a new consultation on plans to hold a badger cull in north Pembrokeshire begins, the Rural Affairs Minister is being urged to consider fresh data that reveals the reduction of bovine TB within the proposed cull zone could be more than three times higher than scientists had predicted.
According to a report by scientist Dr Nick Fenwick, the reduction in the incidence of bovine TB in the cull area could be as high as 30% during the five-year culling period, not the 9% the Assembly government had used to fight off a court challenge by the Badger Trust.
The 9% figure was based on updated results from the Randomised Badger Culling Trials (RBCT) in England, published in 2008, which considered a circular area of 125 sqkm with no significant boundaries such as the sea and mountains.
But a computer model designed by Dr Fenwick, which used the RBCT figures in an area that is the actual shape of north Pembrokeshire and covers 288 sqkm, shows that the reduction could in fact be closer to 29.79%. Dr Fenwick has simply included the boundaries of the sea, the River Teifi and the Preselis in his calculations.
His data and computer model were used to estimate the outcomes of culling in six areas the size of the north Pembrokeshire cull zone, each with different characteristics.
Central to his calculations was the varying effect of perturbation — movement of badgers resulting from disturbances created by a cull —depending on the distance from the cull area boundary. This negative effect would be lower in areas which were some distance from places where badgers could cross in and out of a culling area.
Even Dr Fenwick’s model showing the worst case scenario — a circular area with no boundaries — suggests there would be 14.49% fewer cases of TB over the five year culling period and 26.48% in the post culling period.
“All results show reductions in confirmed bovine TB incidences/reactors per bovine test as a result of badger culling, with percentage reductions at a maximum for culling areas with the most significant geographic boundaries,” says Dr Fenwick, agricultural policy director for the Farmers’ Union of Wales.
“For areas with such boundaries, the positive effects of culling could be expected to be more significant and last for longer than in areas without such boundaries, as was seen following the Thornbury trials, where culling led to a period of ten years with no confirmed bovine TB breakdowns”
The trial in Thornbury, Gloucestershire, in 1976 covered an area of 104 sqkm.
Clearance of virtually 100% of badgers in this trial area resulted in no cases of TB in cattle for a decade before re-colonisation by infected badgers.
Dr Fenwick believes the reductions achieved in England’s RBCT could be further improved in Wales beyond those predicted by his own results because the Assembly government would have tougher legislation in place relating to access and interference with culling.
“This would negate some of the problems experienced in England, resulting in a more efficient cull within a shorter period,” he says.
Despite his concern over the figure used by the Assembly government to argue its case for a cull, he says the decision to go ahead with a badger cull in an area that has one of the highest bovine TB incidences in northern Europe, and an estimated 1.86 infected badgers per square mile of open pasture, was one that was based firmly upon science.
“Given that it would take place in an area with significant geographic boundaries, thus reducing or eliminating perturbation, and alongside cattle restrictions that are even stricter than those which already exist, the results would be expected to be much better than those achieved by the English trials,” he says.
“There is no doubt that the decision was the right one, and Welsh Assembly Government staff and the minister deserve nothing but praise for their resolve. But it’s no good just using the figure for the worst case scenario, which includes non-existent cattle going down with TB in the Irish Sea. You have to also look at the results for best case scenarios and expect the real figure to be somewhere between the two.”