London

A strategy to control tuberculosis (TB) in cattle by killing thousands of badgers a year seems to do more harm than good, according to the initial results of a nationwide study in Britain.

Badgers carry the bacterium that causes TB in cows, and are thought to be an important reservoir for the disease. In an attempt to control bovine TB, the British government has overseen the culling of more than 20,000 badgers since 1975 in areas where herds are found to be infected — a strategy known as 'reactive culling'. This policy was put on hold in 1998 so that a study could assess the effectiveness of the method.

That study, led by John Bourne, a retired veterinarian formerly at the University of Reading, compared reactive culling with two other methods: no culling and 'proactive culling', in which badger numbers are reduced across entire trial areas regardless of the incidence of TB. The study involved 30 regions of England, each around 100 km2 in size, and was planned to run until 2005.

But Bourne's team decided last month to notify the government of the trial's initial results, as the number of infected herds in reactive-culling areas is now 27% higher than in regions without culls. The study does not reveal the cause of the increase, but researchers think that the culling may have prompted badgers to move between territories, increasing the spread of the disease. More results are required before they can judge whether the proactive strategy is more, or less, effective.

Ben Bradshaw, Britain's minister for nature conservation and fisheries, announced on 4 November that reactive culling will no longer be used in the trial. The results are disappointing for some, says Bradshaw, as reactive culling resulted in the death of fewer badgers than the proactive culling used in the trial. If effective, it could have been a compromise between farmers, who want to protect their cattle, and animal-welfare groups who oppose culling. “The reactive option would have been one of the most attractive policies for many people,” he says.

Stephen Harris, an expert on TB and badgers at the University of Bristol, notes that proactive culling can be altered to have a lesser effect on badger populations and the environment. But in the end, he notes, “the only long term solution to the problem is to develop a cattle vaccine”.