A world authority on foot-and-mouth and adviser to the Prime Minister yesterday questioned the slaughter of thousands of healthy animals as part of the Government's draconian culling policy. Alex Donaldson, head of the Institute for Animal Health's Laboratory at Pirbright in Surrey, said the policy of culling every animal on neighbouring or contiguous premises to an infected farm may have been "excessive".
Dr Donaldson, who is on the Cabinet Office committee of government advisers which proposed the culling policy, said the computer models used to justify the approach were oversimplified and may have given inaccurate forecasts.
He studied the probability of the virus spreading by the wind, one of the principle reasons for contiguous culling. His research showed the risks of airborne transmission were significant only when pigs were known to be infected. The chances of the virus spreading were far smaller when sheep and cattle were infected.
The study, published in this week's Veterinary Record, showed that airborne transmission from cattle and sheep strikes at no more than about 200 metres rather than the several kilometres assumed by the computer modellers. "The modellers did not define the mechanism of "local" spread, but assumed it would happen as a statistical probability," the study by Dr Donaldson and his colleagues said.
The scientists also criticised the computer modellers for failing to take into account the differences between sheep, cattle and pigs and assuming all species affected by foot-and-mouth behave in the same way when transmitting the virus.
"Given the very wide variation between different species in terms of the quantities of virus excreted, their susceptibility to infection, and the routes by which they are likely to be infected, the modelling of the spread of foot-and-mouth disease using an average species is an over-simplification, and in certain circumstances would have generated inaccurate forecasts."
Dr Donaldson said the low risk of foot-and-mouth being spread by the wind from one farm to another when pigs were not involved undermined the rationale for contiguous culling of many thousands of sheep and cattle. "I haven't seen that policy used before, at least not on a contiguous basis," Dr Donaldson told Radio 4's Today programme. "But I think one will need to make a judgement as to whether that was justifiable or over the top. I think there are some pointers which would suggest to me that it may have been excessive."
Dr Donaldson was asked whether enough was done to tackle the epidemic using a more conventional approach, such as targeted culling. "Had there been sufficient support for the more traditional approaches, one could speculate that those traditional approaches would have worked," he said. The contiguous culling policy has been largely responsible for the slaughter of 2.4 million animals, more than five times the number killed during the 1967 epidemic when the number of confirmed cases was smaller.
Professor David King, the government's chief scientific adviser, vigorously defended the culling operation, saying many more animals would have been slaughtered if contiguous culling had not been enforced so ruthlessly.
"If we look at the way the policy was implemented," he said, "it was implemented at the point when the outbreak was out of control and it worked."