New research virtually eliminates the likelihood of mad cow disease being transmitted from one generation of cattle to the next, a senior British government adviser on the disease has reported.
Professor John Wilesmith of the Veterinary Laboratories Agency said he was convinced animals could contract the deadly disease, also known as bovine spongiform encephalopathy (BSE), only by eating feed contaminated with meat and bone meal (MBM).
He suggested that continuing cases of the disease were due to contaminated feed, possible due to MBM residues in the holds of ships - a suggestion angrily dismissed by British feed manufacturers.
MBM is banned in the European Union because scientists believe it is the main agent spreading the virus, which has hit cattle herds in Britain, France, other European countries and Japan.
"I think the concern at the moment that we have is cross-contamination of feedstuffs which have been imported into Britain, and so there is still a possibility that one could get cross-contamination in the holds of ships," Wilesmith told BBC radio.
Wilesmith's experiments took embryos produced by BSE-infected cows and bulls and put them in the wombs of surrogate mothers. None of the calves or the surrogate mothers contracted the disease.
The UK Grain and Feed Trade Association blasted Wilesmith's remarks as "damaging conjecture."
"Imported vegetable proteins are shipped to the EU in vast tonnages in ocean-going vessels from exporting countries which have not had BSE and these vessels would not used for MBM," GAFTA said in a statement.
"The common practice in shipping feed materials is for all ships' holds to be cleaned and inspected by independent cargo surveyors/superintendents prior to the loading of cargo. It is therefore irresponsible of the Professor to make such a claim devoid of scientific evidence," it added.
Tim Miles, the chief veterinary surgeon at Britain's Meat and Livestock Commission, said that while the research left the cattle feed industry with a problem on how to screen imported feedstuffs, it was "very good news" for UK exports of embryos.
"We've got a complete ban in place on the export of live animals and embryos, so this research that shows there isn't any maternal transmission through this route means that we can press the case to get our embryos exported again," he said.
"We have put in place strict controls in the UK but we are at the mercy of any cross-contamination of our vegetable raw materials that might take place before we receive them," he said.
Britain first uncovered BSE in its national herd in 1986 and a decade later linked the disease to its deadly human equivalent, variant Creutzfeldt-Jakob disease, which has killed more than 100 people.