Korean researchers claim they have cloned four calves that will remain BSE free.

Professor Hwang Woo-sok from Seoul National University says his team has developed four cloned cows that are genetically modified to resist bovine spongiform encephalopathy (BSE), or mad cow disease. The cows have "antibodies specifically targeted against abnormal prions" that cause mad cow disease, said the professor.

Working with Japanese scientists early next year the Koreans now hope to use the technology to commercially produce BSE-free beef.

Hwang's team detected the BSE-resistant genes in the calves after inserting the prion-variation proteins into cells to prevent infestation. Hwang has now applied for an international patent on the genes.