BSE is passed on by an infectious protein particle called a prion. Neither a living organism nor a virus, it is a misshapen protein that can convert other proteins to the deadly form by touching them.

The animal, produced through genetic engineering, is still in its mother's womb and expected to be born early next year, Kirin officials said.

Kirin, which has previously branched out into pharmaceuticals, produced the cow after conducting joint research with U.S. biotechnology firm Hemateck LLC in Connecticut.

The two firms plan to use the cow to develop medicines for diseases such as hepatitis C, pneumonia and rheumatism, a Kirin spokeswoman said.

Although cows that are not immune to BSE could be used to produce antibodies for medical or pharmaceutical products, the firms feared that doing so would cause worries among consumers, the Kirin officials said.

Kirin had no plans to disclose the medical technology to any third parties including livestock producers, they added.

"Because there are ethical issues involving gene recombination, we have no intention of disclosing the technology," said a Kirin official. "We never do any gene recombination to produce anything that can be eaten."

A livestock industry official said it would probably be a long time before the technology would be used for mass production.

"This appears to be good news for livestock producers, but I think it will take a long time before cows immune to BSE can be produced on a large scale," said Soichi Kagawa, managing director of the Japan Livestock Industry Association.

"I think there will be a patent issue that could make it difficult for livestock producers to use that technology," he added.

BSE swept through British cattle herds in the 1980s, forcing the destruction of millions of cattle. Some people who ate contaminated beef have developed the human version of the disease, called variant Creutzfeldt-Jakob disease (vCJD).

The World Health Organization says 139 people have been diagnosed with vCJD and virtually all have died of it.

Japan has also had several BSE incidents, and has suspended all beef imports from its top supplier, the United States, since a case was discovered there in December.