Japan has expressed opposition to a set of proposals related to mad cow disease by the World Organization for Animal Health, farm ministry officials said Wednesday.

The proposals included designating cow milk, bull semen and leather as materials free of the possibility of spreading the disease.

But in a letter sent to the Paris-based OIE, the Agriculture, Forestry and Fisheries Ministry said there are no new scientific data suggesting these materials are safe, the officials said.

The OIE proposed designating the materials as products that can be safely traded during its six-day general meeting that began May 23 in Paris. Separate proposals on mad cow and other animal diseases were also discussed.

The organization, which consists of top veterinarians from its 165 member countries and territories, meets every May to review its standards on animal health and safety.

Japan also opposed a separate OIE proposal to ease safety measures against mad cow disease. Under current OIE safety standards, brains and other body parts deemed to have a high risk of containing prions -- abnormal proteins believed to cause the disease -- should be removed from cows that are at least six months old.