TOKYO - Japan confirmed its 13th case of mad cow disease Wednesday after a slaughtered Holstein tested positive for the brain-wasting illness, a government food safety official said.

The 8-year-old dairy cow in Nara prefecture, or state, was found to have the illness after an exam given by a state-run infectious disease research institute in Tokyo, said Seiichiro Minese of the Nara food safety office.

The cow's meat and organs had not gone on the market and officials said the meat processing center in western Japan where it was dismembered will be thoroughly disinfected.

The cow is the 13th to test positive for bovine spongiform encephalopathy, or BSE, in the country since 2001, when Tokyo began checking every cow that was killed before it entered the food supply.

Tokyo also banned the use of meat-and-bone meal - made from ruminant animal parts - in cattle feed. Authorities believe the outbreak was caused by meat-and-bone meal.

Eating beef from a diseased cow is believed to cause the fatal Creutzfeldt-Jakob disease in humans.

The latest discovery comes as Japan and the United States discuss testing standards that could lead to a partial lifting of Japan's ban on American beef imports. Japanese Prime Minister Junichiro Koizumi said Wednesday that more scientific research was needed before the beef trade could resume.

Tokyo prohibited all U.S. beef from entering Japan in December after a case of mad cow disease was discovered in Washington state. Japan insisted it would not lift the ban until the United States also instituted blanket testing for cows.

U.S. officials have balked at blanket testing of all cattle, saying it's too expensive and unnecessary. In addition, they say the tests are reliable only on cattle 30 months old or older.

Japan showed signs of relaxing its demand this month when the state-appointed Food Safety Commission announced that the country could import meat from untested cows 20 months old or younger without endangering public health.

President Bush and Koizumi discussed the matter in New York on Tuesday but did not set a timeline for restarting beef trade.

"U.S. and Japanese views still remain somewhat apart" on when trade could resume, Koizumi said Wednesday while attending the U.N. General Assembly's annual meeting.

However, Koizumi added that he and Bush agreed that a resumption should not be "unduly delayed," and consultations were continuing between the two sides.

Both sides are eager to strike a compromise to reopen the Japanese market to American beef. The country was the most lucrative overseas market for U.S. beef, which is much cheaper than domestic beef.

Japan bought $1.2 billion of U.S. beef in 2003, more than any other country, before halting imports.