Dec. 1 (Bloomberg) -- Japan is examining a possible new case of mad cow disease that may delay an agreed resumption of some U.S. beef imports to Japan. Test results are due by week's end.

Local government officials are conducting follow-up tests on the 20-month-old steer from the northern island Hokkaido after an initial test on Nov. 29 detected the disease bovine spongiform encephalopathy, local dairy official Osamu Terada said today.

If confirmed, it would be the youngest mad cow in Japan and threaten an October accord resuming U.S. beef imports of cattle 20 months of age or younger. Japan, which banned all U.S. beef last year after a case of mad cow was found in Washington state, agreed to allow some imports because testing was thought incapable of detecting the sickness in younger animals.

``This news may lead to some renegotiation'' of the October deal, said David Kruse, president of CommStock Investments Inc. in Royal, Iowa. ``It is going to be an extensive long-term proposition to get the export market back to the levels of a year ago, even if the deal is not derailed.''

Another case of mad cow disease would be Japan's 15th. Meat from the current animal was not processed into food, Terada said. Five of the previous cases were also found in Hokkaido, according to Japan's agriculture ministry.

The U.S. is the world's largest beef producer. Its meatpackers slaughtered 35.5 million cattle last year, producing 26.3 billion pounds of beef, U.S. government figures show. Before the ban, Japan was the biggest overseas buyer of U.S. beef, importing $1.7 billion of the meat in 2003, according to the U.S. Department of Agriculture.

Australia has since grabbed 91 percent of Japan's beef market, up from 41 percent last year.

Cattle prices in Chicago fell from a 17-week high yesterday on speculation a positive test for a 20-month-old Japanese mad cow might derail the planned resumption of U.S. beef imports.

The U.S. discovered the Washington case of mad cow disease last December, and no cases have been found since.

BSE has been linked to a variant Creutzfeldt-Jakob disease, a brain-wasting illness blamed for at least 139 deaths in the U.K. The country killed millions of animals to eradicate the disease, which surfaced in U.K. herds in 1986.

To contact the reporter on this story: Issei Morita in Tokyo at imorita@bloomberg.net

Last Updated: November 30, 2004 23:01 EST