While Europe has struggled with mad cow disease, a fatal neurological ailment with no known cure, the United States and Canada have found fewer than a handful of cases. Since 1986, about 180,000 cases of the disease have been found worldwide, mostly in Europe.

Mike Johanns, the agriculture secretary, confirmed Friday that an older animal tested positive for the brain-wasting disease, sparking fears that foreign countries would shun American beef again at a time when Johanns was making a strong push to reassure export markets that U.S. beef was safe.

Officials from the Agriculture Department said Saturday that tests would be done on the cow's brain tissue at a department laboratory in Ames, Iowa, and at an internationally known facility in Weybridge, in Britain, to determine if the animal was infected with mad cow disease, or bovine spongiform encephalopathy.

The tests could take up to two weeks, Reuters reported a department spokesman saying.

Mad Cow Testing Program

So far, the department has revealed few details about the origin of the cow. A spokesman said Friday that the animal was first tested in November and that initial results were inconclusive. Another test was applied, and results were negative.

Then the Agriculture Department's inspector general, an independent group within the department, in reviewing the department's mad cow testing program, requested that the cow, along with two other previously suspect animals, be tested again using a different technology, known as "Western blot," that is used in Europe and Japan. The cow tested positive on Friday.

Uncertainty about the same cow caused beef prices to dip before, said Bill Bullard, chief executive of R-Calf USA, a cattle group that has been critical of the department's mad cow testing program.

After the department announced that tests on the animal in November were inconclusive, cattle prices fell $70 per head on animals costing about $1,000, resulting in $126 million in losses to the cattle industry over a three-week period, Bullard said.

Volatility in the Marketplace

"This uncertainty causes volatility in the marketplace that is detrimental to U.S. cattle producers," Bullard said. Confirmation that the animal had mad cow would make it more difficult for Johanns to reopen the border to live cattle from Canada, which he has said was a top priority.

The United States closed the border after mad cow disease was found in a Canadian cow in May 2003. Two more cases were confirmed in Canada last year.

While Europe has struggled with mad cow disease, a fatal neurological ailment with no known cure, the United States and Canada have found fewer than a handful of cases. Since 1986, about 180,000 cases of the disease have been found worldwide, mostly in Europe. Last year, Britain found 343 cases, and 535 cases were discovered across the rest of the world.