Confirmation of a second U.S. case of mad cow disease resulted in immediate economic consequences -- Taiwan announced it would reimpose a ban on American beef -- while rattling ranchers who were assured USDA testing procedures for the brain-wasting disease were the "gold standard."

U.S. Agriculture Secretary Mike Johanns said Friday that the diseased animal, born and raised in the United States, was not used for food. But the USDA is working to locate herdmates and offspring of the affected cow, because they may also have eaten contaminated feed, and could possibly have mad cow disease.

The cow in question was slaughtered in November 2004, and tested positive in two initial screenings.

At the USDA lab in Ames, Iowa, immunohistochemistry (IHC) tests found no evidence of mad cow disease. But two weeks ago, after prompting by the USDA's inspector general, the cow was retested using a different method known as the Western blot test.

Those results were positive, and the USDA sent the animal's tissue to the world's foremost testing facility, in Weybridge, England, where the results were confirmed.

The nation's first known BSE case, in December of 2003, was confirmed using both the IHC and Western blot tests. In subsequent testing of other suspect animals, the USDA dropped the western blot test, while assuring the cattle industry that it was using the most definitive procedures available.

The group Consumers Union sent letters to the USDA in January and February, asking the agency to upgrade its protocols to match those of Japan and Europe, and to test all suspect cattle using both the IHC and western blot tests. In March, a USDA undersecretary sent a letter saying the agency would not use both tests.

Officials say they're now upgrading their protocols. Any animals that show up positive in initial screening will undergo two additional rounds of testing, using both the IHC and Western blot methods.

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