A second potential case of mad cow disease in the United States cast doubt on whether the Bush administration could regain crucial Asian markets that have shunned U.S. beef.

The U.S. Agriculture Department said late Friday that it had found bovine spongiform encephalopathy, or mad cow disease, in an animal that had tested negative in November. This would be the second case of the fatal, brain-wasting disease found in a cow in the United States, and the fifth in North America since 2003.-_-