A case of mad cow disease has been found in a dairy cow in central California, John Clifford, the USDAs chief veterinarian, told reporters today in a briefing in Washington. The animal was found at a rendering facility, Clifford said. Its meat did not enter the food chain and the carcass will be destroyed, Clifford said. This is the fourth confirmed case of the brain-wasting disease in the U.S. cattle herd since the first was discovered in December 2003 in an animal that came from Canada.