WASHINGTON (AP) – The Agriculture Department says a central California dairy cow that tested positive for mad cow disease has what scientists say is an atypical case. The agency’s chief veterinary officer, John Clifford, said Tuesday the animal didn’t get the disease from eating infected cattle feed. Bruce Akey of the New York State Veterinary Diagnostic Laboratory at Cornell University says that means it’s “just a random mutation that can happen every once in a great while in an animal.” It is the first new case of mad cow disease in the U.S. since 2006 and the fourth ever discovered in the country. Health authorities say the animal never was a threat to the nation’s food supply. Baker Commodities executive Dennis Luckey told The Associated Press that the disease was discovered at his company’s Hanford, Calif., transfer station when the company selected the cow for random sampling.