How sure are they the cow has not entered the human food chain yet?
Mad Cow Disease Confirmed In California Dairy Cow, USDA SaysThe USDA has confirmed that a case of mad cow disease was found in a California dairy cow. It is the fourth case of mad cow, or bovine spongiform encephalopathy (BSE), found in U.S. cattle since the first in December 2003.
USDA Chief Veterinary Officer John Clifford said Tuesday afternoon that the cow did not enter the human food chain and that all U.S. meat and dairy supplies are safe. Further mitigating the risk to the public, milk does not transmit BSE.
According to the USDA, the animal's carcass is being held under state authority at a California rendering facility and will be destroyed. "It was never presented for slaughter for human consumption, so at no time presented a risk to the food supply or human health," Clifford said.