BEIJING, Aug. 4 -- A third cow
suspected of having mad cow disease has tested
negative, the U.S. Agriculture Department said on
Following initial tests which suggested the possibility of infection, tests at a USDA
laboratory in Ames, Iowa, and at an internationally recognized lab in Weybridge,
England, showed the cow did not have the fatal disease, said John
Clifford, the department's chief veterinarian.
The suspect cow died on the farm in April where it was
raised after complications from giving birth. The farm's location has not been
There have been two confirmed U.S. cases of mad cow: a
Texas cow in June and a Canadian-born cow in Washington state in 2003.
Scientists say the brain-destroying disease is caused by
malformed proteins called prions. People can acquire a human version of the
malady by eating contaminated beef products.