Washington ? Agriculture Department officials said Friday they had located another cow in Washington state believed to have entered the United States in the same herd as the Holstein that was recently diagnosed with the nation’s first known case of mad cow disease.

The newly identified cow has not shown signs of the disease, but its current herd has been quarantined as officials look for 80 other cattle that came into the U.S. from Canada with the diseased animal, said Ron DeHaven, chief veterinarian for the U.S. Department of Agriculture.

The animals entered the United States on Sept. 4, 2001. Finding them is “critical,” DeHaven said, because they may have eaten the same contaminated feed as the sick cow.

That cow could have consumed contaminated feed because it was born before the United States and Canada banned feed containing cows’ own nervous system tissue. Such tissue can carry mad cow disease.

Some of the cows quarantined since the U.S. case of mad cow was detected last month will be destroyed because of possible exposure to the infection or to quell public fear, DeHaven said.

“It would be safe to assume that some or all those animals will need to be sacrificed,” he said. “Even though we know with a very good degree of certainty that there’s no direct disease spread animal-to-animal, simply being on the same farm there are some public perception issues related to those animals.”

Of the other cows in the herd from Canada, nine went to the same farm in Mabton, Wash., as did the diseased Holstein, which was slaughtered Dec. 9 and tested positive for mad cow disease two weeks later. Those nine cows have been quarantined, DeHaven said.

The cow identified Friday is on a farm in Mattawa, Wash., he said.

DeHaven said the original Holstein was likely infected in Canada, because the incubation period for the disease is three to five years. He said feed was the “likely source of infection” for the Washington state cow, as well as for the Canadian cow diagnosed in May.