Animals from a second quarantined herd with ties to the Washington state cow with mad cow disease (search) will be killed, U.S. agricultural officials said Friday.

Dr. Ron DeHaven, the Agriculture Department's (search) chief veterinarian, said authorities soon will begin killing 129 dairy cows from the same Mabton, Wash., farm that was the last home of the infected cow.

Among those cows are nine Canadian-born cows that entered the United States along with the diseased Holstein. Investigators can't eliminate the possibility that the other 110 animals also came from the same dairy farm in the Canadian province of Alberta and were part of a group of 81 cows that came to this country in 2001, DeHaven said.

"They were potentially exposed to the same feed source as" the infected cow, DeHaven said. Scientists believe that contaminated feed is the main transmitter of mad cow disease.

The cows will be tested for the disease and their meat will not enter the human or animal food chains regardless of the outcome of those tests, DeHaven said.

In their ongoing search for the Holstein's Canadian herd mates, investigators believe they have located another seven cows at a dairy, DeHaven said. That would bring to 18 the number of cows officials have located in the two and a half weeks since the mad cow diagnosis.

Authorities on Tuesday killed a herd of 449 bull calves, which included an offspring of the infected cow. Agriculture officials said the herd had to be killed because the calf born to the sick cow was not tagged and could not be identified. They have been unable to rule out the possibility that mad cow disease could be transmitted from mother to calf.