The finding puts new emphasis above the border in the investigation of the North American outbreak of the brain-wasting disease. The Holstein, slaughtered in Washington state on Dec. 9, is the second cow born in western Canada diagnosed with mad cow disease since May.
The test results mean investigators will intensify their search for the source of infection, most likely from contaminated feed, in Alberta, where the Holstein was born in 1997.
The DNA tests on the cow, on one of its offspring and on the semen from the cow's sire, as well as records that show the cow came from a dairy farm in Alberta, make "us confident in the accuracy of this traceback," said Dr. Ron DeHaven, the Agriculture Department's chief veterinarian.
Dr. Brian Evans, chief veterinary officer of the Canadian Food Inspection Agency, said independent testing from a Canadian lab agreed.
Agriculture Secretary Ann Veneman announced the mad cow diagnosis on Dec. 23, the first time the disease has been found in the United States since its discovery in Great Britain in the mid-1980s.
Canadian officials had announced last May that a cow in Alberta, also born in 1997, had been diagnosed with the disease.
While no links have been found between the two cases, investigators will now focus on looking for common sources of feed, Evans said.
He added, "We have not got sufficient evidence to make any feed link between the two farms."
Canadian and U.S. officials believe the cows were probably infected as calves in Canada because they were born before August 1997, when both countries banned the practice of giving cattle feed that contained parts of cattle, sheep or other cud-chewing animals.
"We now have a likely explanation and source for their infection," DeHaven said.
The announcement prompted the U.S. beef industry to renew its call for resumption of international trade in American beef. More than 30 countries banned imports of U.S. beef after the Dec. 23 announcement.
At the same time, the Canadian government said it would begin an international marketing campaign for Canadian beef, banned after the May discovery. "We believe that we can go around the world and tell people we have a safe commodity," Canadian Agriculture Minister Bob Speller said.
Both countries have been pushing for a change in international standards that would allow trade to continue after a limited outbreak of the disease.
In Washington, however, some lawmakers said the DNA test was evidence that the United States should keep in place a ban on importing cattle from Canada that was imposed after the Canadian mad cow case. U.S. officials have been considering allowing the importation of younger Canadian cattle — unlikely to have the disease because of its long incubation period.
Senate Democratic leader Tom Daschle of South Dakota and Sen. Robert Byrd, D-W.Va., also asked for speedy implementation of "country-of-origin" labeling on most meat and produce that would clearly identify meat from animals that were born, raised and slaughtered in the United States.
DeHaven, however, refused to say that the mad cow problem belongs to Canada. The highly integrated cattle industries in both countries produced cross-border sales of live animals and animal products of more than $2 billion last year.
"It's a North American issue. Has been. Continues to be," DeHaven said.
Both countries are trying to locate the other animals from the Canadian herd. Records indicate that about 80 dairy cows entered the United States with the sick Holstein in 2001 and U.S. authorities have so far found 10 of her herdmates.
Evans also said Canadian records indicate that an additional 17 young cows were from the herd, including a calf by the infected animal that entered the United States at a later date. USDA officials said they are trying to confirm that.
U.S. officials have placed three Washington state herds under quarantine because of ties to the Holstein.
USDA announced Monday that it had decided to kill a herd of 450 calves in Sunnyside, Wash., because it included one that was born to the Holstein.
Officials said that particular calf was not tagged and could not be identified, necessitating the mass killing. They have said they can't rule out the possibility that mad cow disease can be transmitted from mother to calf.
Mad cow disease, or bovine spongiform encephalopathy, eats holes in the brains of cattle. The disease is a concern because humans can develop a brain-wasting illness, variant Creutzfeldt-Jakob disease, from consuming contaminated beef products.