Canada and the US are co-operating to overcome a beef crisis after tests all but confirmed that the cow with the first US case of BSE was from Canada.
Three herds have been quarantined in Washington state
Officials from the US agriculture department said results showed a "high degree of certainty" that the cow originated at a dairy farm in Alberta.
The department has been investigating the case since the cow was found last month to be infected with BSE.
More than 30 countries have banned US beef since the announcement.
Correspondents say the results of the tests will allow investigators to intensify their search for the source of the infection.
More cases 'possible'
US Agriculture Secretary Ann Veneman announced the US case on 23 December.
Since the announcement, US government vets have been alleging that the cow was imported from Canada.
Up until now, Canadian officials have said there is not enough evidence for this claim.
But now Canadian chief veterinarian Brian Evans has said that the genetic tests seem to confirm the claim.
He said in a joint news conference with US officials that he could not rule out the possibility that more cases might be discovered during the investigation.
But he added that no link had been established between the Washington case and a single Canadian case discovered last May, also in Alberta.
Since the US announcement three herds in Washington state have been quarantined and the slaughter of 450 calves has been announced.
On Monday the US sent teams of officials to Mexico, Japan and South Korea to try to convince its trading partners that American beef is safe to eat.
Canadian Agriculture Minister Bob Speller also said on Tuesday that he would lead his own delegation to the same countries.
Scientists believe humans can contract a deadly brain-wasting disease by consuming beef products from cows with bovine spongiform encephalopathy (BSE).