Canada confirmed on Tuesday its sixth case of mad cow disease and said it would investigate where the cow was born and what other animals may have eaten the same feed.

The Canadian Food Inspection Agency said test results confirmed what was suspected last week. The animal was at least 15 years of age, and was born before Canada implemented restrictions on potentially dangerous feed in 1997.

The agency said it was launching an investigation.

Mad cow disease is believed to spread through feed, when cows eat the contaminated tissue of other cattle. Humans can get a related disease, variant Creutzfeldt-Jakob Disease, in similar fashion — by eating meat contaminated with mad cow. There have been more than 150 human deaths worldwide linked to the variant.

Two of the six confirmed mad cow cases in Canada have involved animals that were infected after 1997, when a ban was instituted on the use of cattle parts in feed for cattle, or other ruminants such as sheep and goats.

The agency says Canada's food supply is safe, and the level of mad cow disease in the national cattle herd is very low. Canada has an estimated national herd of 17 million cattle.

U.S. Agriculture Department spokesman Ed Loyd said last week trade was resumed with Canada with the assumption that more mad cow cases would be found. Loyd said U.S. officials have "a high level of confidence in the safeguards and mitigating measures in place in the U.S. and Canada."

George Luterbach, an animal scientist with the Canadian Food Inspection Agency, said the latest case should not have any repercussions internationally.

"It is unwelcome news but not necessarily unexpected news," Luterbach said, adding "it should have little or no implications internationally."

Having tested 60,000 cattle last year, Luberbach said the agency is confident that mad cow is not a common in Canada or something that is growing.

Shipments of live cattle to the United States were halted in 2003 after the first reported mad cow case in Canada. Trade in young animals resumed last year, but there has been no word on when the border may be reopened to older animals.

Hugh Lynch-Ftaunton, president of the 90,000-member Canadian Cattlemen's Association, said some Asian and European countries may wait to see the final report on the latest case before reopening their borders to Canadian cattle.

"Some of the countries that are on the verge of dealing with us differently will probably want to study the report on this and that might slow it down marginally but I don't think it's going to be make or break," Lynch-Ftaunton said.

Last month, Canada announced it was broadening restrictions on animal feed in an effort to fight mad cow disease. The Agency revealed measures, to be phased in over the next year, aimed at keeping potentially risky cattle parts from all animal feed, not just feed destined for cows.

The parts will also be banned from pet food and fertilizers to avoid the risk of inadvertent cross-contamination of feed on farms and ranches.