A 6-year-old cow from an Alberta farm has tested positive for mad cow disease, officials said Monday.

Dr. Brian Evans, Canada's chief veterinary officer, said the affected animal had not entered the human food or animal-feed systems.

The announcement came after the Canadian Food Inspection Agency spokesman, Mark Van Dusen, said Sunday that officials were testing a "suspicious sample."

Mad cow disease is the common name for bovine spongiform encephalopathy, or BSE, a degenerative cattle nerve illness linked to the rare and fatal human nerve disorder Creutzfeldt-Jakob Disease.

Canadian ranchers who were hit hard after the United States banned cattle imports from its northern neighbor in May 2003 following the country's first case of mad cow disease. The U.S. border reopened to young Canadian cattle in July.

U.S. Agriculture Secretary Mike Johanns said Monday that the United States will not cut off cattle shipments from Canada.

"I anticipate no change in the status of beef or live cattle imports to the U.S. from Canada under our established agreement," Johanns said in a statement. "I am confident in the safety of beef and in the safeguards we and our approved beef trading partners have in place to protect our food supply."

Industry officials said the cow's age meant it could have contracted the disease by eating feed left over after a 1997 ban on the use of cattle parts in feed.

Evans said a broad and extensive investigation was under way. He said the experiences of other countries show that very small amounts of feed purchased before the ban may have been retained on farms and lead to infection many years later.

"The fact that this animal would have been infected after the 1997 introduction of our feed ban is notable, but it is also consistent with the experiences observed around the world where BSE has been detected and where feed bans have been implemented," Evans said.

Stan Eby, president of the 90,000-member Canadian Cattlemen's Association, said a minuscule amount of banned feed could have been left over and could be been responsible for the latest case. But he said the matter certainly will be debated with Canada's trading partners.

Eby said Canada has tested 87,000 cattle and that four cases of mad cow disease have been found in Canada. Another cow exported to the United States also tested positive.

"It's certainly unwelcome at this stage," Eby said. "Hopefully, by the end of the day we'll know what these countries are going to do."

Canadian beef also recently returned to some supermarket shelves in Tokyo following the lifting of a two-year ban on imports. Japanese officials agreed to allow beef from North America back into the marketplace — provided it came from animals under 21 months.

Entry into Japan is considered key to the long-term recovery plan of Canada's battered beef industry. The scare has cost the industry $5.7 billion.

Cattle officials have pinned their hopes on a growing appetite from Pacific Rim countries to help reduce the reliance on the U.S. market, which consumes the vast majority of this country's beef exports.

More than 150 people have died of the disease, most in the United Kingdom, where there was an outbreak in the 1980s and 1990s.