A mature bull from Alberta has tested positive for mad cow disease, or bovine spongiform encephalopathy, becoming Canada's ninth confirmed case since 2003.

The animal died on a farm last week and tested positive for the disease. Its carcass is under Canadian Food Inspection Agency control and no part of it entered the human food or animal feed systems, the agency said Wednesday.

The agency did not reveal where the animal was found or how old it was.

"Where the animal is found at the time of its death is not as important as where it lived in its first year of life," said George Luterbach, the agency's senior veterinarian for Western Canada.

He said the agency is searching for animals born within a year of the bull that may have been exposed to the same feed source as the infected animal.

"These animals are removed, destroyed, tested and disposed of in a manner that they do not enter the feed system," Luterbach said.

Scientists believe cattle can become infected with mad cow disease if they eat the tissue of an animal that had the disease. A ban on using cattle remains in feed went into effect in Canada in 1997.

The Canadian Food Inspection Agency, in a written statement, said the infected bull may have been exposed to a very small amount of infectious material, most likely during its first year of life.

The first case of mad cow disease confirmed in Canada was in 1993 in a cow imported from Britain. That was it until 2003, when BSE was identified in an Alberta cow. Since then, eight other cases have been identified, including the bull identified on Wednesday.

In 2006, five infected cattle were found in Canada, including a cow born years after safeguards were adopted to prevent the spread of the disease.

Humans who eat meat contaminated by mad cow disease appear to be at risk of contracting a form of the rare and deadly brain disease Creutzfeldt-Jakob disease.

Mad cow disease is linked to the deaths of about 150 people worldwide, most of them in Europe during an outbreak of the disease that peaked in 1993.

There have been three cases of mad cow disease reported in the United States.

The U.S. closed its borders to Canadian cattle exports when Canada reported a case of mad cow disease in May 2003. The border re-opened to beef from younger cattle a few months later, with young live cattle allowed across beginning in July 2005.

The U.S. has proposed opening its borders to Canada's older live cattle, a plan under public review until March 12.

Luterbach doesn't expect the latest case of mad cow disease to affect the proposed plan.

"We are open and transparent with the United States," he said. "We do not expect that this [latest case] will negatively impact any of the planned measures proposed."

Canada has close to 13.5 million cows and calves, with about 5.7 million, or 42 per cent, in Alberta. Canada's total beef exports amount to $2.2 billion annually.

With files from the Canadian Press