Canadian officials have come under fire for a delay with tests in the country's first known case of mad cow disease in a decade.
The eight-year-old cow, from a farm in the western province of Alberta, was diagnosed with bovine spongiform encephalopathy, or BSE, on Tuesday - nearly four months after samples were taken from the slaughtered animal.
Officials from the Canadian Food Inspection Agency (CFIA) say the cow was sent to a rendering plant after the slaughter and did not go into the food chain.
But they said three farms - where the animal lived in the past three years - had been quarantined, and a 150-head herd at the most recent farm was being destroyed for testing.
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It's an isolated case
"
Canadian Prime Minister Jean Chretien
"At this point, it's a precautionary measure," Dr Claude Lavigne from CFIA said on Wednesday.
Officials said their investigation also included searching documents of owners of the animals, dealers who transported them and auction markets where they were sold.
In response to Tuesday's announcement, the United States - Canada's biggest market - banned Canadian beef imports pending full investigation into the case.
Although officials from US Department of Agriculture (USDA) said that if no more cases were found the ban would be lifted.
Australia, South Korea, Japan, Taiwan, New Zealand, Singapore and Mexico also banned Canadian beef imports.
'Low priority'
BSE has been linked to new variant Creutzfeldt-Jakob Disease (vCJD), a human disease that affects the brain and is invariably fatal.
Canadian Agriculture Minister Lyle Vanclief said the infected cow was slaughtered on 31 January and kept out of the food chain because it was believed to have pneumonia.
Dr Gerald Ollis, Alberta's chief veterinarian, said that because there was no suspicion of BSE then and the animal was not used for food the sample had a low priority.
"There was a focus on animals lined up to go into the food chain," Mr Ollis was quoted as saying by the Toronto Star newspaper on Wednesday.
High-profile steak
In western Canada beef production is a massive industry, with Alberta province alone selling about $3bn of meat last year - much of it to the United States.
The BBC's Ian Gunn in Vancouver says it would be a big blow if more BSE cases were discovered, as the Canadian economy is still feeling the effects of the Sars outbreak of last month.
However the Canadian Cattlemen Association said the incident appeared to be isolated, and sought to reassure consumers.
"BSE does not spread from animal to animal," it said in a statement.
"All the precautions are in place to prevent other cattle from being affected. The focus must be on determining how this one cow became infected."
On Wednesday, Canadian Prime Minister Jean Chretien tried to quell fears about the safety of the county's beef by eating a steak lunch in front of cameras.
"It's an isolated case. We hope this problem will not last long," he said.
It is the second reported case in Canada after a cow that had been imported from Britain tested positive for the disease in 1993, leading to the rest of its herd being slaughtered.
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