Canada has reported a case of mad cow disease in the western province of Alberta - the first known case in the country for a decade.
Authorities stressed the animal did not enter the food chain
The eight-year-old cow, from a farm in northern Alberta, was diagnosed with bovine spongiform encephalopathy, or BSE, following routine testing after it was slaughtered, Canadian Agriculture Minister Lyle Vanclief said.
He was speaking in a news conference televised live across the country - an indication of how seriously the case is being taken.
It is the second reported 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.
The Alberta cow's 1,000-strong herd has been quarantined and will be slaughtered as a precaution, and any other cattle affected will also be killed.
The infected animal, which was killed in January, was sent to a rendering plant after slaughter.
"The animal did not go into the food chain," Mr Vanclief was quoted by the Associated Press news agency as saying.
US bans imports
BSE has been linked to new variant Creutzfeldt-Jakob Disease (vCJD), a human disease that affects the brain and is invariably fatal.
In response to Canada's announcement, the US Department of Agriculture (USDA) said it was to ban Canadian beef imports pending full investigation into the case, although it added that if no more cases were found the ban would be lifted.
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
Canadian Cattlemen Association
"The USDA is placing Canada under its BSE restriction guidelines and will not accept any ruminants or ruminant products from Canada
pending further investigation," US Agriculture Secretary Ann Veneman said.
She added that the US was to send a technical team to Canada to assist its investigation.
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."