Two U.S. consumer groups yesterday urged the United States to delay reopening its border to young Canadian cattle due to concerns that Canada may find more cases of mad-cow disease.

However, Canada's agriculture minister said that a second case of the disease discovered in Canada last week poses no threat to human health or trade and that the United States has assured Canadian officials it will not block beef imports, which are scheduled to resume in March.

"Canada has a strong regulatory regime in place to protect against the spread of BSE," Minister Andrew Mitchell said, referring to bovine spongiform encephalopathy, or mad-cow disease. "From a public-health perspective, this finding does not threaten the safety of Canadian beef."

Canada reported Sunday that an 8-year-old dairy cow in Alberta tested positive for the brain-wasting illness, confirming preliminary test results released last week. The cow did not enter the human or animal food supply, Mitchell said.

Despite the new mad-cow case, the Bush administration said it would stand by its decision to renew imports of Canadian cattle younger than 30 months in March, citing a World Health Organization study that even if 11 cases of mad-cow disease were discovered in the 5.5 million-head Canadian cattle herd every year, they would pose a minimal threat to human health. Two cases have been discovered in Canada, and the first U.S. case, in Mabton, Yakima County, in December 2003, involved a cow born in Canada.

"This case gives us great concern that the incidence of BSE may be more prevalent in Canada," said Tony Corbo, legislative director for the group Public Citizen.

"I think lawmakers should ... delay this rule until we get a clearer understanding of what's happening in Canada," said Joe Mendelson, of the Center for Food Safety.