Canadian animal health inspectors accidentally approved the export of a 31-month-old cow to the United States, violating strict US safeguards to prevent mad cow disease, a US Agriculture Department official said.

The mistake prompted a Wisconsin meat plant late Friday to recall voluntarily 1,856 pounds of beef that may contain the backbone of the imported cow.

The USDA said some of the meat may have already been consumed.

"It is very, very unlikely that this product would cause illness," said Steven Cohen, spokesman for USDA's Food Safety and Inspection Service. "We are still investigating how much may still be available and if any retailers received it."

A USDA official said this was the first violation since the United States reopened its borders last month to young Canadian cattle. The two-year ban was imposed after Canada's first domestic case of mad cow disease.

The United States prohibits the skull, spinal cord and vertebral column from domestic and imported cattle older than 30 months of age in the food supply. These materials are considered the most risky for spreading bovine spongiform encephalopathy (BSE).

Cohen said the adult cow did not show any signs of sickness when imported into the United States.

Green Bay Dressed Beef in Wisconsin processed the meat on Aug. 4 and distributed it to wholesale distributors in Pennsylvania, Florida, Illinois, Maryland, Minnesota and Wisconsin.

The products were sold under the American Foods Group and Dakota Supreme Beef brands and had an establishment number 410 on each box.

PREGNANT COWS

Canadian officials discovered the mistake during an investigation into a shipment of 35 animals from a southern Ontario farm to the Wisconsin slaughterhouse which included eight pregnant cows, said Francine Lord, national manager of imports and exports with the Canadian Food Inspection Agency.

US import regulations do not allow imports of pregnant cows, although Lord noted there were no food safety risks involved.

"For us, we take it very seriously," Lord said. "We deal with the US all the time, and it is clear that there is a low tolerance (for errors.)"

The agency is now investigating how the veterinarian verified the age of the cow, which is usually done with information from the animal's ear tag or by checking its teeth.

"We want to be sure that the vets are doing their job right," she said.

A total of 15 pregnant animals have been detected in five shipments from Ontario and one shipment from Western Canada, Lord said. The three veterinarians involved with the shipments were suspended from certifying exports until the agency completes its investigation, she said. (Reuters)