President Bush should demand the resignation of Agriculture Secretary Ann Veneman (search) because the department quietly allowed imports of some Canadian beef despite the ban it imposed due to Canada's case of mad cow disease, Sen. Kent Conrad (search), D-N.D., said Thursday.

"It now appears that the USDA (search) has secretly and selectively violated its own publicly announced ban on the importation of processed beef from Canada," Conrad said in a letter to President Bush. "In fact, the report is so damaging to the credibility and integrity of the USDA that I believe you should ask the Secretary of Agriculture to resign."

Alisa Harrison, a spokeswoman for the department, defended the agency's actions, saying the department had announced in August of 2003 that it would permit certain products that did not pose a risk to public health.

The secretary's office was called late Thursday for reaction to Conrad's call for Veneman's resignation, but no one was available to respond.

At issue are permits for beef from cattle under 30 months of age, which are considered at minimal risk of mad cow disease, also known as bovine spongiform encephalopathy (search), or BSE. Eating beef containing the misshapen protein which causes BSE has been linked to a rare but fatal brain-wasting disease in humans, variant Creutzfeldt-Jakob disease (search).

The department's August announcement said it would allow the imports of boneless beef — cuts from muscle — as exceptions to its general ban on imports of Canadian beef and live cattle. Muscle cuts were considered safe because the mad cow protein, when it exists, develops in other tissue, notably the brain and spinal cord.

The department imposed the general ban on imports in May 2003 immediately after Canada announced that BSE had been found in one animal. It allowed some exceptions in August.

However, critics of the department's handling of mad cow disease say the department, without telling the public, granted permits for Canadian processed beef products it had not listed in August.

Another Democratic senator, Tim Johnson of South Dakota, said the department's inspector general should investigate the permit controversy, but said he was not calling for Veneman's resignation "at this point."