The US Department of Agriculture has raised doubts about the effectiveness of the government's bovine spongiform encephalopathy (BSE) surveillance measures that were established in 2004 following the discovery that a cow in Washington state was infected with the disease in 2003.

The Office of the Inspector General has released an audit which states that it cannot determine whether safeguards are being adhered to in beef processing and slaughtering facilities. Moreover, the report highlights various weaknesses in the surveillance programme, such as its voluntary nature.

While conducting the review, it was discovered that the USDA misdiagnosed a Texas cow. Department officials, the audit said, had ignored calls from its scientists for more tests on the cow, which, it transpires, was indeed infected with BSE.

The inspectors said that high-risk cattle parts had not entered the food chain.

The department has undertaken steps to bolster its surveillance programme, including introducing the Western blot, a more sensitive test to detect the presence of BSE.

In response to the report, Dr Ron Dehaven, Animal Plant and Health Inspection Service (APHIS) administrator, defended the surveillance scheme.

"This is the largest BSE surveillance effort the United States has ever undertaken," he said. "This has been an extraordinary cooperative effort and has succeeded because of a shared spirit of dedication on the part of all partners in the effort."

"At the beginning of its report, OIG affirms that USDA has made significant efforts to implement the enhanced surveillance programme, including developing the necessary infrastructure, processes and controls, in a short amount of time. The report also acknowledges the Department's efforts to coordinate with other government agencies, industry and laboratory and veterinary networks to carry out the programme."