The US Department of Agriculture confirmed yesterday (13 March) that a third case of bovine spongiform encephalopathy (BSE) has been detected, in an Alabama cow.

The animal in question returned an inconclusive result on a rapid screening test performed on Friday, leading USDA officials to perform further tests. The animal was buried on the farm and did not enter the human food chain, officials said.

The USDA has launched an investigation into the herd history of the cow, as the animal had resided on its most recent farm in Alabama for less than a year. Officials are also attempting to locate the cow's birth cohort - animals born in the same herd within a year. Evidence suggests that the infected cow was older than 10-years, officials said, meaning that it was born before US regulations governing the content of animal feed came into effect.

USDA chief veterinary officer John Clifford said that he did not expect the positive result to have a negative impact on trade negotiations to resume export of beef to Japan. "We would not anticipate that this would impact our ongoing negotiations," he commented. "Our product is safe, we've got a number of interlocking safeguards. Japan itself has had 20-plus cases of BSE and we believe their product is safe with regards to the safeguards in place in that country."

Despite the US Government's reassurances, the news has had a negative impact on shares in the country's largest beef processor. Following the announcement yesterday, shares of Tyson Foods fell 4.3% to close at US$13.07 per share.