The dairy cow in Washington state detected to have mad cow disease was almost certainly imported from Canada, the US Department of Agriculture said last night.
The US authorities had DNA evidence "that allows us to verify with a high degree of certainty" that the animal in question originated at a dairy farm in the Canadian province of Alberta, Ron DeHaven, the Department's chief veterinarian, said.
Canada's first case of mad cow disease came to light in the same province in May. Canadian officials said last night that their own independent testing also suggested the cow came from Canada.
But until 23 December, no case had been reported south of the border. Since then, the Bush administration has been frantically trying to trace the origins of the disease. In an effort to reassure foreign consumers and protect $3.5bn (£1.9bn) of annual US beef exports, the department announced that the month-old offspring of the infected cow, as well as 450 other calves in the herd, would be destroyed.