Officials investigating America's first documented case of BSE said yesterday that they had quarantined a second herd of cattle as they sought to contain the health scare.
The US Department of Agriculture said it had quarantined two calves born to the Holstein cow, which was confirmed this week as having BSE. One of those calves was part of the original herd - which is already under quarantine - while the second was traced to a 400-strong herd in a neighbouring town, where it was being fattened for market.
The department's chief veterinarian, Ronald DeHaven, said: "The reason for concern with these calves is that even though it is an unlikely means of spreading the disease, there is the potential that the infected cow could pass the disease on to its calves."
The real challenge for the experts, however, remains tracing the herd in which the infected Holstein was born, since the four-and-a-half-year-old animal probably became infected by eating contaminated feed. If that it is the case, it is impossible to estimate how many other animals may have been infected. The incubation period is between four and five years.
The infected Holstein, which was slaughtered on 9 December, was part of a herd owned by the Sunny Dene Ranch in Mabton, about 200 miles south-east of Seattle. The second herd is in the town of Sunnyside, 25 miles away. Both towns are in the Yakima Valley, a relatively poor farming community.
The owners of the Sunny Dene Ranch, Sid and William Wavrin, have refused to comment on the infected animal. It is all but certain that their entire 4,000-strong herd will have to be slaughtered so that the brains and spinal tissue of the other animals can be tested.
Sources involved in the investigation have indicated that they are focusing on two unidentified livestock markets in central Washington state where the infected cow was most likely to have been sold.
With two dozen countries having already suspended imports of US beef, an equally pressing task for federal officials is to calm consumer fears. The Department of Agriculture said yesterday it was dispatching a team of trade experts to Japan, the biggest single buyer of US beef, to begin talks on how to address concerns and attempt to resume shipments. Last year, Japan bought about $1bn (£570m) of American beef.
Although the federal government has banned animal feed that includes the brain or spinal cords of other animals, John Stauber, the author of Mad Cow USA, said that was not enough. "Here's the problem. The feed ban has been grossly violated by feed mills," said Mr Stauber. In one such instance, X-Cel Feeds of Tacoma, Washington, admitted earlier this year that it had violated regulations designed to prevent the spread of BSE.Reuse content