Investigators continue to look for about 70 cows that could have come to the United States from the same farm in the Canadian province of Alberta where the sick Holstein was born in 1997. Suspicion focuses on those animals because scientists believe feed containing protein from infected animals is the most likely source of transmission of the disease.
Transmission from mother to calf also cannot be ruled out.
Mad cow disease, or bovine spongiform encephalopathy, is a threat because humans can develop a similar brain-wasting illness, a variant of Creutzfeldt-Jakob disease, from eating contaminated beef products.
Agriculture officials have insisted that the US beef supply is safe, but they nevertheless recommended a recall of more than 10,000 pounds of meat from the sick cow and other animals slaughtered with it on Dec. 9.
USDA officials said the parts most likely to carry infection -- brain, spinal cord, and lower intestine -- were removed before the meat from the infected cow was cut and processed for human consumption.
Most of the meat went to suppliers and stores in Oregon and Washington, while small amounts reached California, Idaho, Montana, and Nevada. In all, 570 meat distributors, stores, and restaurants received the recalled beef, but USDA officials said yesterday they did not know how many pounds of beef were returned.
Some probably was consumed in the 14 days between the animal's slaughter and the mad cow diagnosis, they said.
While consumer confidence in US-grown beef has not declined noticeably, foreign markets remain closed to it amid a debate about the extent of restriction necessary to protect countries from potentially tainted meat.
The World Organization for Animal Health, which sets international trade standards for animals and animal products, said total bans on beef from the United States and Canada, which also had a mad cow case last year, might go too far.
"An importing country cannot be more trade-restrictive than necessary to achieve the desired national level of protection," the group said. "Its measures must not be different from those applied to products within the domestic market."
The decline in beef exports is expected to lead to a $5.5 billion, or 10 percent, decline in net farm income in 2004, according to Global Insight, an economic consulting and forecasting company.
Japan, the largest importer, wants the United States to increase significantly the number of cattle tested.US officials have rejected testing at anywhere near the level the Japanese and some US consumer groups want.
