Such a link could solve the mystery of how the first U.S. case of the disease occurred. It would also go a long way toward calming the fears of some two dozen nations that have halted $3.2 billion in annual shipments of U.S. beef, according to experts.
The diagnosis of mad cow disease in an animal in rural Washington state last week sent cattle prices skidding by nearly 20 percent and forced the Bush administration to ban the use of sick or crippled cattle in human food, a measure long opposed by the meat industry.
Consumer groups and some Democrats have expressed skepticism about whether that and related regulatory changes go far enough.
U.S. Agriculture Department investigators hope to complete DNA testing early next week to confirm their suspicions that the infected Holstein cow was born in Alberta, Canada, in April 1997. Canada reported its first case of mad cow disease earlier this year in a Black Angus cow, also from Alberta.
Ron DeHaven, USDA\'s chief veterinarian, said investigators want to find out if the two animals might have eaten livestock feed from the same source.
\"Whether or not it came from the same plant ... is certainly relevant,\" he told reporters this week. \"The information that the Canadians have, with regard to the tracing of this feed, is very preliminary.\"
Canadian officials said they were poring over farm and feed mill records dating back eight years.
Mad cow disease is spread when cattle eat feed containing the remains of infected cattle. Canada and the United States banned the use of cattle remains in cattle rations in 1997, the same year both diseased animals were born.
While the USDA investigation into the cause of the mad cow case continues, the Bush administration is trying to restore the confidence of international meat buyers.
U.S. officials will fly to Mexico City this week to urge Mexico to reopen its border to American beef. Officials will discuss what the United States is doing to control the disease, Javier Trujillo, head of the Mexican agriculture ministry\'s animal health commission, told Reuters.
Mexico is the second-largest importer of U.S. beef.
Earlier this week, a U.S. trade delegation visited Tokyo and Seoul to urge both nations to allow beef exports to resume.
The National Cattlemen\'s Beef Association and the American Meat Institute want the White House to make resumption of beef exports a top trade priority.
Another problem for exporters is the fate of 44,000 tonnes of American beef, valued at $350 million, that was in transit to other countries at the time the first case of mad cow was discovered. All the meat is in limbo due to the trade bans.
\"These containers of highly perishable product are being held hostage on the high seas because our trading partners closed their borders,\" said U.S. Meat Export Federation President Philip Sent.