Bush had been speaking by telephone with Prime Minister Paul Martin about the Asian tsunami disaster. Martin took the opportunity of the call to raise the cattle issue.
The United States, Canada's largest beef-export market, closed its border to beef and cattle shipments in May 2003 after the discovery of Canada's first home-grown case of mad cow disease.
Washington, which has already permitted shipments of most processed beef, said on Wednesday it was satisfied with Canadian safety measures and now intended to reopen the border on March 7 to shipments of live cattle under the age of 30 months.
However, the next day, Canada said that initial tests had shown a 10-year-old dairy cow might have had the brain-wasting disease. A definitive test is being carried out now.
The cow was born before Canada's 1997 ban on using animal protein in cattle feed, which scientists say can transmit the disease.
"(Martin) indicated to the president that if the test result is positive, there is no reason this should impact the US rule process. This is an older animal and predates Canada's feed ban," the Canadian official said.