Washington ? A Canadian official acknowledged that his country held onto samples from a cow infected with mad cow disease for four months, possibly allowing potentially sick cows into the food chain.

Dr. Claude Lavigne, a top official at Canada’s animal products directorate, said officials were searching for other cows infected with the disease, also known as bovine spongiform encephalopathy.

“At this point, it’s a precautionary measure,” he said Wednesday in a teleconference.

On Tuesday, Canada said it found a cow had been sick with mad cow disease, a brain-wasting illness. Officials got the test results four months after taking samples from the cow at a rendering plant.

U.S. and Canadian officials have said none of the infected animal went into the food supply.

Canada still is looking for where the 8-year-old cow was born and other cattle, including newborn calves, with which it may have been in contact. The disease can incubate in a cow for up to eight years.

Sen. Byron Dorgan, D-N.D. said Canadian officials should have promptly checked samples and released the results.

“Somehow it took four months to have it tested and to tell the people in this country and also in Canada there was a cow with mad cow disease killed in January,” Dorgan said. “That’s absurd.”

Although Canadian and U.S. officials have declared that the food supply is safe, Consumers Union said the two governments cannot guarantee that.

Quarantined cattle graze in a field on Stan Walterhouse's farm near Tulliby Lake, Alberta, Canada. Walterhouse said he was told Wednesday by a veterinarian that his herd was under quarantine. He said federal officials got his name because his brand was on the cow detected with Canada's first case of mad cow disease in a decade.The infected cow was at Walterhouse's farm in 1998.

“That’s exactly what they said in Britain, and now nobody trusts the government there,” said Mike Hansen, a senior research associate at the U.S. consumers group.

Mad cow disease sickened herds in Britain in 1986, killing more than 2 million cows. It also was linked to 130 human cases of Creutzfeldt-Jakob disease, the human form which causes paralysis and death. Scientists believe humans get it by eating meat from infected cattle.

Canadian veterinarians took samples of the infected brood cow on Jan. 31 at a rendering plant. They suspected the cow had pneumonia — a belief that led to the long delay in discovering that the animal had mad cow disease, said Dr. Gerald Ollis, Canada’s chief provincial veterinarian.

Samples were sent Feb. 8 to the Edmonton laboratory.

“They sat there until we had time to process them,” Ollis said.

The lab checks samples from livestock destined to be made into food and then tests those taken from euthanized and downed animals.

The United States imported nearly 1 billion pounds of Canadian beef and 1 million head of cattle last year, according to the National Cattlemen’s Beef Assn. The group’s chief executive, Terry Stokes, said he believed Americans should be confident that their food was safe because the U.S. government routinely tests for the disease.