Helena, Mont. ? A cow found to have mad cow disease in Canada once belonged to the same herd as five bulls shipped to Montana six years ago, but it’s highly unlikely any became infected, health officials said.

State authorities said Wednesday that the five bulls had since been slaughtered, but it was not known what happened to the carcasses.

None of the animals ever showed signs of the disease, said Karen Cooper, spokeswoman for the Montana Department of Livestock.

Ron DeHaven, a spokesman for the U.S. Agriculture Department’s Animal and Plant Health Inspection Service, also played down fears, noting negative tests so far on other animals linked to the infected cow.

The slaughter would have occurred after the Food and Drug Administration had banned the use of animal parts in livestock feed. Given that fact, DeHaven said, it is unlikely the meat would have been fed to other cattle.

He added that the chance of someone getting the human form of the disease from the five bulls was “immeasurably small.”

Two weeks ago, Canadian officials disclosed that a cow in Alberta had been identified as having the disease. The United States immediately banned all imports of Canadian beef and cattle.

Canada has since ordered the slaughter of more than 1,700 cattle in its effort to determine the disease’s source. So far, 800 animals have tested negative, including animals that had been in the same herd as the infected cow.

Canadian authorities said Wednesday that some of the bulls from Alberta apparently were subsequently resold in South Dakota and Montana.

Mad cow disease was first diagnosed in Britain in 1986. The human form is the fatal brain-wasting illness variant Creutzfeldt-Jakob disease. Scientists believe people get it by eating some meat products from infected animals.

Canadian Prime Minister Jean Chretien shows that Canadian beef is safe by having it for lunch at an Ottawa restaurant in Ontario, in this May 21 file photo. Increased concerns of mad cow disease have been prompted by North America's first case in a decade.