The U.S. Agriculture Department said Monday that in August 1997 the two countries banned the use of brain and spinal cord tissue in cattle feed.

However, the diseased cow's owner checked has determined the animal was born in April 1997, said Ron DeHaven, the department's chief veterinarian.

"It is a likely explanation as to how this animal would have become infected," DeHaven told CNN.

Mad cow disease, known to as bovine spongiform encephalopathy, or BSE, is a brain-wasting disease usually transmitted to cows by contaminated feed and has an incubation period in animals of four to six years.

The U.S. Agriculture Department is awaiting DNA samples from the cow to confirm the animal originated in Canada, DeHaven said.

Locating the cow's birth herd will allow them to track down the herd's other cows to see if they might have eaten the same contaminated feed, DeHaven said.