U.S. health officials immediately banned imports of cattle, beef, beef-based products and animal feed from Canada, the Food and Drug Administration said.
Canadian Agriculture Minister Lyle Vanclief told a news conference Tuesday at the Alberta provincial legislature in Edmonton that the 8-year-old cow from a farm in northern Alberta was slaughtered on Jan. 31 because of suspected pneumonia.
Routine testing failed to rule out bovine spongiform encephalopathy, or BSE, and further testing in England confirmed the finding on Tuesday, Vanclief said.
"The herd has been quarantined. A trace on the animal is being done," he said. "The animal did not go into the food chain."
A previous case in Canada, in 1993, involved an animal born in Britain that was imported, he said.
Authorities have quarantined the farm and will "depopulate" the herd that the new case is from, along with any other herds that come into question, Vanclief said.
They will also trace the origin of the cow and how and where it was processed as part of an investigation into any possible spread of the disease, Vanclief said.
Alberta is Canada's main cattle province, with almost 40 percent of the industry. Hundreds of thousands of heads of cattle are exported to the United States each year.
The 1993 case, involving an animal from Britain, resulted in a herd being destroyed with no further spread, Vanclief said.
"I am not happy to be here today for this reason," VanClief said.
No case of mad cow disease has ever been found in U.S. cattle, despite intensive testing for the disease. To help prevent its spread here, the U.S. government routinely bans the import of meat and livestock from countries where mad cow disease is found.
The FDA and U.S. Agriculture Department are working with Canadian officials to get more information about the sick cow, including records concerning its past ownership and what animal feed it was given.
Mad cow disease, known scientifically as bovine spongiform encephalopathy or BSE, first erupted in Britain in 1986, and is thought to have spread through cow feed made with protein and bone meal from mammals. The FDA outlawed the feeding of mammalian meat and bone meal to cattle, sheep and goats in 1997, a rule considered the nation's main defense against mad cow disease.