The food safety agency traced 156 cohorts, cattle from the birth farm born 12 months before or after the infected cow, completing the investigation.

Of the 156 cohorts, 38 were located alive on various Alberta farms. They were euthanized and tested negative for BSE. The remaining 118 animals had either died on other farms in the province or had been slaughtered, said Gary Little, acting senior staff veterinarian for the CFIA.

"We can't tell you how many would have been slaughtered for human consumption," Little said.

Most cattle are slaughtered for food between 20 to 22 months of age, when they are considered too young to display abnormalities related to mad cow disease, he said.

The CFIA does not have any health concerns regarding these animals, Little said.

All the cohort animals were traced back to locations within the western province of Alberta, Little noted.

"We didn't see any animals that were sent into the US," he said.

The fourth native mad cow finding last month, also spurred a feed investigation at the farm, retail and mill levels. The cow was born after 1997, when the Canadian government banned cattle from eating feed containing protein from cows and other ruminants such as goats and sheep, following Britain's mad cow outbreak.

The feed investigation was expected to be completed soon.

Canada's first native BSE case was confirmed on an Alberta farm in 2003, prompting countries around the world to shut their borders to Canadian beef and cattle. Trade has gradually resumed with strict regulations, with the industry having lost an estimated C$7 billion ($6 billion) by the time the US Department of Agriculture reopened the border to animals under the age of 30 months in mid-2005.