An Alberta dairy cow recently diagnosed with mad cow disease was likely infected by contaminated feed, federal regulators said Thursday.

The Canadian Food Inspection Agency (CFIA) launched an enforcement investigation last month after a 50-month-old cow from an Edmonton-area farm was found to be infected with bovine spongiform encephalopathy.

CIFA initiated the investigation because the cow was born after a 1997 ban was imposed prohibiting the use of cattle parts susceptible to the BSE in certain animal feeds. 

The agency said an incident involving banned ingredients at a feed supplier may have been the source of the infection.

"A particular incident was documented in one commercial feed facility that may have permitted the contamination of a single batch of cattle feed with prohibited material," CFIA said in a news release Thursday.

"The entire batch of feed was shipped to the BSE-positive animal's farm. This particular batch of feed is the most probable source of infection."

According to the agency's report, two feed operations received prohibited materials from a rendering plant implicated in previous mad cow disease investigations. The report said the investigation is examining the operations at the feed mills.

The agency said no part of the infected cow entered the human food chain or animal feed system.

On Wednesday, CIFA confirmed another case of BSE in an Alberta cow, the fifth this year.

The agency believes that in the latest case the animal was likely exposed prior to the food ban or during the early stages of its implementation.

Nearly 120,000 cows have been tested for mad cow disease since the feed ban was imposed.

With files from the Canadian Press