Canadian health officials said Thursday that tests have confirmed a seventh case of mad cow disease, in a 50-month-old dairy cow from Alberta.
"The entire carcass has been incinerated and did not enter the human or animal feed systems," the Canadian Food Inspection Agency said in a posting on its Web site.
The agency said it has located the birth farm, and investigators are tracing other cattle born there within a year of the affected animal's birth.
The animal's age means it contracted the disease -- also known as bovine spongiform encephalopathy -- after the 1997 feed ban intended to halt such cases.
CFIA said it will investigate how it might have been exposed and has invited U.S. officials to participate in the effort.
"While the United States and Canada have a strong system in place to protect animal and human health, the diagnosis of BSE in an animal born roughly four and half years after the implementation of the 1997 ruminant-to-ruminant feed ban does raise questions that must be answered," Agriculture Secretary Mike Johanns said in a written statement.
"We need a thorough understanding of all the circumstances involved in this case to assure our consumers that Canada's regulatory system is effectively providing the utmost protections to consumers and livestock."
The animal's age "does raise questions," the spokesman said. "We would like to have answers."
The Canadian government last month tightened its regulations on animal feed, and sought Monday -- when preliminary tests indicated the cow was a suspect case -- to downplay the risk.
"The safety of Canada's food supply remains protected through the removal of specified risk material (SRM) from all cattle slaughtered for human consumption," it said. "SRM are cattle tissues that have been shown in infected cattle to contain concentrated levels of the BSE agent. This measure is internationally recognized as the most effective means to protect the safety of food from BSE."
But Caroline Smith DeWaal, food safety director for the Center for Science in the Public Interest, called the report "troubling."
"This is a very young cow to be infected with BSE," she said in a telephone interview. "The animal would have been born five years after this feed ban was implemented, so I think this is a troubling new finding, and one that would certainly indicate the failure of the feed ban in Canada."
Most other animals that contracted the disease were born before or around the time of the national ban, she said.
In April, the Canadian government confirmed a case of mad-cow disease in a cow in British Columbia.
The country's surveillance program has now detected seven BSE-infected animals since it was put in place in 2003.
In March, Alabama officials announced the third case of mad-cow in the United States.