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WINNIPEG, Manitoba (Reuters) - Canada's 13th case of mad cow disease, discovered earlier this week, was born more than five years after Canada banned feed practices thought to cause the disease, the Canadian Food Inspection Agency said on Friday.
The Holstein cow, which was tested for the disease after it died on a British Columbia farm, probably consumed a small amount of infected feed in the year after it was born in 2003, said George Luterbach, a senior veterinarian at the CFIA.
"There probably was some small level of contamination that remained within the feed system when the animal was very young," Luterbach said in an interview.
More than half of Canada's 13 cases of bovine spongiform encephalopathy were animals born after 2000, despite the ban Canada put in place in 1997 after a European outbreak of the brain-wasting livestock disease.
But the fact that only 13 cases have been found, despite testing more than 220,000 animals most likely to develop BSE shows Canada's control measures are working, Luterbach said.
"We can tell by the intensive surveillance that the cases are not increasing," he said. "If the checks and balances were not working, one would expect (the disease) to become more common over time, and that's not the case."
The cow did not enter the human food or animal feed supply, the CFIA said, and did not pose a health threat.
The human form of BSE, known as variant Creutzfeld-Jakob disease, is believed to be caused by eating meat from infected animals.
The CFIA is going through records to try to determine what the cow ate and how it became infected, Luterbach said. It will also trace animals born on the same farm within a year.
Mad cow disease is believed to be spread when cattle eat protein rendered from brains and spines of infected cattle or sheep. Canada banned that practice in 1997.
But the material was still allowed in pig and poultry feed until July 2007, when regulators ordered that brains, spines and other risk material from old cattle be removed at slaughter and destroyed.
The CFIA has said the strict feed rules should help eliminate the disease nationally within a decade.
Canada has been deemed a "controlled risk" country for mad cow disease by the World Organization for Animal Health (OIE) because of its surveillance and control measures.
The new case will not affect that classification, Luterbach said.
The initial home-grown case of BSE in 2003 devastated the country's export-dependent beef industry after major buyers including the United States banned Canadian beef and cattle.
Trade has since gradually resumed with the United States, but access to other markets continues to be limited.
Reporting by Roberta Rampton; editing by Rob Wilson