Canadian officials have traced to two mills the feed that probably caused North America’s two cases of mad cow disease, one in Canada last May and the other in the United States in December.
The feed from the Canadian mills could have contained infectious protein from imported British cattle, said Dr. George Luterbach, an official of a mad cow working group in the Canadian Food Inspection Agency. He said Canadian law prohibits disclosing the identity of the mills.
Canada reported its only case of the brain-wasting disease in an animal on a farm in Alberta. The United States followed with an announcement that an animal in Mabton, Wash., had mad cow. Both animals had been raised on farms in Alberta. And both ate feed containing meat and bone meal while they were calves.
“Our best hypothesis was the animals were exposed by contaminated feed,” Luterbach said. He said the two infected animals did not eat feed from the same mill.
In both cases, the feed was given to the animals as calves just before Canada and the United States banned the use of cattle tissues in feed intended for cattle in 1997.
Luterbach said the feed could have contained tissue from infected cattle imported from Britain before Canada banned the importation of British cattle after a devastating outbreak of mad cow disease there.
Canadian investigators had performed mad cow tests on all they could find of the 192 British animals imported to Canada between 1980 and 1989, when Canada banned such imports, Luterbach said. The investigators followed the cattle until 1993, but could not find 68 animals that died or were culled, he said. Protein from those animals could have been processed into feed, he said.
“One or a small number may have had BSE,” Luterbach said. Mad cow is also known as bovine spongiform encephalopathy, or BSE.
The feed would have been shipped in large batches to individual farms and consumed in about a week, and would not have been widely distributed, he said.
