The Canadian Food Inspection Agency has issued an official best guess as to the source of the BSE crisis that has crippled the Canadian cattle industry.
In a summary of its investigation into an American dairy cow found infected with BSE last December, the CFIA said the cause was likely contaminated feed from a Canadian mill.
A similar hypothesis was put forward for the Alberta beef cow diagnosed with the same disease in May 2003.
The agency said it is probable the two animals at the centre of the BSE storm ate contaminated meat and bone meal made from cattle of British origin while on Canadian soil.
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Canada banned the practice of feeding ruminants to ruminants in August 1997, but the CFIA’s investigation has proven both animals were born a few months before the ban and were fed rations containing meat and bone meal.
“There is a plausible explanation when these animals might have been exposed to prions at a time prior to the ban,” said CFIA chief animal health veterinarian George Luterbach.
However, there is no way to definitively prove the theory be-cause no samples remain of what the animals were fed.
“We have no idea and we will never know whether the infectious prion was in that meat and bone meal.”
The cattle may have contracted the disease after the prohibition was put in place by eating feed from a mill that was breaking the rules, but Luterbach said investigators have found no evidence of non-compliance with the feeding ban.
As a result, the most probable explanation remains that they ate contaminated feed before it was outlawed. In its report, the agency also suggested a hypothesis about how the feed was tainted.
Between 1980 and 1990, Canada imported 192 cattle from the United Kingdom, which were placed under surveillance. In 1993 one of those imports was diagnosed with BSE near Red Deer.
Agriculture Canada subsequently destroyed or re-exported all the remaining animals that were under surveillance, but 68 had already died from natural causes or had been sent to slaughter.
Luterbach said one or more of those 68 could have contracted BSE and ended up in the feed supply.
“That is the most likely theory how BSE got into North America,” he said.
For that theory to hold true, there would have to be an “intermediary step” between the British cattle entering the feed supply and the two most recent cases of BSE because four years elapsed between the two events.
In other words, there were likely more infected animals along the way. Luterbach said the 1997 feeding ban would have put an end to that hypothesized chain of infection.
“The finding in May and the second finding in December is not likely to be the tip of the iceberg, but rather the residual effect of a practice that was recognized as being a risk and addressed in 1997.”
The agency is also investigating the imported animals, their herds of origin in the U.K., their slaughter and the resulting use of rendered material from those animals in Canada’s feed system.
