IE 11 is not supported. For an optimal experience visit our site on another browser.

DNA test no proof of mad cow origin

DNA test results expected this week from the first U.S. case of mad cow disease may support the theory it was born in Canada but cannot provide absolute proof, a senior Canadian official said Monday.
/ Source: Reuters

DNA test results expected this week from the first U.S. case of mad cow disease may support the theory it was born in Canada but cannot provide absolute proof, a senior Canadian official said Monday.

If genetic markers in the DNA of the infected cow match those from a bull that records show is its sire, it will be a ”strong indication” that the cow came from Alberta, as U.S. investigators purport, said Paul Kitching, director of Canada’s National Centre for Foreign Animal Disease.

“You can never be 100 percent sure in this type of situation, but all the evidence taken together would be as certain as you’re ever likely to be,” Kitching said.

U.S. officials and industry groups have said they hope a match will allow a quick resumption in beef exports, which have been banned by most foreign buyers.

But Canadian farmers worry a match will mean a protracted closure of markets for their beef. Canada found its first home-grown case of mad cow disease in May, a discovery that crippled its export-dependent beef industry.

Ear tags tracked origin
U.S. officials fingered the cow as Canadian after finding ear tags at the slaughtering plant in Washington state where the infected animal was processed.

Canadian officials traced the ear tags back to a Leduc, Alberta dairy farm that sold off its herd in 2001. The farmer kept excellent records, including information about what semen was used to artificially inseminate cows on the farm.

Bovine paternity experts in labs on both sides of the Canada-U.S. border have extracted DNA from that semen as well as from brain tissue from the infected cow, Kitching said.

They will compare at least 12 genetic markers and as many as 21 in the two DNA samples, he said.

If the markers don’t match, the bull did not sire the cow, which means there could be a mix-up with the ear tags from the plant, or could mean the farmer’s records were wrong, or that the cow’s mother was inadvertently impregnated by a live bull on the farm, Kitching said.

“If they coincide, it’s a very strong indication, and taken together with the ear tags and supporting evidence, would suggest that they have made the match,” he said.

But many Holstein cows share genetic markers because farmers use semen from a relatively small number of high-performance bulls to impregnate many cows, Kitching said.

“These bulls are responsible for fathering a large number of calves,” he said. “It’s not quite as diverse as the human population, where one guy doesn’t father that many kids.”

Investigators could be more certain of the diseased cow’s origins if they had genetic material from her mother, but Kitching said it is not available.

Kitching said he expects Canadian and U.S. officials will compare their DNA results before announcing the findings.

A spokesperson with the Canadian Food Inspection Agency said Monday that if tests go well, results may be available as early as Tuesday.