Opponents of the Canadian horse-slaughter industry make the argument that harmful chemicals injected into the horses as medicine could slip into the food supply.
But it is really the images of the animals in the minutes before they were put to death at two Canadian slaughterhouses - videotaped sequences of horse being whipped, poked with electrical prods, and hung to bleed that were broadcast last spring on national television - that have prompted an outcry.
Across the country, people gathered outside an Alberta abattoir, a Toronto restaurant, a Vancouver butcher shop, and on street corners in a handful of other cities on Tuesday to demand the slaughter be stopped.
"When the undercover investigations came out, we all thought that horse slaughter would be shut down in Canada because of the cruelty that happens," said Emily Lavander, the organizer of the protests who also volunteers at a horse shelter near Alexandria in eastern Ontario.
"We're asking that Canadians write or call their MPs and demand that they support Bill C-544 to end the horse slaughter in Canada."
Petitions bearing thousands of signatures of people who support the bill were introduced in the Commons in the final weeks of September.
In fact, Bill C-544, a private member's bill drafted by Alex Atamanenko, an NDP MP from the British Columbia Interior, does not call for an end to the slaughter. Rather it aims to end the import of horses to be killed in Canadian abattoirs and of the export of the meat to markets in Europe and Asia where there remains a strong demand.
The slaughter of horses has been banned in the United States since 2007, so about 50,000 of the animals are sent across the border to Canada to be killed here each year.
Even Mr. Atamanenko acknowledges the bill isn't going anywhere. It was introduced in June, but because it is not government legislation, it is not being moved forward.
So it is effectively dead "unless our government in its wisdom decides to adopt it, which they can, or unless another member of Parliament wishes to take up the charge on behalf of all the folks who are protesting against the horse slaughter in Canada," Mr. Atamanenko.
The government is not likely to take up the cause.
"Unlike the NDP, who think they have the right to tell producers what they are allowed to sell, our government will continue to work to maintain the highest of food-safety standards and the humane treatment of animals," Agriculture Minister Gerry Ritz said Monday.
Mr. Atamanenko said he introduced the bill for food-safety reasons. Chemicals like phenylbutazone, an anti-inflammatory that is administered to most race horses but is considered harmful to humans, could end up in the food supply, he said.
Martin Appelt of the Canadian Food Inspection Agency said his agency has regulations that prevent that from happening and conducts regular tests for prohibited substances in horse meat. In addition, he said, the industry conducts its own tests as do the countries that receive the meat from Canada.
Not all horses are tested. "That would not be possible due to sheer volume," said Mr. Appelt. So statistically it is possible that some chemicals are slipping through the safety net but that is highly unlikely, he said. There has not been a positive test for phenylbutazone in years.