But tests revealed no horse meat in its meatballs or frozen beef burgers, it said.

In the United States, Congress effectively prohibited the slaughtering of horses for human consumption in 2007, by denying the use of federal funds to inspect horses destined to become food, a 2011 Government Accountability Office report said.

The legal maneuver does not preclude horse owners from selling to slaughterhouses in Canada and Mexico, and the GAO said in a report that many Americans have taken advantage of that opportunity.

"From 2006 through 2010, U.S. horse exports for slaughter increased by 148 and 660% to Canada and Mexico, respectively," the report said. "As a result, nearly the same number of U.S. horses was transported to Canada and Mexico for slaughter in 2010 -- nearly 138,000 -- as was slaughtered before domestic slaughter ceased."