See -
Horse Meat
Horse slaughter in USA

In the USA, legislation has been forced through by monied interests who sentimentally anthropomorphise horses, and insist on imposing their views on others (not unlike many other moralistic issues in the USA, unfortunately). Interestingly, the legistlation is strongly opposed by those actually involved in the industry, such as the American Quarter Horse Association. Politicians, afraid to stand up to little girls crying about ponies, caved.