Horses are generally companion animals in the U.S., like cats and dogs. So it's sort of sick to think of eating them, but you can find horse on the menu in France and other countries. The U.S. has slaughterhouses which have historically shipped horsemeat overseas for human consumption, as well as slaughtering them for dog food and other purposes. It's certainly a huge fear of people who have their horses sold that they are being sold to killers and slaughterhouses...and that does happen.
Two recent Court decisions at the federal appeals level are curtailing horse slaughter in the U.S., though the loopholes in the decisions are already being found. In January, a Court ruled that a 1949 Texas law banned the killing of horses for human consumption overseas. See here for an article on that ruling. Then, last week, a Court ruled that the USDA cannot inspect horsemeat for a fee. The USDA cut off funding to inspectors, but the work-around was that the slaughterhouses paid the inspection fees. The ruling in late March effectively shut sonw slaughter in the U.S., as slaughter cannot be accomplished without USDA inspection.
So, of course, the next loophole...the horses are now being exported to Mexico for slaughter there. See an excellent article on the subject here. The same article includes useful information on how to act to get something done about the problem that now exists of exporting horses for slaughter.
Congress has had bills pending to end horse slaughter and has refused to pass them. (The House did get one passed but the Senate didn't take it up). The Courts found legal grounds to stop the slaughter in other ways, over time, and now it's critical to pass the bills that would prevent the export of horses for slaughter. Only then will the U.S. stop contributing to the horse slaughter problem. While it's sad that any animals are slaughtered, for horses it's especially sad, because they are animals that are such wonderful ranch hands, hard workers, best friends, riding companions, and loving partners.