A couple of excerpts from the article I just linked, to refute a lot of the crap posted in this thread:
***The industry promotes the false image of race horses retiring to lives of luxury as pets, well-cared-for riding horses, or stud horses. In reality, when horses can no longer race, they are usually sent to slaughterhouses. **
Rather than allowing a horse to rest long enough to heal completely, many owners and trainers decide the horse does not have race-winning potential, and they sell the horse at auction. From there, the horses are either sent to a slaughterhouse that ships horse meat to the European and Japanese market, or into abusive situations at the hands of new owners who may think they would like a retired racehorse, but forget about horses’ longevity and the expense necessary to maintain them properly. The United States alone slaughters tens of thousands of horses every year, of which many are ex-race horses.
Horses are sent to slaughterhouses in cramped trailers, usually without access to water or food. Injuries are common. A University of California, Davis study of 306 horses destined for slaughter found that 60 of them sustained serious injuries during transport. Some travel in double-decker trailers designed for cattle or sheep, vehicles not tall enough for horses, though the U.S. Department of Agriculture banned the use of these trailers for horse transport. Horses are subject to the same method of slaughter as cattle, but thrash about to avoid the pneumatic gun that should render them unconscious before their throat is slit.
Every year, around 300 racehorses die on British race tracks as a result of a.) fatal falls or serious injuries, most often breaks to the legs, backs, or shoulders, b.) heart attacks, or c.) a drop in performance that makes them not profitable. In addition to the hundreds raced to death, thousands more are killed or abandoned to neglectful or abusive situations every year because they can no longer run fast enough to be profitable.
**Ex-racehorses who are not euthanized often suffer an even worse fate. **
In the U.S., around 5,000 horses leave racing every year, the same number who enter it. Very few enjoy a decent retirement. Some are shot within weeks of their money-earning days coming to an end. A small number become breeders. Many are slaughtered, their bodies sold to countries like France, where people eat horse meat, or they end up as pet food. Others are exported, or sold from owner to owner into increasingly abusive and neglectful situations.*