This is a profit driven industry where horses are typically seen as expendable; they can be literally discarded and replaced when they don't make money. If a horse isn't fast enough to race, he may be sent to the slaughterhouse. Sometimes even previous champions who once earnt their owners millions of dollars in races can end up as horse meat if they slow down. This is the gruesome fate of around thousands of horses bred for racing each year.
WARNING: graphic content
If you love horses, please pledge to never bet on cruelty.