What is the number 1 cause of death in race horses?

Answer 1

Actually, colic, founder, and old age, same as every other horse, tend to be the top three. While there are many horses put down due to injuries suffered on the track, there are many more who are injured and survive, or who retire sound, especially since the number of horses injured keeps going down as the safety measures are increased.

Of those who do die as a result of a race-related injury? Generally it's caused by shattering a major bone - either the cannon bone or one of the bones in the ankle. Most of the time, surgery to repair those is too risky and too expensive, and there's no choice but to put the horse down.