ice man said:
been going to the track for years and I almost feel dumb asking this question. But why do they have to put the horse down. I know it can't race anymore. I always heard it had something to do with a horse can't heal a broken leg?
I found this
The most striking difference between horses and other species is the blood supply. To heal any broken bone there must be a vibrant, healthy blood supply. Sometimes the blood supply to the bone is augmented by surrounding muscles and other soft tissue.
The lower leg of the horse has no muscle to provide any extra blood supply and often in these high-velocity racing injuries the bones are so severely damaged that the bones' blood supply is also destroyed.
A damaged blood supply means the injury cannot heal even if there is surgery to repair the bone. In human surgery this leads to limb amputation. Because horses need to stand evenly on all four legs, amputation is not a realistic or viable option.