I believe natural death do occur on every animals at a particular time frame which is tied to the life cycle and humans were not left behind on this as well, a horse naturally is well known for deriving pleasure specifically while running than anything, engaging horses on sport race shouldn't be a discouragement because they were not forced into the running but its what they derive pleasure doing.

I will like emphasize on the care and maintenance for those horses as animals cant talk but have developed a good sense of humor by making some particular signs and sounds whenever they wanted to pass an information across, the role of the vet and animals psychologist could be added advantage when their professionalism is adequately provided to racing organizations for the welfare and wellbeing of horses, there are times the animals as well develop weakness whenever they are unfit for an exercise, this as well indicate their own right against indiscriminately abuse  of using them.