"He beat nothing"

[Riot]

Originally Posted by AeWingnut

But Curlin didn't make his first start until he was 3 and went on to have a nice career. I don't recall hearing too much about soundness being a problem for him.

Obviously, not all horses unraced at two break down. But the breakdown rate has been quantitated, and is significantly greater in horses that don't race at two, than those that do.

In other words, horses that cannot get appropriate training and racing at two, when their bones are still remodeling, are measurably less likely to make safe, dense bone that holds together over a career.

I also said, "We also know there are clear limits to the type of work that is optimal for future soundness regarding speed and distance." Meaning one can not only underdo it, but overdo it, too. There are measurable speeds and distances that can be used in the training and racing of young horses that have been found optimal for being consistent with less breakdowns over a career.