3dayz wrote:
Just the scientific side of me looking at the other side of the correlation, but what if it is that the larger more successful farms(who most likely have better stallions/mares and better quality foals) all generally start their horses as long yearlings/2yr olds? And then those with less resources and maybe less quality foals, wait longer?

Not arguing the findings, I don't have enough knowledge in the field to do that. Just pointing out the findings are correlational and hence there may be other factors here. What I would like to see is a group of farms each split their herd into 2. One group they start as long yearlings, the others the wait a bit(groups are split randomly) and then see how the horses turn out.
I agree with you. Correlation is not the same as causation. And they do mention the possibility of other variables (Another is that physical conditions that may have prevented a horse from starting at 2, on average at least, never fully disappeared and their reemergence ended a horse’s career), but it's like a small typed clause on the back side of a contract. Only someone who pays attention to it will have noticed. PDJ for example will definitely say that this is 100% proof that riding yearlings is good for them and makes them stronger. The article is IMO written to support the 2yo races. On this board, I have always seen that people say that the money is in the 2 and 3 yo races and everyone who breeds for a race horse will try to get the horses ready for them. So if they can't get them ready, physical problems caused by training or even before training started are very plausible reasons why they won't be started. If a horse can't stay sound in pasture or in training, I say chances are big it won't stay sound in competition. Just my vieuw on this, without knowing who did the research, who financed the research (can tell you a lot about the content) and how they took the sample of horses. 

  

Trial-by-fieldwork distinguishes us from neighbouring tribes: the namby-pampy sociologists and social psychologists with whom we might be otherwise - God forbid - easily be confused - Kate Fox