Andrew's girlfriend here again.
Tomorrow- I just meant that the growth plates on a 2 year old have not fully fused together, and that the joints haven't reached their mature strength. Sorry about that- should have been more specific. Their skeletal system simply isn't strong enough to handle the pressure that racing puts on them at such an early stage in their life, since that is the slowest maturing system in the equine body.
I agree that humans have been pushing the equine body for thousands of years, but you mentioned endurance horses. The stresses on endurance horses are totally different from the stresses on race horses- mostly respiratory and muscular, whereas the race horse ends up with structural stress as well. Plus, I know several endurance riders, and most of them wouldn't go on even a 15 mile ride with a 2 year old, let alone a 50 or 75 mile endurance race.
I know that the idea is that these horses mature earlier, but even in my admittedly short time in the horse industry (around 10 years where I have actually known what is going on), I have seen too many 'broken-down' off the track Thoroughbreds who were only good as pasture pets... and they were 9 years old. I can't help but think that if these horses were allowed to mature to even 3 years old before serious race training began, then the numbers of injuries and track rejects might decline a great deal. Personally, I think running them at that age has less to do with the horses being 'more mature' and more to do with greed and blindly following 'tradition'.
I don't think horse racing should be stopped- I enjoy watching races as well. It is just one more equestrian sport, and if one is ended, then it seems like they would all be in danger. Every equine sport has its issues (the eventing world has had its share in the past few months, as well). However, I do feel like the entire structure of racing could use a bit of an overhaul to ensure the welfare of the animals involved. While I agree that if we are concerned about horses, we should be concerned about the welfare of all species (I actually work in the field of farm animal welfare), I feel that the strains we place on horses are physically much more taxing than those placed on other species, and thus, they require a bit more regard from humans.
Also, I would be very interested in your book, once it is published. I'm always looking to expand my knowledge of the different disciplines. Please let Andrew know when it is ready to go!