This is a very interesting thread, even tho it has contibuters like myself with no first hand knowledge of horse herds (or heards in the case of runners).
There are two aspects to the herd instincts that have not been directly addressed here:
1. I am not sure the horse considers the group in the race as his (her) current herd... rather the groom, trainer, and jockey are more important members of the horse's herd! ??
2. Dominant Stallions do NOT lead the rush from danger, they tend to trail and push along other herd members. So if you set a herd of horses off to race with out jockeys, the mares would finish first, and the dominant stallion near last.
I would guess that horses view a race is an activity of the small (personal) herd 'playing' against other herds. The running by the horse is done at the request of the jockey, who is associated with the trainer (the boss of the small herd). Some horses have the game better figured than others, and running talent helps.
To make racing more herd-natural we could change the game. Gather the competitors in a group at the starting area, then chase them around the track with a couple of mechanical cougars/lions mounted on Boss Hogg cadillacs (like dog racing in reverse). The winner in male races being the horse finishing immediately infront of the Caddies. The winner in female races, or for young males, will be the one in front of the pack. (then to keep it real, those horses passed by the Cadillacs will be sent to the Alpo plant! or maybe limited to lower class races, where the Caddy's cruse control is set lower by 1 or more speed points
)
Minimum race length=2miles .......... or maybe NOT!
I guess it won't sell in a big way!
I would be interested in the reaction to the numbered points above from Horse(wo)men who have spent time in the presence of horses, not just in the stands at the races.