How are the graded US races determined if their aren't the pre quallified races. For instance i have a grade 1 and a grade 2 race and the grade 2 has stronger horses. Is it random selection?

It seems as if purse puts a lot into it, like a million dollar grade 3 race will get a generally better field than a half a million grade 2. However, I have noticed that game breds that start racing and winning grade 1 races will only target grade 1 races from there on out. Generally though, grade 1 races will have the higher rated horses (and some lower rated horses if the race doesn't cap starters) unless there is a richer race that day that fits the horses conditions better (i.e. a 140 sprinter wont go to the l'Arc just because the purse is huge but would rather go towards the grade 3 sprint the same day)

Ok that helps a lot. Thanks MJ