Any Trainer or Assistant Trainer of a horse which has been entered in a race who does not wish such horse to participate in the draw must declare his/her horse from the race prior to the close of entries. Any Trainer or Assistant Trainer of a horse which has been drawn into or is also eligible for a race who does not wish such horse to start in the race, must scratch his/her horse from the race prior to the designated scratch time. A scratched horse loses all preference previously entitled to. Every horse drawn in for a post position shall have a Jockey named to ride such horse by scratch time. The declaration or scratch of a horse from a race is irrevocable.
Okla. Admin. Code § 325:25-1-16