Any owner, his authorized agent, or trainer of a horse which has been entered for a purse race and has been drawn in to the race and entitled to a post position or is also eligible, who does not wish such horse to start in the race, shall file a request for a declaration not later than the "scratch time" designated for such race by the stewards. Any horse so declared pursuant to such request shall lose all preferences it has accumulated.
Cal. Code Regs. Tit. 4, § 1602