No more than eight horses shall be allowed to start in overnight events upon which there is pari-mutuel wagering. No horse shall be entered in more than one event on the same program except when the conditions of the race provide that it shall be contested in two or more heats. Trailers may be permitted whenever nine or more horses are allowed to start under this section. No coupled entries shall be permitted in overnight events.
58 Pa. Code § 183.184