The weight limit.
No horse will carry more than 96kgs: 85kgs of rider, 2kgs of water, 5kgs of rider kit, and 5kgs of saddle and stirrups.
The penalty system.
Riders get time penalties if their horses don't recover at an acceptable rate monitor their Derby run, and if a pattern of poor recovery emerges the organisers can disqualify a rider on horse welfare grounds. Vet penalties are treated as a horse welfare issue first, and a race tactical issue second - we investigate why the horse has been compromised and seek to exclude the possibility that a rider is pushing his or her horses too hard. Two race referees are on the course monitoring how riders are riding throughout the Derby and can be dispatched to spy on riders who have racked up penalties. Riders can flag suspicions or evidence of abusive riding to any of the event crews on the field and are encouraged to do so if they see horse welfare being compromised in any way between horse stations.
No horse goes more than one leg.
Each horse is used just once on the Derby. Some will return home (most likely a reverse journey of 36kms back to where they started) without a rider on, same day, but this is very much a day in the life for a Mongolian horse, as they travel comparable distances just to graze, most days.