I wouldn't let someone else ride my horse except for the person I paid to ride.
I would tell the trainer to put the horse on a break for 3 days and make up those rides at the end of the normal 30 day training period. Or he can knock off the 3 days of training he didn't do from the bill.
He is giving you 27 days of his training for a 30 day training charge. You are paying for this specific trainer's skill. Not someone elses.
And those who were seen dancing were thought to be insane by those who could not hear the music