Please be careful. The horses I saw ay several different riding "stables" were in horrible condition, extremely thin, saddle sores like none I've ever seen. I'm a horse trainer and I have to admit the first horse I saw at one of the riding stables I mistook as a very sorry donkey, at second glance I realized that poor soul was an incredibly emaitiated horse, tacked up and ready for a rider. I wouldn't dream of getting on one of those poor creatures... I would be surprised if most of them could handle a walk, never mind a canter.
So please, if you go and find the horses thin, or tack up all day, or covered with sores, reconsider what you're doing.