Most feeding rules apply to all horses, not just specific breeds.
Horses are grazers. They can actually be eating, or foraging, for up to 20 hours a day. They need to in order to keep their guts functioning properly.
Horses bodies produce toxins used to help with digestion. Without food, these toxins are not digested and remain in the body and can cause serious problems, including liver faliure.
Pasture and good quality hay is all a horse really needs (unless supplementing for weight gain, energy etc etc of course!). They will eat as much hay as they need and this is easy to assess. If they dont leave any scraps behind after eating, then feed a little more the next time. Keep increasing until they're leaving little scraps behind. This is the horses way of saying thats all they need for that day.
If your horse is stabled at all then make sure he has access to some hay for the duration of time that he is stabled.
There's so much information out there on feeding, and it can be very intimidating. Stick to the basics and dont over complicate things.