Horses feeding question?

Are you worming them regularly? And who determined that they are overweight? A grazing muzzle sounds ridiculous to me...horses need to graze! Especially if you are not supplementing them with grain or hay. I would really consider the dry lot, then you could limit the amount of time they do get to graze. The most important aspect is obviously exercise. You could kill two birds with one stone if you could ride one while ponying the other. Good luck!