Couldn't see a current picture of him. Can you post one??? Is he overweight, underweight or what???
I feed my 32" gelding this: 4-5 cups soaked beet pulp, 2-3 cups 4-way grain, 1/2 flake morning hay and 1/2 flake hay at night. My gelding is an easy keeper (in my avatar), but you'll have to adjust their feed to how much work he's getting and just watch his back. Most horses lose weight on their back first and its the hardest to get weight back on there (pasture is the easiest to put it back on).
Exercise is most important to get that "show" look. You'll want your horse toned (he may need a neck sweat). I would lunge him 15 minutes a day. You can put trot poles down to make his workout harder or to just mix it up. Also practice him in other areas he may be trained in (driving, jumping, obstacle, halter).