Siaga's gained about 25-50 lbs since I've changed up his diet and had his teeth floated. Considering all the changes we've made, I may never know what caused the issue in the first place, since we've treated him for parasites, both external and internal sorts, I've had his teeth floated, upped his grain intake (Well. I'm giving him 5 cups of timothy pellets along with 3 cups of grain, no sunflower seeds, a weight boosting supplement, a calming supplement to help keep him from burning off calories before he stashes them as fats and muscle, and an Omega-3 oil supplement.)
Anyways, he's almost back up to par, maybe another 50 lbs or so and he'll be back to normal.
The next cause for concern is that he has a reaaaaally thick layer of dandruff. Its thick, really flaky, and oily. In places, the winter hair is coming out faster and so those areas feel really gummy where the dandruff is more easily felt and seen. Boy needs a bath. A really good one. I also cut his mane short, to make scrubbing it clean easier.