Once he gets regulated on his thyroid medicine weight should come off..Excessive weight gain is one of the symptons of hypo thyroid. I had a shep/huskey mix who was hugh at 115 lbs. But when he was diagnosed with hypo thyroid he was 145lbs. also had a 19 lb beagle that had reached 30lb. Both of them slimmed down in no time once on the medicine. They were both a little over 7 years old when diagnosed. The medicine is lifetime, but not expensive at all.