Dreamcatcher- I will look into some Ultium. Would I feed that in addition to Strategy if I ditched the Senior? Or is it an either/or kind of thing? Your blanketing practices for your mare sound exactly like what my vet outlined for Drifter at our last talk. I just had never considered that in his case. He is still fairly young and was in great shape heading into winter. I will NOT be making the no blanketing mistake again. Poor guy.
Yep, you just add the Ultium to the Strategy, I started with 1/2 lb per feeding, maybe in your case just do it at 2 feedings to start and then go to 3 and then 4. I worked my way up to about 5 lbs total per day, in addition to free choice grass hay and Strategy. If your horse's desired weight is 1250 lbs, then I'd feed him for 1500 lbs to start. At 1/2% of body weight, that would be 7.5 lbs per day, plus 1-2 lbs of Ultium per day.
Most vets are not nutritionists, and I'm not either so take my advice with a grain of salt. I have had MUCH better luck when feeding up a skinny horse if I keep it simple. I give free choice grass hay, Strategy and Ultium. If your vet was afraid he might not be getting all the vits and minerals he needs, you can add something like Clovite or Moorman's Gro Strong. I found it was counter productive to feed too many things, I.e. Alfalfa pellets, cubes, Sr, Strategy, Ultium, etc etc.
Another feed I've had good luck with is Purina's Omolene 400, it's designed to be a complete feed and would solve any vitamin and mineral issues, but it's a high percentage of beet pulp, so he might not care for it. It's worked wonders on hard keepers and the odd really thin horse I've taken in to rehab.
I also use Fastrak or Probios to help with digestion, and since he's had a history of ulcers, that might be a good thing to add. He may be having trouble getting the nutrients out of the feed, rather than not enough feed or getting run off of it. Just brainstorming here, not trying to 2nd guess your vet.