I would still blanket, it isn't them being on or off the track that affect the way their body works with warmth. (hopefully that makes sense) Especially if he is thin to begin with, his body doesn't have the fat to keep warm. My mare gets the alfalfa when she is out of the stall or I know it's going to be a cold spell.
Can you talk to the barn manager/owner to explain that you horse needs more to eat? Or can you sneak a flake when you are out there? :) hehe
Oh another thing to try if they won't feed more hay, get alfalfa cubes ... then you can feed them whenever you want :)
I have really found that the blanketing has helped my mare keep her weight on, even tho I am in CA and it doesn't get that cold- she needs it.
:: Karley ::
Tucker WB/TB- 11 yr
Speedy QH/TB- 22 yr