Meowy Catkin
Meow!
He has hay overnight in the field but I can ask if we can put a big bale in there because no the grazing isn't great atm, though should be on better grass soon when they rotate.
I think that this explains why he is light. He would look a lot better if he'd had ad lib hay all the time this winter. There isn't any grass in the field that's shown in the photo. Get him on ad lib hay now.
CPT is right, you are going to have to walk the tricky line between feeding him so that his condition improves and keeping him from getting laminitis.