Check his teeth and put him in front of decent hay non stop, have the vet do a fecal parasite check. I feed molasass free beet pulp, alfalfa pellets, barley and oats combined, and when I need to add weight to a horse I add calf manna pellets or rice bran, depending on the situation. Many people don't like grains, and everyone will tell you different. If I want a horse to gain weight instead of upping feed I add an extra feeding, keep that belly full and working keeps the horse warm and we don't burn calories keeping warm that way.
I also blanket in the cold because it preserves energy that would be used creating warmth.
Unless he's stellar quality papered, and a proven working horse in his career field geld him, his life will be easier and it may reduce some stress he's creating in himself when mares come into season- and as a result May make him an easier keeper.
Posted via Mobile Device