You have to be very careful feeding Bran, especially mashes because they really provide no nutrition to the horse and actually will leach minerals out of their bodies.
Horses seem to like bran mashes, especially when mixed with apples or carrots, but beyond being a diuretic, there is no food value. PEOPLE love the smell, idea of gving horse such a "treat" in cold weather. Horse then loses even more moisture from body, when he may not be drinking enough to begin with in the cold weather. Bran fed with any regularity, often, causes horse body to lose important minerals and liquids he needs.
If you wish to feed warm treats, get some wet beet pulp made up, which WILL provide more liquids, food value to horse. AND even fed daily, it benefits the horses as a forage feed. You can certainly add cut apples, cut carrots, grain, to wet, hot, beet pulp making it an even more appealing food for the horse.
Is there any reason your horse can't have hay? At this time, most grass is not that nutritious, not growing, so horse needs other forage food to fill his digestive system. Various kinds of hay will be the most helpful in creating body heat as it is processed in the digestive process. You will keep a horse warmer in winter by feeding quantities of hay, over grain rations.
Horse also NEEDS to be drinking water, not just eating snow, so tank or buckets have to be liquid for best health results. If horse doesn't drink much, he is likely to dehydrate and often develop colic, a general term for digestive problems, as he tries to process his dry foods.