If a horse's droppings are loose, dry bran can help bulk up the stool or if a horse is constipated, damp bran acts as a mild laxative. Pour enough boiling water over it until it is dampened. Add a tablespoon of salt and mix very well. Loosely cover and feed when cool enough to eat. A bran mash is particularly popular in the winter time, especially when fed while still warm.
Some people like to add molasses, grated carrots or applesauce for flavor.
Particularly after hard work, a pound of boiled oats or barley can be mixed in. I have a 12 year old warmblood mare who is stabled in a box stall during the night and turned out most of the day. It can get very cold in the stable over night, enough to freeze her water bucket solid. Since I ride her all winter I usually trace clip her to allow her to cool out after her workouts. Any information on this subject would be helpful.