Wheat bran is the husk of the wheat kernel that remains after the starch has been removed from the kernel..., 

Wheat bran is rich in minerals and B vitamins. The starch content is low and the fiber content is high.  This positively stimulates horses' intestinal movements. Bran has a calcium-to-phosphorus ratio of 1:8, this can help straighten out the calcium-to-phosphorus ratio when feeding calcium-rich products, which is why bran is also often mixed under beet pulp. Bran is high in phosphorus and low in vitamins. Bran also has a binding capacity for endotoxins.