Bran is a by-product of milled grains that can provide additional bulk and fiber in a horse's diet.
Bran is high in protein and can serve as a mild laxative. However, it is also high in phosphorus, a nutrient that can prevent calcium absorption and trigger bone-related problems in horses that eat excessive amounts.
Therefore, bran should not be fed to young horses, whose bones are developing; nor should bran comprise more than 10 to 15 percent of the diet of a healthy adult horse.
A wheat-bran mash, consisting of bran and hot water, has traditionally been recommended for horses that are old, sick, or dentally disadvantaged. It is also fed in sub-zero temperatures to ensure healthy bowel functions.