During cooler weather, many folks consider feeding bran mashes to their horses. It has been believed for years that bran mashes would warm up the horses and have a laxative effect that would clean them out and prevent colic. However, Dr. Lori Warren indicates bran does not have a laxative effect and adding wheat bran to the diet did not soften stools. In fact, the moisture content of the stool was the same with or without the wheat bran. Wheat bran does increase the bulk of the manure, giving the appearance that the horse is being cleaned out, but this is not the case. The laxative effect was attributed to the fiber in wheat bran.
Human medical doctors recommend patients eat bran cereal or a bran muffin to keep regular but wheat bran is not a high-fiber food. In fact, wheat bran has about the same amount of fiber as oats and has less fiber than regular hay. The difference between people and horses is that humans have a diet that contains only about two percent fiber and a bran muffin may make a difference. However, the horse's diet is already about 35 percent fiber so a scoop of wheat bran will really have no effect. Although wheat bran is not a laxative, it is palatable for horses and it contains energy and protein similar to oats and thus should be thought of as a grain instead of fiber. One thing that is important to realize is that wheat bran as well as rice bran are high in phosphorus, and in horses high phosphorus decreases calcium resorption. Because of this, feeding wheat bran daily could cause a significant detrimental effect on your horse's health because it is not a balanced diet. Therefore, a wheat bran mash is not recommended or effective at preventing colic in horses.