Bran does not actually clear out a horse's system at all. I started reading up about nutrition, and what to feed and stuff, so I could be more aware of what my horse should be getting, and one of the things I had been told for years was that I should feed a bran mash once a week or so, to clear out the horse's system, and that it would also help if they've got mild colic. According to the book Understanding Equine Nutrition by Karen Briggs, bran does nothing in terms of clearing out a horse's system, and though there is no harm in feeding a horse a bit of bran, there is no nutritional value in feeding them bran. To clear out sand, use a psylium (I know I spelled it wrong). You just put it in their feed, the package has all the dosage information.