We might not have a good answer for every situation. The reason is that certain horses might be at greater risk than others because they are less discriminating eaters than other horses or have an underlying digestive disorder that predisposes them to impactions. The other important issue is sand access. If horses are fed in an area that is almost exclusively sand and little or no grass cover, they will be at greater risk of sand impaction for obvious reasons. However, based on research that I have done, good quality hay alone can be sufficient to remove sand from the horse’s colon.
If you do decide to eliminate the supplement, which could be a reasonable decision, you need to monitor your horse’s fecal excretion of sand. This is not a perfect test by any means but is simple and could be helpful. Before you eliminate the supplement, place a couple of freshly passed fecal balls in a plastic bag. Pick up the fecal balls with the bag after you turn back the open end to cover your hand and then turn those edges back. Add tap water, seal the bag, and mix the water into the fecal balls. Allow the bag and contents to stand, and if sand is in the feces, it should settle into a corner of the bag. This is the swirl test. Do this daily for a week while feeding the supplement.
You can repeat this after you eliminate the supplement and see if there is a change. If the horse eliminated more sand with the supplement, you might want to include it. If no change, continue without. Ideally this could be done for every horse but this might not be practical. In that case, just sample one horse that you think might be representative or might be your biggest concern.
David E. Freeman, MVB, PhD, Dipl. ACVS
Professor and UF Large Animal Surgery Service Chief
University of Florida
College of Veterinary Medicine
Large Animal Clinical Sciences