Sand colic, digestive upset that stems from the chronic accumulation of sand and dirt in your horse's intestines, can strike any horse who lives on loose, sandy soil.
Horses pick up sand as they eat hay fed from the ground or graze short grass in pastures. The granules then settle to the bottom of the intestines, specifically in the large colon, where their grittiness can irritate the intestinal lining.
Mild sand colic, which is often accompanied by diarrhea, may be transient, but eventually enough sand can accumulate to result in severe, ongoing discomfort. In the worst cases, the intestines may become twisted or displaced or even rupture.
One way to tell if your horse is ingesting sand is to do the "mason jar test," also called the "fecal flotation test." Take six fecal balls from the middle of a fresh pile (this assures they are not contaminated with sand from the ground) and place them in a quart of water. Stir the contents, let the concoction sit for around 15 minutes and then check the container to see if any sand has settled in the bottom.
If more than a teaspoon of sand collects at the bottom of the jar, your horse is probably ingesting a potentially dangerous amount of sand. However, the absence of sand doesn't necessarily mean he's home free: It's possible that sand has settled in his gut and is simply not moving through the digestive tract. If your horse shows even mild signs of colic, call your veterinarian regardless of what you see at the bottom of the jar. Ultrasonic imaging can reveal an accumulation and aid in making a definitive diagnosis.
Removing sand from a horse's intestines can be difficult. Psyllium, a natural laxative, can help dislodge the granules, but surgery may be needed to manually remove large amounts of sand. It's far easier to keep your horse from ingesting sand in the first place by feeding hay off of mats rather than the bare ground and managing your pastures so that they do not become overgrazed. If you feed a psyllium supplement to prevent sand accumulation, be sure to follow the instructions on the label.