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Colic in Horses: Preventing EnterolithsBy Kentucky Equine Research Staff · June 6, 2016

Horses have over 100 feet of tissue making up the equine gastrointestinal tract—much of it coiled rather precariously in the abdomen—explaining why colic in horses is so common. From impactions and displacements to torsions and foreign material, nutrition plays an important role in both preventing and managing painful abdomens.

Sand accumulation causes colic in many areas of the world as most owners are all too aware, but did you know stones can also form in the large intestine?

“Enteroliths are stones made from magnesium ammonium phosphate hexahydrate, also referred to as struvite, that can potentially block the flow of ingesta through the right dorsal, transverse, and descending colon,” explained Kathleen Crandell, Ph. D., an equine nutritionist for Kentucky Equine Research.

Although experts continue to be baffled by the exact cause of stone formation, some contributing factors are thought to include:

  • Feeding alfalfa hay;
  • Breed predisposition (horses of Arabian descent);
  • Spending ≤50% of time outdoors and lack of daily access to pasture grazing; and
  • Excessive dietary levels of magnesium, nitrogen, and phosphorus in an alkaline colon.

The stone forms around a foreign object such as a small stone, nail, pin, needle, coin, metal fragment, horse hair, cloth, or rubber that the horse has ingested. This object is referred to as the nidus, a Latin word meaning “nest.”

“Alfalfa hay contributes to alkalinization of the colon and provides an abundant source of magnesium, nitrogen, and calcium to the diet. Alkaline conditions within the colon enable magnesium, ammonia, and phosphorus to crystallize on a nidus, gradually allowing an intestinal stone to form rings, layer by layer,” wrote researchers from the Department of Large Animal Clinical Sciences, University of Florida College of Veterinary Medicine, in a recently published article on colic*.

Based on their review of the available literature on enteroliths in horses, House and Warren suggested the following nutritional recommendations to minimize enteroliths:

  • Eliminating excess magnesium;
  • Avoiding excess protein to minimize excessive nitrogen consumption;
  • Ensuring an appropriate calcium-to-phosphorus ratio;
  • Controlling the pH in the gastrointestinal tract; and
  • Eliminating alfalfa products from the diet entirely in horses with a history of enteroliths. Instead, offer an oat or grass hay and daily access to pasture.

Be sure to consider all aspects of your horse’s diet when thinking about magnesium and protein, including nutritional supplements, when assessing your horse’s diet. When in doubt, consult with an equine nutritionist.

*House, A.M., and L. K. Warren. 2016. Nutritional management of recurrent colic and colonic impactions. Equine Veterinary Education. 28(3):167-172.