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Medical Index
First Posted July 15, 2007
Nov 9, 2010


by Debora Johnson
Diseases that may be caused from dietary origins

Enteroliths are stones which form around a foreign object in the intestines of a horse, similar to a pearl's formation. The stones are composed primarily of struvite, which is a combination of magnesium, ammonium, and phosphate. The struvite crystals are laid down in concentric rings around objects such as sand, pebbles, plastic, twine, hair, etc. Smaller enteroliths are normally passed through the intestine and may be found in the horse's droppings. However, larger stones will result in fatal colic unless surgically removed.

  • Feed preferably grass hay. 98% of horses with enteroliths had a diet of 50% to 100% alfalfa hay.
  • Reduce or eliminate bran from your horse's diet. Bran provides high levels of phosphorus which may contribute to enterolith formation.
  • Increase your grain to hay ratio. This will decrease the pH level in the colon. Horses with enteroliths had high pH levels in their colons.
  • Add one cup of vinegar a day to your horse's diet. This will also decrease intestinal pH levels.
  • Increase feedings to three or four times a day. Infrequent feedings will reduce the movement of bulk feed material through the large intestine, which may provide a favorable environment for the stones to incubate and grow.
  • Provide daily exercise and avoid prolonged stall confinement which also contributes to reduced intestinal movement of feed.
  • Bed your horse on straw instead of shavings. Straw provides an opportunity for horses to nibble on a high-fiber, bulk feed material throughout the day that is low in magnesium, phosphorous, and protein.

Genetics may play a role in enterolith formation. A recent study showed that around 8% of horses with enteroliths had siblings affected. Also, it is known that the Arabian is the most commonly affected breed with a study showing that Arabians and Arabian crosses. Other affected breeds are quarter horses, thoroughbreds, appaloosas and miniature horses. Warmblood breeds seem to be affected less commonly than other breeds. Researchers at UC, Davis have identified three candidate genes that may be associated with enterolithiasis and this research may provide the foundation for discovering the genetic basis of the disease. If gene mutations can be identified, diagnostic screening methods may be developed to allow early identification of horses at high risk for enterolith formation.

The latest research indicates:

"A comprehensive statistical analysis revealed that feeding 50% or more of the diet as alfalfa, less than 50% of the diet as oat hay or grass hay, and lack of access to pasture grazing on a daily basis were significantly associated with enterolithiasis. Specifically, horses receiving more than 50% of their diets as alfalfa were 4.7 times more likely to have enteroliths, while horses receiving less than 50% of their diet as either oat or grass hay were five times as likely to develop the condition. Finally, horses with limited access to pasture grazing were 2.8 times more likely to be diagnosed with enterolithiasis.

In horses at risk for developing enteroliths, the authors recommend eliminating alfalfa, feeding grass or oat hay, and allowing daily access to pasture grazing.

The study, 'Evaluation of dietary and management risk factors for enterolithiasis among horses in California,' is scheduled to be published in an upcoming edition of Research in Veterinary Science. Contributing authors were Hassel; Aldridge, BVSc, PhD, Dipl. ACVIM; Drake, PhD, and; Snyder DVM, PhD, Dipl. ACVS."

Medical Index