Description

Enteroliths are stones that form in the intestines of the horse. Comprised of mineral salts that form around a small object, such as a stone, wood chip, or piece of metal or string, they may cause intermittent bouts of diarrhea, colic, and a depressed demeanor. This condition is known as enterolithiasis.

Structural and chemical composition analysis indicates that enteroliths are composed primarily of magnesium, ammonium and phosphate. When these three elements combine into a crystalline form along with feed materials and other minerals such as calcium, iron and aluminum, they can become large stones that do not pass through the horse's digestive system.

If the enterolith becomes large enough to become lodged in the small colon, the horse will show signs of severe colic. Enteroliths may also become lodged in the pelvic flexure or the junction of the large and small colon.

Horses often exhibit general colic signs with a mild to moderate degree of pain that increases as the large intestine becomes more distended with built-up gas.

If not caught and treated, rupture of the intestine may occur, causing the death of the horse.

Symptoms

• General colic signs with increasing pain
• Small enteroliths/stones passed in manure
• Lethargy
• Depression
• Cranky behavior
• Weight loss
• Occasional loose stool
• Poor performance
• Reluctance to jump or go down hill

Causes

Although no specific cause is recognized, diets high in alfalfa hay are seen as a risk factor. Excess alfalfa with high amounts of magnesium and phosphorous tends to alkalinize the normal acidic intestinal environment. This causes the minerals to precipitate and attach to foreign bodies in the colon, resulting in a higher pH in the large colon as well as a higher mineral content. Studies have found that nearly all horses with this condition have a diet of at least 50% alfalfa.

Cases of enterolithiasis are seen more frequently in some locations such as California, Florida and Louisiana, possibly because of the mineral content of the feed and water as it relates to the soil in these areas.

Genetic predisposition may play a role in the development of enteroliths. Arabians and Arabian crosses comprise a large proportion, approximately 40.3%. of the affected horses in studies. Other commonly affected breeds are Quarter Horses, Thoroughbreds, Appaloosas, Morgans and American Miniatures. Female horses have a higher rate of enterolithiasis than males.

Reduced motility of bulk feed material through the large intestine because of feeding management may also be a cause. Insufficient roughage in the feed may slow the passage of food through the intestines and provide a favorable environment for stones to form and grow.

Reduced activity and exercise and stall confinement can also affect the digestive process. In some cases, the type of bedding may contribute to the problem. Studies show that horses that have straw bedding have a lower incidence of the disease, possibly because straw is a high-fiber, bulk feed material that is low in phosphorus and protein and when horses nibble on it, the resultant digestive processes may be moved along.

Bran has been noted as a possible source of phosphorus for enterolith formation. Further research is being done to determine the true effect on horses prone to enterolithiasis.

Prevention

Veterinarians suggest that the alfalfa in a horse's diet should be held to less than 50%, with grass or oat hay being used instead. Increasing the grain-to-hay ratio will decrease the pH of the intestinal tract, keeping the intestinal environment more acidic.

Bran, with its high levels of phosphorus, should be reduced or eliminated from the horse's diet. Some veterinarians suggest adding 1 cup of vinegar to the horse's feed once or twice daily to help decrease the pH in the hindgut. Daily grazing should be provided, but if that is not possible, increasing feedings to 3 to 4 times daily can be helpful.

Consistent and frequent exercise to keep the digestive system moving is important, along with avoiding prolonged stall confinement. Straw or rubber mat bedding may help in avoiding enterolith formation. The areas where horses are kept should be swept clean and small articles should be put away so that the horse doesn't have access to small foreign bodies that it might ingest.

Treatment

Although small enteroliths will be passed in the manure, surgery is necessary to remove larger ones. For a horse in good physical condition, the success rate is 90-95%.  The surgery is rather expensive, running between $3500 to $5500, with most horses being discharged with costs in the lower range. Further research is being done into the feasibility of dissolution of enteroliths in horses via dietary and management changes.