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Enteroliths are stone-like mineral masses that can form in a horse’s intestinal tract. The term comes from “entero” (intestine) and “lith” (stone). These formations are made primarily of struvite, a compound consisting of ammonium, magnesium, and phosphate.
While smaller enteroliths may pass naturally in manure without issue, larger enteroliths can become trapped in the gut and eventually cause serious digestive obstructions often presenting as colic or even requiring emergency surgery.
Enteroliths usually form when a foreign object such as a small stone, piece of wire, or baling twine is accidentally ingested. If it’s not passed through the gut, the horse’s body attempts to neutralise the irritation by coating the object in a mucoid mineral layer, much like how an oyster forms a pearl around a grain of sand. Over time, layer upon layer builds up into a stone-like mass. However, not all cases involve a clear foreign object. In some horses, enteroliths may form without any identifiable cause. Research suggests that factors such as diet, genetics, and gut pH may all play a role.
Several conditions are believed to increase a horse’s risk of developing enteroliths:
Diets high in lucerne (alfalfa) hay or chaff may promote enterolith formation. Lucerne’s high protein content can lead to increased ammonium levels in the hindgut, contributing to struvite formation.
An alkaline pH environment is commonly found in horses with enteroliths. It’s unclear whether this is a result of diet or a predisposing condition made worse by diet.
Some horses appear genetically predisposed, especially when enteroliths develop in multiple related animals. More research is needed in this area.
Horses grazing on sandy soils are at higher risk due to chronic ingestion of sand, which may act as a base for enterolith formation.
In many cases, horses show no outward signs of enteroliths until they develop colic. Symptoms may include:
To help prevent the formation of enteroliths, consider the following management strategies:
Feed a 50:50 mix of lucerne and grass hay rather than a lucerne-heavy diet. Avoid feeding wheat bran, as its high phosphorus content may promote stone formation.
Increase daily exercise and grazing time to maintain healthy gut motility. Regular movement keeps bulk fibre moving through the intestines, reducing the chance of stone formation.
Check your horse’s manure periodically, especially if they graze on sandy soils. Small enteroliths may occasionally be expelled in droppings. Sandbuster assists passage of sand and indigestible materials through the intestines.
Keep paddocks, stables, and yards clear of foreign objects such as baling twine, plastic, wire, and stones that a horse might accidentally ingest.
Support digestive health with Clean Culture or UlcaBuf, which promote healthy hindgut pH, nutrient absorption, and digestive function. Their range of natural, coconut-based supplements can help reduce gut irritation and support overall intestinal wellbeing.
If one horse in a genetic line develops enteroliths, increase vigilance in related animals. Early intervention and dietary adjustments may help prevent future cases.
While not all horses will develop enteroliths, certain risk factors can dramatically increase the likelihood. A balanced diet, proper management, and digestive support supplements can help reduce your horse’s risk of developing these potentially dangerous intestinal stones. If your horse experiences recurrent colic or you suspect enteroliths, consult your veterinarian. Early diagnosis and management are key to preventing serious complications.
