What is an enterolith?

They are stone like balls that in the right circumstances can form in the horses intestinal tract. Entero means intestines and lith means stone. While smaller ones are often passed in the horses manure, larger ones are occasionally retained in the intestines and can eventually cause an obstruction. They are made of struvite which is a mucoid mix of ammonium, magnesium and phosphate.

How and why are they formed?

If the horse ingests a foreign body eg. pebble, wire, baling twine and it is not passed through in the normal manner, the horses body then seeks to protect itself. A mucoid matrix is laid down around the object to reduce its irritation to the lining of the gut. A similar situation would be that of an oyster making a pearl around a grain of sand. Over time the layers of mineral matrix buildup and the object becomes heavier and larger.

In some cases there are no obvious physical causes for the enterolith to develop.

There may be some genetic predisposition as genetically related individuals can develop the problem in clusters. More research needs to be done in this area before any definitive answer can be reached.

A diet with very high levels of lucerne hay or chaff is also strongly suspected of contributing to the problem. The high protein content also leads to higher amounts of ammonium in the gut.

An alkaline pH in the hindgut is often found in horses with enteroliths. More research needs to be done to know whether this is a result of the diet or whether it is pre existing and the diet aggravates the problem.

Horses grazing on very sandy soils may also be predisposed to enteroliths as the consumption of sand with the grass is a chronic intake that over time may lead to their development.

How do I know if my horse has enteroliths?

For many horses there are no obvious signs until they develop colic – smaller enteroliths lead to recurring episodes of colic. Larger enteroliths that are causing a bowel obstruction typically present as life threatening emergency cases. Radiographs of the horses abdomen will show them clearly as they are radio dense.

How can I try to prevent enteroliths from forming?

The following strategies are suggested:

• Feed grassy lucerne hay instead of high lucerne content hay. A 50:50 mix of grass and lucerne is ideal. It is not recommended to feed wheat bran in the diet as the high amount of phosphorus may help in the formation of the enteroliths.
• Increase exercise and grazing time to keep a large amount of bulk roughage moving through the gut on a regular basis.
• Check the manure on a regular basis for the presence of enteroliths especially if grazing on sandy soils.
• Keep paddocks and stables clean of any objects that may be accidentally ingested.
• Higher vigilance is also required if a genetically related horse develops enteroliths.