Intestinal stones in horses: A cause of colic!

Intestinal stones can occur in equids (horses, mules, ponies, and zebras) at any age. Intestinal stones are also referred to as enterolithiasis, intestinal calculi, concretions and bezoars (Figure 1). Years ago, it was common practice to value the intestinal stones (in Persia people thought the stones would ward off disease) and often neighbors would come by to rub the intestinal stone for ...Intestinal stones can occur in equids (horses, mules, ponies, and zebras) at any age. Intestinal stones are also referred to as enterolithiasis, intestinal calculi, concretions and bezoars (Figure 1). Years ago, it was common practice to value the intestinal stones (in Persia people thought the stones would ward off disease) and often neighbors would come by to rub the intestinal stone for ...

Story originally posted by: Michael Lowder, DVM, MSUniv. of GA School of Veterinary Medicine

Intestinal stones can occur in equids (horses, mules, ponies, and zebras) at any age. Intestinal stones are also referred to as enterolithiasis, intestinal calculi, concretions and bezoars (Figure 1). Years ago, it was common practice to value the intestinal stones (in Persia people thought the stones would ward off disease) and often neighbors would come by to rub the intestinal stone for good luck. They are first reported in the literature in millers horses (horses that were used to work in mills), but can be found today in any breed of horse.

The incidence of intestinal stones appears to be increasing today when compared to the number that were reported in the late 1800’s and early 1900’s. This could be due to the fact that more horses go to surgery today than ever before (thus, the chance for detecting one is higher), and more horses today are fed a diet that might aid in the formation of intestinal stones. Intestinal stones are reported more commonly in certain countries (more are reported in the USA now than in Europe) and within specific geographic locations (more often in the southwestern part of the USA and Tahiti). Within the United States, more are reported in California than any other state. There is no predilection for sex with the disease, but there does appear to be a breed predilection with Arabians being more commonly affected.

Why are Arabians more commonly affected than other horses? We’ll see. Intestinal stones can be either smooth or rough, and may occur singly or in groups. How does a surgeon tell if there are more than one intestinal stone in the bowel when performing surgery? The appearance of the stone is a dead give away. If the intestinal stones are round then there is only one but if the intestinal stones have any flat sides then there are at least two (the flat side occurs as the stones rub against one another) and if tetrahedral in shape, then there are at least three intestinal stones. What are the intestinal stones composed of? As mentioned above, they are a mixture of accumulated minerals (ammonium magnesium phosphate) with some type of foreign nidus at the center (metal, coins, teeth, pebbles, cloth, hair, etc). They can weigh as much as 12 kilograms but often are 0.5 to 1.0 kilograms.

Does your horse have intestinal stones? What do you look for? Oftentimes affected horses show clinical signs consistent with that of colic. They can include, but are not limited, to persistent or recurrent low-grade abdominal pain (lying down looking at their belly), partial or complete anorexia (they’ll stop eating their best treats) and frequently have an absence of defecation. These symptoms can occur over a few days to weeks and even years in some cases. How can this be? How can a horse have intermittent abdominal pain over a few days, weeks or even years? Easily, as the intestinal stone oftentimes is located just proximal to the transverse colon (a small colon leading from the large dorsal right colon) in the larger right dorsal colon and functions as a ball valve to the opening of the transverse (descending) colon. This may periodically obstruct the passage of feed through the bowel and causing the abdominal pain. Frequently, there will be a decrease in the intestinal motility with a decrease or absents of gut sounds (borborygmi) in the affect horse.

The temperature, heart and respiratory rate will often be normal with the heart and respiratory rate increasing as the level of discomfort increases. Tachycardia (an increase in heart rate) is often the first clinical sign that can be detected but usually only the attentive owner will notice. Do intestinal stones always require surgery? Not always as some are passed through the intestinal tract and are often found by owners picking their horse’s stall. However, these are not the ones causing the problems for most owners.

So what factors are associated with the formation of intestinal stones? The exact etiology of intestinal stone formation is unknown, but we do have our thoughts. They include a nidus, diet, intestinal luminal pH, soil type, age, and maybe breed. A nidus is found in most every intestinal stone. It appears that some type of foreign body must be present to act as a core for deposition of the minerals. Silicon dioxide appears to be the most common nidus as it is a normal part of most fieldstones; thus, easily ingested. Thus, the reason why millers horses frequently got intestinal stones was due to the grit from the millstones ending up in the millpond (the source of the horse’s drinking water).

Diet is likely the most common thing reported to be associated with intestinal stones as most horses with intestinal stones are on a diet of alfalfa hay or wheat bran. As alfalfa hay is rich in minerals and wheat bran is high in protein, phosphorus and magnesium. It has been reported that changing the diet can reduce the probability of having intestinal stones form in one’s horses.

Intestinal pH (an increase) has been cited as a possible cause of intestinal stones but data is lacking to say for sure. To combat this some owners have fed their horses decreased amounts of hay and fed more grain (this decreases the pH of the colonic contents). Others have added vinegar to the diet to decrease the pH, but this has not been shown helpful.

Intestinal stones have been reported more often in horses between 5 and 9 years of age but can occur in any aged horse. Arabians and part-Arabians are been stated to have a higher incidence rate of intestinal stones than other breeds of horses. This may be due to the fact they may have some different intestinal enzymes or function. Soil type does appear to play a roll as more horses are reported to have intestinal stones that live on a sandy soil than horses that do not.

When the veterinarian arrives, the horse will often not be exhibiting the clinical signs that the owner notice when they called the veterinarian out (as the intestinal stone moves away from the opening of the transverse colon). Diagnosis is often made by history; rectal examination (the intestinal stones can not be palpated), abdominal radiographs or an exploratory surgery may be necessary to confirm the diagnosis. Surgery is the only effective treatment known to date.

Surgery is best done before the stone damages the bowel, which could lead to eventual bowel rupture and death. If you have any questions about this article please email me at health@HorseCity.com and I will try to answer them.