Thoroughbred colt Berkshire’s (pictured right) uncharacteristic performance alerted trainer Paul Cole to a possible problem.

“Four weeks before the Greenham Stakes [April 2014], he worked the best we’ve ever seen,” says Oliver, Paul’s son and assistant trainer. “But a fortnight later he seemed a bit hesitant and he ran badly in the race itself. He was gastroscoped and ulcers were found, so when he then became colicky we put it down to that.”

The colic worsened, however, and when vets at Donnington Grove Surgery operated, they discovered an enterolith in Berkshire’s small colon.

“We didn’t know the precise diagnosis until we opened him up,” says treating vet Alastair Welch. “The grapefruit-sized enterolith was large enough to cause a blockage in an area where the gut narrows.”

Surgery to remove the enterolith was successful and Berkshire later returned to his winning ways. But what creates such a blockage? In this case the stone was thought to have formed around a small piece of rug.

Foreign bodies

“Enteroliths, also known as ‘stones’ and ‘calculi’, are mineralised concretions that form within the intestines,” explains Tim Mair MRCVS from Bell Equine.

“Made of struvite crystals (magnesium ammonium phosphate), they usually form around a nidus (foreign body) such as a natural stone or metal object that the horse has swallowed. Other foreign objects, such as fragments of lead ropes, rugs and electric fencing can also be eaten and become mineralised, forming an enterolith.

“Enteroliths often sit in the large intestine for many months or years, where they slowly enlarge as more mineral is deposited on their surface. Small enteroliths may pass out in the droppings, but if an enterolith grows to a large size, it can become lodged in the intestines and cause an obstruction resulting in colic.

“The colic can be acute and severe, or mild, intermittent and recurrent – depending on the location of the enterolith. A change in attitude and the passage of scant, mucus-covered faeces may also be observed.

“Enteroliths in the large colon usually cause mild signs of intestinal discomfort. However, if they migrate into the narrower transverse or small colons, signs of acute and complete obstruction develop, with severe pain and progressive abdominal distention. Immediate surgery is required to remove the enterolith(s) and prevent intestinal rupture.”

Spot the ball

“Diagnosis is often only made at surgery, but in a small number of cases an enterolith may be felt by a rectal examination,” says Tim. “In geographical areas where enteroliths are common, X-rays of the abdomen can also be used for diagnosis.

“Surgical removal is usually undertaken with the horse lying on his back under general anaesthesia. An incision is made along the middle of the belly to allow access to the intestines.

“Depending on its location in the long intestinal tract (which averages nearly 100 feet in length), it may be necessary to manipulate and move the enterolith into a region of the intestine that can be more easily accessed. It can then be removed by incising and opening the wall of the intestine.

“The prognosis is generally good, provided that the enterolith hasn’t caused too much damage to the intestine wall.”

Ref: Horse & Hound; 4 June 2015