Large Intestinal Colic in Horses: Nutritional Considerations

Colic of the large intestine can result from gas or fluid distension, obstruction (impaction or enteroliths), or twisting of the gut (as in large intestinal volvulus or displacement of the large colon). The clinical signs of large intestinal colic are moderately elevated heart rate (60-80 beats per minute or more, whereas normal is 28-40 beats per minute) and mild to moderate pain that is often intermittent. Usually there is no gastric reflux when a nasogastric tube is passed into the stomach.

Impactions are dry masses of feed material that lodge in the intestine and occlude it. The intestine can spasm which further squeezes water from the impaction and this produces more pain. Fluid or gas will accumulate ahead of the impaction and distend the gut. One of the most common areas for impaction of the large intestine is the pelvic flexure. The pelvic flexure is a 180° turn between the left ventral and the left dorsal colon; it is normally found in the lower left of the horse’s abdomen and is easily palpated rectally. This hairpin turn and narrowing of the large intestine predispose it for impaction, but impactions can occur anywhere in the large intestine. Fortunately, pelvic flexure impactions usually respond well to medical management, although affected horses will sometimes need to be hospitalized to receive intravenous fluids in order to remain hydrated.

Enteroliths are concretions of mineral that usually form around a foreign body such as baling twine or, fencing debris. As an enterolith enlarges, it can act as a ball valve in the large intestine, causing a build-up of fluid and gas ahead of it. The enterolith can slip back into a position where the gut is not occluded, and colic can resolve with routine therapy. This makes enteroliths difficult to diagnose because they are difficult to palpate rectally, even when they cause colic. Depending on the size of the horse and location of the enterolith, the blockage can sometimes be diagnosed using abdominal radiography (X-ray). Enteroliths are most often diagnosed during exploratory surgery. Several studies have shown that enteroliths are more common in California, in Arabian horses, and in horses over 4 years of age.

Enteroliths are composed of magnesium, calcium, and variable amounts of other minerals. Diets high in alfalfa are a recognized risk factor for enteroliths. It is believed that the combination of high dietary calcium, magnesium, and elevated concentrations of ammonia in the gut when protein is digested all contribute to enterolith formation. The only practical way to prevent enteroliths is to restrict or eliminate alfalfa from the diet.

The vast majority of colic episodes in horses respond well with passage of a nasogastric tube to relieve gas or fluid accumulation, administration of drugs for pain (flunixin or butorphanol, for instance), and potentially laxatives (mineral oil). Colicky horses that remain painful despite aggressive therapy require exploratory surgery to diagnose and correct the cause of abdominal pain. One of the most severely painful and potentially devastating large intestinal problems is large colon volvulus (twist). These are more common in postpartum mares but can occur in any horse. It is important that large intestinal volvulus is recognized within a few hours of onset so the organ can be surgically untwisted and recover.

The large colon can displace, or move from its normal position in the abdomen, and not necessarily twist. Pain still occurs due to tension on the gut or accumulation of gas. Large colon displacements tend to have a favorable surgical prognosis. An example is left dorsal displacement or nephrosplenic entrapment, in which the left colon rises up over the nephrosplenic ligament (a ligament between the spleen and left kidney) and becomes entrapped. Many cases will need surgical correction, but some resolve with medical therapy to shrink the spleen or by rolling the horse under general anesthesia.

Horses that have had a colic episode that responded well to routine medical therapy are usually best managed with an additional 2-3 days of dietary modification. Whenever colic occurs, it is useful to review if anything has changed in the horse’s life that may have led to colic, such as cold weather that may have decreased water intake or a change in hay or concentrate feeding (different source or an increased amount). Fasting for 12-24 hours is a good practice to decrease the amount of feed material in the horse’s gut and to allow the gut to rest. Horses can be offered small, frequent drinks of water to maintain hydration. Most veterinarians recommend some period of feed restriction and decreased concentrate feeding for 1-2 days after a colic episode. Short hand-grazing sessions (5-15 minutes) are excellent to allow some feed intake, and walking generally promotes movement of feed through the intestine.  Many veterinarians recommend that the horse receive only 50% of its normal concentrate diet for the first day after colic. If hay is restricted, it can be sprinkled throughout the horse’s stall to stimulate grazing and prolong the horses’ eating time.

Horses that have had surgery are more complicated to nourish; how soon the horse is fed and what the horse eats depends on the extent of surgery. Healthy adult horses can tolerate many days of feed deprivation as long as they are kept hydrated. Most surgeons will completely fast the horse for 2 days before a gradual return to feed if a bypass, resection, or anastomosis was performed. It is important to avoid bulk in the intestine for several days to ease strain on the intestinal repair site and to allow the best chance for a strong and healthy return to gut function. If no gut was removed and the intestine appeared fairly healthy, then the horse may be fed as for a routine colic. Regardless, it is important to not rush the horse back onto feed so maximal healing occurs. Access to fresh grass is better than hay to avoid excessive roughage.

Bran mashes are commonly recommended as a preventive or treatment for large intestinal impactions. However, research has shown that feeding bran mash does not increase the water content of manure and provides no laxative effect. Bran mash has little potential to do any harm unless there is a deficiency of calcium in the diet, which creates an excessive dietary phosphorus-to-calcium ratio. Perhaps the best we achieve with feeding bran mashes is to increase the horse’s water intake and keep colicky horses eating.