Colic in horses has no single cause. It’s a broad term for abdominal pain, and dozens of different problems can trigger it, from something as simple as a change in hay to life-threatening intestinal twists. Roughly 4 out of every 100 horses experience a colic episode each year, and about 11% of those cases are fatal. Understanding what sets it off is the best way to reduce your horse’s risk.
The Horse’s Gut Is Built for Trouble
Horses have an unusually long, complex digestive tract that ferments forage in the hindgut rather than the stomach. Several spots along this path are natural bottlenecks. The pelvic flexure, where the large colon makes a sharp turn and dramatically narrows, is the most common site for impactions. The junction between the right dorsal colon and the transverse colon is another pinch point, as is the base and body of the cecum (the large fermentation chamber at the start of the hindgut).
The large colon itself is mostly free-floating inside the abdomen, held loosely in place rather than firmly anchored. This gives it room to shift, twist, or even flip over on itself. In left dorsal displacement, the colon migrates over a ligament between the spleen and left kidney, getting trapped in a natural cleft. In right displacement, the colon swings laterally around the base of the cecum and presses against the right body wall. These displacements can block the flow of digesta and cause severe pain.
Diet Is the Most Common Trigger
What a horse eats, how much, and how quickly it changes all directly affect colic risk. Grain and concentrate feeds are the biggest dietary culprits. Horses fed 2.5 to 5 kilograms of concentrate per day have nearly five times the colic risk compared to horses fed no grain. Above 5 kilograms per day, the risk jumps to more than six times higher. Large starch loads overwhelm the small intestine’s ability to digest them, sending undigested carbohydrates into the hindgut where they cause rapid fermentation, gas buildup, and shifts in the microbial population.
Switching feeds abruptly is another well-known cause. The microbial community in the hindgut is adapted to whatever the horse has been eating. When you suddenly introduce a new type of hay or a different grain, those microbes can’t adjust fast enough, leading to gas, irritation, and sometimes impaction. Any feed change, including a new batch of hay, should be mixed gradually with the old feed over 10 to 14 days.
Horses that don’t get enough forage are also at higher risk. Roughage keeps the gut moving and provides the bulk needed for healthy motility. Without it, the digestive tract slows down and material can compact in those natural bottleneck areas.
Dehydration and Cold Weather
An average adult horse moves 90 to 135 liters of water back and forth across the colon walls every day. That water keeps the food material soft and moving. When a horse doesn’t drink enough, the colon reabsorbs more water from the digesta, leaving it dry and packed. This is the basic mechanism behind impaction colic, and it’s the reason colic spikes during winter months.
Cold weather creates a cause-and-effect relationship with impactions. Horses naturally drink less when water sources are near freezing. One study found that horses offered warm water in cold climates drank 40% more than horses given cold water. Reduced turnover from winter stall confinement compounds the problem: less movement means less gut motility.
Sand Ingestion
Horses that live or graze in sandy regions, particularly in states like Florida, California, and Arizona, can accumulate sand in the large colon over time. They pick it up by eating hay off the ground, grazing short pastures down to the dirt, or simply scavenging when forage is scarce. Young horses and those with indiscriminate eating habits sometimes consume sand voluntarily.
Sand is heavy and settles to the bottom of the colon, irritating the lining and eventually forming a mass large enough to block the passage of food. Horses with insufficient pasture or too little roughage in their diets are especially prone to accumulating it. Feeding from elevated hay nets or feeders rather than off the ground significantly reduces the risk.
Parasites
Internal parasites remain a meaningful cause of colic, particularly tapeworms. When large numbers of tapeworms attach to the walls of the cecum and the end of the small intestine, they cause physical obstruction and damage the intestinal lining. That damage can range from mild inflammation to deep, overlapping ulcers at the attachment sites. The ulceration triggers abnormal contractions and intestinal spasms, which can lead to ileal impactions or even intussusception, where one segment of intestine telescopes into another.
Strongyle worms, especially the large strongyle species, can damage blood vessels supplying the intestine, reducing blood flow and causing tissue death in sections of the gut wall. A consistent, veterinarian-guided deworming program based on fecal egg counts is the standard approach to managing parasite-related colic risk.
Pain Medications That Backfire
Non-steroidal anti-inflammatory drugs (commonly called “bute” and similar pain relievers) are widely used in horses, but they can damage the lining of the large colon when given at high doses or for extended periods. The resulting condition, right dorsal colitis, causes the colon wall to ulcerate and leak protein. Horses develop recurring colic, weight loss, soft feces, swelling under the belly, and poor appetite.
Some horses are inherently more sensitive to these drugs, and toxicity can develop even at recommended doses. Signs may appear days to weeks after treatment begins, making it easy to miss the connection. This is one reason pain medications in horses should always be used at the lowest effective dose for the shortest necessary time.
Age-Related Risks
Older horses face a specific and serious form of colic caused by fatty tumors called strangulating lipomas. These are benign growths on stalks of fatty tissue that hang from the mesentery, the membrane supporting the intestines. Over time, a stalk can wrap around a loop of small intestine and cut off its blood supply entirely. The average age at presentation is 14 to 19 years.
This condition was once blamed on obesity, but current evidence points to hormonal and metabolic changes in aging horses as the primary driver. Conditions like insulin resistance and Cushing’s disease alter fat deposition patterns and appear to increase the incidence, particularly in older geldings. Strangulating lipomas almost always require emergency surgery.
Stress and Management Changes
Stress is a less tangible but well-recognized colic trigger. Trailering, competition, changes in routine, new herd dynamics, and stall confinement after turnout can all disrupt gut motility. Horses are creatures of habit, and their digestive systems respond to environmental stress with changes in motility, water intake, and eating patterns. Even something as simple as a change in feeding schedule can be enough to slow gut transit and set the stage for impaction or gas colic.
Horses that shift abruptly from regular exercise to stall rest, such as after an injury, are at elevated risk. Consistent daily movement, even light hand-walking, helps keep the intestines active and reduces the chance of food material stalling in the colon.