Colic in horses is caused by a wide range of digestive problems, from simple gas buildup to life-threatening twists in the intestine. It affects roughly 4 out of every 100 horses per year, making it one of the most common emergencies in equine medicine. The underlying causes fall into several categories: gas distension, impaction, intestinal displacement or twisting, inflammation, ulceration, and parasites. In many cases, no specific cause is ever identified.
Why Horses Are Built for Colic
A horse’s digestive tract is 50 to 70 feet long, and large sections of it aren’t anchored to anything. Some portions attach to the body wall by only small strips of tissue, which means loops of intestine can shift into abnormal positions, fold over themselves, or become trapped. This is a fundamental design vulnerability. Unlike a dog or a human, a horse also cannot vomit, so anything causing a blockage or gas buildup has no easy escape route. The pressure just builds.
The combination of a massive, loosely suspended gut and a one-way digestive system makes horses uniquely prone to abdominal pain that other species simply shake off.
Gas and Impaction: The Most Common Causes
Flatulent colic happens when excessive gas accumulates in the intestines, stretching the gut wall and causing pain. This can result from sudden dietary changes, lush spring pasture, or feeds that ferment rapidly in the hindgut. Most gas colic episodes resolve on their own or with minimal veterinary intervention.
Impaction colic occurs when a mass of dry feed material, usually partially digested hay, lodges in a narrow section of the intestine. The pelvic flexure, a hairpin turn in the large colon, is a frequent trouble spot. Dehydration is the single biggest contributor. A 1,000-pound horse needs roughly 10 gallons of water per day under normal conditions, and intake drops significantly in cold weather when water sources are frigid. Without enough water, gut contents dry out, slow down, and compact.
Winter is peak season for impaction colic. Horses drink less, move less, and eat more dry hay. Any combination of reduced water intake and decreased exercise raises the risk considerably.
Grain Overload and Feeding Mistakes
Diet is one of the most controllable risk factors. A study published in the Journal of the American Veterinary Medical Association found that horses fed more than 6 pounds of oats per day were nearly six times more likely to develop colic than horses fed 6 pounds or less. That’s a striking increase from a seemingly modest dietary difference.
The issue isn’t just quantity. Sudden changes in feed type or schedule, irregular meal timing, and large single meals of concentrate all disrupt the microbial balance in the hindgut. Horses evolved to graze continuously on fibrous forage. When starch-heavy grain arrives in large boluses, it can overwhelm the small intestine’s capacity to absorb it, dumping undigested starch into the cecum and colon. The result is rapid fermentation, gas production, acidosis, and pain.
Sand Accumulation
Horses that eat off sandy ground or graze on sparse, sandy pastures gradually ingest sand with every meal. That sand settles in the lowest portions of the large colon, particularly the ventral colon, pelvic flexure, and transverse colon. Over weeks or months, enough can accumulate to physically block the passage of feed material and irritate the intestinal lining.
Sand colic is regional. It’s common in the American Southwest, parts of Florida, and anywhere with sandy soil. Horses with insufficient pasture or too little roughage in their diets are more prone to ingesting sand while scavenging for food. A simple at-home screening involves dissolving a few fecal balls in water in a bucket or rectal glove and watching for sand settling at the bottom.
Enteroliths: Mineral Stones in the Gut
Enteroliths are mineral stones that form inside the large colon over months or years, eventually growing large enough to block the intestinal passage. They’re composed primarily of struvite, a crystal made of magnesium, phosphorus, and nitrogen.
Diet plays a central role. Horses fed predominantly alfalfa hay have significantly higher concentrations of magnesium, calcium, and phosphorus in their colon contents, along with a more alkaline pH, all conditions that favor stone formation. Alfalfa grown in California is particularly high in magnesium, and enterolith cases cluster heavily in that state. Mixing grass hay into an alfalfa-heavy diet and providing access to pasture grazing can help reduce the risk.
Parasites and Tapeworms
Internal parasites have been causing colic in horses for as long as both have existed. While modern deworming programs have reduced the worst parasite-related emergencies, tapeworms remain a significant and underrecognized cause.
The equine tapeworm attaches to the intestinal lining right at the junction between the small intestine and the cecum. This attachment causes local inflammation and tissue damage. Research has found a dramatic association between tapeworm infection and ileal impaction colic: infected horses had odds ratios ranging from 26 to 44 times higher for developing this specific type of blockage compared to uninfected horses. In one study, horses that had received a dewormer effective against tapeworms within the previous three months were three times less likely to be admitted for ileal impaction.
Large strongyles, once the most feared equine parasite, cause colic by migrating through the blood vessels supplying the intestine. They can damage arterial walls and reduce blood flow to sections of the gut. Routine deworming has made this less common, but it still occurs in horses with poor parasite management.
Displacement, Torsion, and Strangulation
These are the emergencies. A displaced colon has shifted out of its normal position, sometimes trapping gas and fluid behind it. A torsion means the intestine has twisted on itself. A strangulating obstruction cuts off both the intestinal passage and the blood supply to that segment of gut, causing tissue to die within hours.
Strangulating lesions are the most dangerous form of colic. They cause severe, unrelenting pain and require emergency surgery. Only about 1.4% of all colic events lead to surgical intervention, but strangulation accounts for a disproportionate share of colic deaths. The large colon’s loose attachments make displacement and volvulus (a full twist) possible in ways that wouldn’t happen in a more securely anchored digestive system.
Small intestinal strangulation can also occur when a loop of bowel passes through a natural or abnormal opening in the mesentery (the tissue that suspends the intestines) or becomes caught in an inguinal ring, particularly in stallions.
Inflammation, Ulceration, and Medication Effects
Enteritis and colitis, inflammation of the small or large intestine, cause colic along with diarrhea, fever, and rapid dehydration. Infectious causes include salmonella and clostridial bacteria. Colitis can progress quickly and become life-threatening.
Gastric ulcers are extremely common in horses, especially those in regular training or competition. Ulceration of the stomach lining and sometimes the intestinal lining causes low-grade, recurring abdominal discomfort. Horses may show subtle signs: poor appetite, weight loss, sensitivity when girthed, or mild colic episodes after eating.
Anti-inflammatory medications commonly used in equine practice can themselves cause digestive damage. When given at high doses or for extended periods, these drugs can erode the lining of the right dorsal colon, a condition called right dorsal colitis. Some individual horses are unusually sensitive and develop problems even at standard doses. Symptoms can appear days to weeks after treatment begins, making the connection easy to miss.
Stress, Management, and Lifestyle Factors
Beyond specific diseases, the way a horse lives has a profound effect on colic risk. Stall confinement reduces gut motility. Horses that stand in a stall all day simply don’t move feed through their system as efficiently as horses with turnout. Changes in routine, such as travel, new housing, or a shift in the feeding schedule, are well-documented triggers.
Stress itself appears to alter gut function. Horses undergoing transport, competition, or social disruption (a new herd, loss of a companion) are at elevated risk in the days that follow. The gut’s nervous system is highly responsive to stress hormones, which can slow motility, reduce blood flow to the intestinal lining, and shift the microbial population.
The practical takeaway is that the most preventable causes of colic revolve around management: consistent feeding schedules, gradual diet transitions, adequate water access (warmed in winter if needed), regular turnout, appropriate deworming based on fecal egg counts, and avoiding excessive grain. None of these eliminate the risk entirely, because some colic has no identifiable cause at all, but they meaningfully reduce it.