Gas colic is the most common form of colic in horses, accounting for roughly 80% of all colic cases. Most episodes resolve without surgery, but they can escalate quickly, so knowing how to respond matters. Relief comes from a combination of gentle movement, veterinary decompression when needed, and longer-term feeding changes that prevent gas from building up in the first place.
Why Gas Builds Up in the Hindgut
Horses are hindgut fermenters. They rely on billions of microbes in the cecum and large colon to break down plant fiber into short-chain fatty acids they can use for energy. That fermentation process naturally produces gas, which the horse normally passes without trouble. Problems start when the microbial balance shifts, usually because too much starch or sugar reaches the hindgut undigested.
When a horse eats a large grain meal, starch floods past the small intestine faster than it can be absorbed. In the hindgut, starch-loving bacteria (particularly Streptococcus species) multiply rapidly and produce excess lactic acid. That acid drops the pH, kills off the fiber-digesting bacteria the horse actually needs, and triggers a cascade: reduced microbial diversity, abnormal fermentation, and a surge of gas with nowhere to go. The colon distends, stretch receptors fire pain signals, and you see a horse in distress.
Common triggers include large grain meals, abrupt feed changes, lush spring pasture, and anything that disrupts the gut’s normal bacterial population. Even a sudden switch from pasture to stall life can slow intestinal motility and change water balance in the gut within 48 hours, compounding the problem.
Recognizing Gas Colic
A horse with trapped gas will typically paw at the ground, look or bite at its flanks, stretch out as if trying to urinate, lie down and get up repeatedly, or roll. Mild cases may show only restlessness and a loss of interest in food. More severe distension brings intense, unrelenting pain. The horse may sweat, refuse to stand, or thrash on the ground.
Check the heart rate. A normal resting rate for an adult horse is 28 to 44 beats per minute. A heart rate above 50 beats per minute, combined with pale or dark red gums, signals a serious problem that needs veterinary attention immediately. Gum color is one of the fastest indicators of circulation: pink and moist is normal, while pale, bright red, or purplish gums suggest compromised blood flow.
Immediate Steps You Can Take
If your horse is showing mild signs of gas discomfort, start with a calm walk. Walking stimulates gut motility, encourages gas to move through, and keeps the horse from rolling (which risks twisting the colon). Walk for up to one hour, but stop there. Walking for several hours exhausts the horse, worsens dehydration, and can actually slow gut motility rather than help it.
Remove all feed, including hay, until symptoms resolve. Leaving grain or rich forage available while the gut is already distended just adds fuel to the fermentation. Fresh water should stay accessible, though. Dehydration dries out gut contents and further slows passage. Horses moved from pasture to stalls show a significant drop in large intestinal motility within the first two days, partly because of shifts in water balance, so keeping water available is critical during any colic episode.
Some horse owners keep an anti-foaming agent on hand. Mineral oil, administered by a veterinarian through a stomach tube, can help break up certain types of gas bubbles. Do not attempt to drench a horse with oil orally on your own, as fluid can easily enter the lungs.
What the Veterinarian Does
When gas accumulates in the stomach or proximal intestine, a veterinarian passes a nasogastric tube through the nostril and into the stomach. Once the tube reaches the stomach, trapped gas escapes immediately, often with a rush of foul-smelling air. The vet then checks for fluid reflux by creating a siphon with warm water. If large volumes of fluid come back, it means the intestine downstream is obstructed, and the situation is more serious than simple gas.
This stomach tube serves double duty: it relieves pressure and prevents gastric rupture, which is fatal. In horses with ongoing reflux, the tube stays in place, secured to the halter with a one-way valve, and the vet rechecks every couple of hours. For cases that respond well, the vet may administer fluids and electrolytes directly through the tube to rehydrate gut contents and encourage passage.
Your vet will also likely administer a pain-relieving anti-inflammatory. If the horse responds to this combination of decompression, pain management, and walking within an hour or two, the prognosis is excellent. Gas colic that doesn’t respond to treatment, or that comes with a persistently high heart rate and abdominal distension, may indicate a twist or displacement requiring surgery.
Feeding Changes That Prevent Gas
Prevention is almost entirely about how and what you feed. The horse’s digestive system evolved for near-constant grazing on fibrous forage, roughly 16 hours a day. Large, infrequent meals of concentrated grain are the single biggest dietary risk factor for gas colic.
Keep forage as the foundation of the diet. Horses need a minimum of 1% of their body weight in hay or pasture forage daily, so at least 10 pounds for a 1,000-pound horse. Ideally, forage intake should be as high as practical. Long-stem hay slows the rate of passage through the gut and gives hindgut microbes the steady supply of fiber they’re designed to process.
If your horse needs grain, limit the amount per meal. Research from Oklahoma State University suggests that more than about 2 grams of starch per pound of body weight overwhelms the small intestine’s capacity and sends undigested starch into the hindgut, where it ferments into gas and acid. In practical terms, that means a 1,000-pound horse should get no more than about 5 to 6 pounds of a typical grain mix per day, split into at least two feedings. Some nutritionists recommend even smaller meals of 0.2 to 0.4% of body weight at a time, which works out to 2 to 4 pounds per feeding for a 1,000-pound horse.
Any diet change, whether it’s a new hay source, a different grain, or a shift from pasture to stall, should happen gradually over 7 to 14 days. Abrupt changes don’t give the hindgut bacteria time to adjust, and the microbial disruption that follows is a well-documented colic trigger.
Hydration and Turnout
Horses on pasture get a significant portion of their water from fresh grass, which is roughly 80% moisture. When a horse moves to a stall and dry hay, its drinking water intake nearly triples to compensate, but total gut hydration still drops. One study found that fecal dry matter content jumped from about 19% on pasture to 27% after stabling, while large colon motility decreased significantly in the first five days. Drier, slower-moving gut contents create the conditions for both impaction and gas accumulation.
Providing clean water at all times is the simplest intervention. In cold weather, horses drink more when water is lukewarm. Adding loose salt to the feed (or providing a salt block) encourages drinking. Soaking hay or feeding beet pulp mixed with water are other ways to sneak extra moisture into the diet. Turnout and free movement also support motility, so horses with access to pasture or paddock time have a natural advantage over those standing in stalls for long stretches.
Probiotics and Gut Support
Probiotic supplements aim to reinforce the beneficial microbial population in the hindgut. The most commonly used strains in equine products include Lactobacillus (which can inhibit harmful bacteria and reduce risk factors for hindgut acidosis), Bifidobacterium (which supports vitamin production and mineral absorption), and Saccharomyces yeast strains (which help maintain the intestinal lining and may protect against leaky gut).
These supplements are most useful during high-risk periods: after antibiotic treatment, during diet transitions, around travel or competition, or for horses with a history of recurrent gas colic. They’re a supportive measure, not a substitute for proper feeding management. The evidence for probiotics in horses is growing but less robust than in human medicine, so think of them as one tool in a broader prevention strategy rather than a standalone fix.