The term “colic” fits all varieties of abdominal distress our horses experience. The causes of colic in horses range from the passing discomfort of excessive gas to life-threatening intestinal torsions. The majority of colics in horses are mild, but they’re still troublesome, causing horses to pace, paw and roll while their caretakers fret over their discomfort. In these cases, the digestive system rights itself, given a little time or minimal medical attention.

Major intestinal disruptions, including blockages, twists and ruptures, are usually fatal unless surgery to remove or repair the diseased area of gut succeeds. Each year, hundreds of horses die on the operating table or shortly after, due to the disease itself or to complications from it.

Researchers haven’t found a magic serum to guarantee your horse a colic-free life, but their increased understanding of equine digestion has allowed them to identify many of the conditions that predispose horses to colic. Using this information as the basis for preventive action, horse owners can take control of the stabling, dietary and environmental conditions that influence equine digestion for better or worse. By adopting consistent, rational management practices and maintaining horses according to Nature’s operating manual, you can minimize your horse’s risks of digestive distress.

Feeding to Prevent Colic

Horses are designed to graze on an unvarying diet of fibrous, low-energy forages for 12 to 20 hours per day. Unfortunately, domesticated living usually challenges the horse’s sensitive digestive tract with feedstuffs, feeding schedules and ration portions that are far outside the norm of the natural plan. One of the primary reasons horses colic is the disparity between what the digestive equipment is intended to process and what it actually gets. Start your anti-colic campaign by evaluating and, if necessary, revamping your feeding practices.

• Feed your horse only what he needs. When it comes to maintaining digestive health, the best thing your horse can put in his mouth is grass, a high-fiber, low-carbohydrate feed containing eight to 10 percent protein. The second-best horse feed is grass in its dried, stored form, otherwise called hay. The bulk delivered by a fibrous grass/hay diet is a key weapon in fighting the colic wars because consistent gut fill maintains a continuous level of digestive activity, free of feast-or-famine stresses. Additionally, horses usually chew hay twice as long as grain. The more they chew, the more saliva is generated and mixed in, which helps buffer the stomach against acids.

This near-perfect grass/hay diet may not provide sufficient energy and other nutrients for the daily demands placed on some horses. Enter concentrates, feeds that boost one or more of the tissue-building and fuel-supplying dietary components: protein, energy and fat. The grain mixes commonly fed to horses usually include some combination of corn, oats and barley in pelleted or sweet-feed form and coated with molasses to improve palatability. The simple carbohydrates provided by concentrates–sugars, starch and soluble fiber–are good horse fuel in moderation. But an excess of starches in a horse’s ration can upset the gut’s delicate bacterial balance.

The digestion and absorption of modest amounts of starch occur in the small intestine, then the ingesta enters the horse’s cecum and large intestine where fibrous particles are broken down. If a glut of simple carbohydrates overwhelms the starch-converting enzymes available in the small intestine, the remaining undigested carbohydrates pass into the cecum and large intestine. Some microbes there prosper on the starch, producing a high level of lactic acid as they break it down. This lactic acid kills key microbial fiber digesters in the hindgut. The resulting by-product inflames the gut wall and opens the way for absorption of toxins into the bloodstream.

“Normally, during fiber fermentation, these microbes produce volatile fatty acid, which is good,” says Stephen Duren, PhD, of the equine nutrition and conditioning consulting firm Kentucky Equine Research, Inc. “In this case, the bacteria are killed by their own end product.”

To reduce the risk of intestinal distress, review your horse’s diet and feeding schedule, particularly his grain intake. Do you feed him grain because his work demands it or simply because all the other horses in the barn get grain? If you have a few companion ponies or pensioners among a barn full of performance horses, for example, a handful of grain will keep the nonworkers content at mealtimes without placing undue strain on their digestion.

What is a justifiable reason for including grain in a ration, then? “Horses are made to eat grass and hay, and they supplement their food with a variety of plant material,” says veterinarian Joyce Harman, DVM, MRCVS, of the Harmany Equine Clinic in Washington, Virginia. “The reason for adding grain is to make up the calorie difference. The goal is to feed to maintain good body weight.” Depending upon the horse’s age, level of activity, lactation status and innate metabolic rate, the additional grain required to maintain an ideal weight may range anywhere from one to possibly 15 pounds a day.

The generally accepted maximum for concentrates in a horse’s diet is no more than half the total amount–by weight–of the ration fed. “If you’ve got a 1,000-pound horse consuming 30 pounds of feed, and he’s eating 20 pounds of grain, then you’re looking at a colic risk,” says nutritionist Sarah Ralston, VMD, PhD, of New Jersey’s Rutgers University.

When you feed grain, offer it in two- to four-pound mini-meals spaced evenly throughout the day. Mixing the grain with moistened, chopped hay or grass also prolongs the horse’s intake and modulates the amount of starch entering the gut at any one time. Finally, oats are the safest of all the common horse grains because they are highest in fiber and contain the most digestible form of starch, making them the least likely to trigger a starch overdose.

• Stick with your feeding program. Frequent or sudden changes in your horse’s diet are enough to push him into the colic zone, regardless of what the actual dietary ingredients are. It’s that tricky microbial balance again. “If the microbes in the intestines get used to a food that isn’t fed in an oversupply, the horse can adapt quite well to his diet,” says Nathaniel White II, DVM, of Marion duPont Scott Equine Medical Center in Leesburg, Virginia. “The problem comes if you change the type of food or the amount you feed. Then the microbes are unbalanced and upset.”

Sometimes the dietary disruption is purely accidental, as in the case when an owner runs out of his usual hay or grain and feeds a replacement that is quite different. Or the horse may be moved to a stable or region of the country where entirely unaccustomed feedstuffs are used. “Grains have different amounts of starch, protein and molasses–different nutrient profiles,” says Duren. “The digestive system needs time to adjust to those different levels.”

Horses adapt to new grains and hay all the time, and some can accept major and abrupt changes without any ill effects. But to be on the safe side, convert your horse to different rations gradually over 7 to 10 days. Reductions in ration size or nutrient levels can be made relatively rapidly, in a week or less. But when you’re bumping horses up to higher-powered diets involving more carbohydrates, fat and/or protein, take at least 10 days of incremental increases to give the intestinal bacteria time to acclimate to the new diet.

When upping a horse’s ration, suggests Kathleen Crandell, PhD, of Kentucky Equine Research, Inc., begin by mixing one-quarter portion of the new grain with three-quarters of the old grain for two days. Continue to increase the new grain in the ration by a quarter every two to three days until the new feed completely replaces the old grain. Crandell recommends a similar stepwise process when switching hay. Horses who are accustomed to eating low-protein, moderate quality grass hay and are switched suddenly to a legume, such as alfalfa, often experience some degree of digestive disturbance.

• With grain, think small and often. The human dietary schedule of three meals a day–or even fewer for those on the run–is a ritual that fits our carnivorous needs. You gobble down a substantial meal, which lingers in your rather large stomach, and digest it over the course of the day.

Horses, on the other hand, are continual foraging machines. When left on pasture and to their own devices, horses pick and choose their mouthfuls here and mouthfuls there for as many as 20 hours a day. These bite-size portions remain in the stomach for less than two hours and in the small intestine for about an hour, then spend from several hours to a couple days getting the full digestive treatment in the large intestine. In all, an average horse ration takes anywhere from 12 to 36 hours to run its course through the gut. Coarse or dense fibers may spend as long as seven days undergoing the digestive efforts of the intestinal microbes.

Unfortunately, our meat-eating mealtime schedule can wreak havoc on our horses’ vegetarian setup. We’ll dump a few scoops of grain in the feed tub a couple times a day, not realizing that these feeding practices put a real strain on horses’ digestive equipment. “The horse’s stomach has only about a five-gallon capacity, so five pounds of grain is pretty much the maximum to feed at one time,” says Crandell. “If you give your horse more, he can eat it, but the grains aren’t broken down or adequately prepared for proper digestion.”

A more gut-friendly option is to feed smaller, equal-size portions often, at the same times throughout each day, allowing slow and steady digestive action. Not only do smaller portions aid the digestive process, but the presence of food in the stomach keeps acid levels lower and the horse better hydrated. “When a horse gets a bolus, a mass of chewed food, as is common with twice daily feeding, the rapid production of fatty acids draws water into the colon,” says White. “When the body senses the dehydration it draws the water back into the bloodstream. That process can first dehydrate the blood and subsequently the colon.”

Management Tactics to Prevent Colic

• Keep him moving. What goes on outside your horse can affect his inner functions to a remarkable degree, giving your management routines a major role in gut health. Take the lead from the way your horse would voluntarily structure his day: spending most of his time grazing and ambling about.

Over and over, research studies of predisposing factors in colic cases find that horses who spend the greatest part of the day standing in stalls are much more prone to abdominal disease than those who live in turnout situations. Turnout with compatible companions keeps horses happy, allows them social interaction and gives them the opportunity to let off some steam in addition to consuming their favorite food. Not only is the horse free to consume the ideal fibrous diet, but the simple, continual act of stepping to reach one bite, then the next and the next keeps the food sloshing along in the gut and is believed to increase intestinal motility.

“Peristalsis, the contraction of the intestinal wall, carries the food through to the next portion of the gut,” says Harman. “The horse’s motion keeps a tone to that whole system.” Even if your horse lives in a situation where he can’t enjoy continual turnout, be diligent in seeing that he gets daily exercise. Light to moderate controlled exercise in a paddock, on the longe line or under saddle contributes to better digestion.

• Get sand out of the ration. Sand is one of those substances that, in individual pieces, is inconsequential, but cumulatively, can be disastrous to the horse’s inner workings. Horses may ingest sand along with grain or hay that is fed directly from the ground. They may also swallow sand particles while closely grazing pastures that grow on sandy soil. The risk for horses is greatest in areas where sand is omnipresent, such as coastal states and desert regions.

Because it is heavier than other swallowed materials, sand settles in the horse’s large intestine and stays there. “Sand doesn’t get trapped until it reaches the large intestine because it’s a pretty smooth trail up until then,” says Crandell. “But the large intestine has folds and pockets where sand particles can get lodged. The sand irritates the lining, much like the effect of rubbing a piece of sandpaper. Large amounts can cause impaction or blockage.”

One way to reduce your horse’s sand intake is to never feed him from the bare ground. Offer grain in an untippable bucket or tub and hay from a rack or net with a catch pan or pad of nonearthen material, such as wood, metal, concrete or rubber matting. Another measure is to limit or reduce the number of horses sharing a field or paddock. Overstocking is a sure way to ruin the grass cover and force horses to grub in the dirt for their bits of roughage–and sand.

If possible, keep horses out of pastures and paddocks that have developed bare spots due to overgrazing or drought until new turf is reestablished to cover the earth. Feeding supplemental hay in these stressed pastures also helps reduce the amount of close grazing the horses practice.

Controlling Parasites to Prevent Colic  

While turnout can go a long way in aiding your horse’s digestion, exposure to parasites can undermine that effort. Dozens of species of parasitic worms, some as long as a piece of spaghetti and others, invisible to the naked eye, may reside in your horse’s gut to feed, grow and reproduce. Each parasitic species gravitates to a different part of the body; gut dwellers often choose the large intestine, because it provides the eggs with easy access to the outside environment, where part of their life cycle plays out.

Horses typically ingest parasites orally by grazing near manure in paddocks or fields. The parasites, in the larval stage, travel specific pathways through the internal organs until they arrive in the gastrointestinal tract. There they mature and reproduce. The eggs laid in the digestive tract are passed outside in manure and once outside, the larvae emerge and continue to grow until they are ingested by grazing horses.

Parasites cause colic in several ways. Small strongyle larvae, for example, burrow into the lining of the cecum and colon, where they can live for six weeks to 2 1/2 years. When dormant in a fibrous cyst, these larvae cause little distress to the horse, but when they emerge from these enclosed capsules, they release secretory and excretory material that irritates the gut. The larvae do further damage as they burrow out of the intestine to breed and lay eggs. Large strongyles are often responsible for the more severe colic attacks. Strongylus vulgaris, one of the most harmful parasites to the horse, invades the main arterial supply of the gut and can constrict or plug up blood vessels, cutting off blood supply. When the larvae break out of the arterial walls, they enter the bloodstream which can carry them to any part of the small or large intestine. Those that go astray can damage other organs. 

• Remove manure from paddocks and fields. Since horses ingest parasites by grazing near manure, the best way to avoid this exposure is to remove the piles of manure. Craig Reinemeyer, DVM, PhD, at East Tennessee Clinical Research, Inc. in Knoxville, suggests removing manure in fields twice weekly. An industrial-strength vacuum, like those used to suck up leaves on a golf course or clean parking areas, can also pick up manure. Clear droppings from smaller paddocks with the same equipment you use when cleaning stalls.

Though it’s always a good idea to keep stalls clean and free of muck, removing manure from fields and paddocks does more to reduce your horse’s exposure to parasites, since larvae thrive in certain weather conditions and moisture levels found outdoors. “For strongyles, it’s fairly essential that the eggs drop out in a pasture habitat or around vegetation,” says Reinemeyer. “Their micro habitat is in the grass. Stalls are either too dry, or their source of moisture there is urine and ammonia, and that has a bad effect on larvae.”

If you have an abundance of acreage and intend to rest a field to allow the parasites to die off, plan on waiting for a while. According to Reinemeyer, parasitic larvae are hardy and resistant, particularly to cold weather, and easily can survive for six to seven months outside a host. Ascarid eggs can survive in a pasture for years.

“If you have a contaminated field in the fall, the level of contamination won’t drop until late spring or early summer,” says Reinemeyer. “But if you rest the field from spring through the summer, it will become fairly clean. Freezing doesn’t bother them, but temperatures about 85 degrees or more are not conducive to larval survival.”

• Use dewormers effectively. If you can’t block parasites from entering your horse’s system, try to kill them as soon as they do. Anthelmintics, usually in oral paste form, are the most common method of parasite control in this country. They kill the adult worms, thus reducing egg production, and some larvae. Other deworming agents, such as pyrantel added daily to the feed, kill incoming larvae before they can burrow into tissues and grow to adults.

Anthelmintics can be administered in pelleted form or through a nasogastric tube, as well as via oral paste. Deworming programs are most effective when tailored to horses’ living arrangements and the specific parasite threats facing them. Fecal worm counts are a essential for deciding when the parasite burden is sufficient to warrant chemical controls and whether your deworming program is working; otherwise, you may be over- or undermedicating your horses and possibly contributing to the buildup of resistance to deworming compounds.

The Best “Natural” Defense Against Equine Colic

For all the unknowns still associated with equine colic, horse owners are fortunate that many of the basic causes are now recognized, and these reasons are as ordinary—and controllable—as our everyday management practices.

“There are intestinal accidents we don’t understand, but with mild colics, the most common that we see—those easily treated—are most likely due to diet and management,” says White. “It’s the way we feed them and the way they’re kept in stalls… that contribute to colic.”

Colic is rare in horses living in the wild or on large tracts of grassland, simply because they are consuming what they digest best: low-energy, fibrous grasses. In addition, their easy, ambling lifestyle aids digestion and reduces exposure to fecal contamination. We may not be able to recreate this lifestyle in its entirety for our horses, but our everyday care can mirror the most important of Nature’s lessons for good digestive health.

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