1. Maximize pasture turnout. Overall, the key to keeping a horse’s digestive system functioning well is to mimic nature as closely as possible. Horses with access to ample pasture will spend as much as 18 hours a day grazing, and that’s exactly what their digestive tracts are designed for—a near continuous supply of chewed grass. Horses on full turnout almost never experience colic.

Of course, that’s not always possible. Some horses have issues, such as a susceptibility to laminitis, that require their access to pasture be limited. And some easy keepers simply get too fat if allowed to graze around the clock. But even those who must have their grass intake limited—with a muzzle, perhaps—will still benefit from the exercise and socialization they gain from being at liberty in their pastures.

2. Feed good quality hay. “The most important thing in the diet is the forage component,” says Stephen Duren, PhD, an equine nutritionist at Performance Horse Nutrition. “Everything revolves around good forage. The money spent on good-quality hay is like money in the bank, regarding your horse’s health. It will decrease the number of veterinary calls—the number of colics or digestive upsets.”

If your horse’s teeth are in good shape but he seems to waste large quantities of hay, take a close look at the bales. “The appearance, color and smell can tell you a lot about its quality and digestibility,” explains Duren. “The longer and larger the stems, the less digestible it is. As plants grow taller and become more mature, they are less like grass and more like trees, with less protein and other nutrients, and more lignin, the fibrous part of the structure. In the instances where hay might not be top quality or might contain sticks or other undesirable portions, we usually feed more than the horse needs so he can sort out the parts he doesn’t want to eat.”

3. Don’t let your horse’s stomach empty out. Gastric ulcers are common in horses, in part because of the modern feeding practice of restricting a horse to one or two large meals per day, which leaves his stomach empty most of the time.

“The horse’s stomach is always producing acid,” says Duren. “His GI tract is designed for continuous grazing and doesn’t have the ability to shut off acid production. The main buffer for acid in the stomach is saliva. The horse produces about twice as much saliva daily when eating hay or grass than when eating grain.”

Feeding hay free-choice allows a continuous intake and keeps the horse’s stomach full longer. So, too, can dividing the hay ration out into smaller portions that are fed throughout the day. In addition, consider including a little alfalfa in the mix, says Duren: “Some research at the universities of Tennessee and Kentucky found that alfalfa hay was more efficient in buffering against stomach ulcers than grass hay, due to the higher level of calcium in the alfalfa. The protein and calcium can both act as potential buffers for stomach acid. Now most Thoroughbred trainers feed a small amount of alfalfa and try to have it already in the stomach when horses go out in the morning to work.”

4. Go easy on the grain. Some horses—growing youngsters, broodmares, elderly pensioners, hard-working athletes, for example—require more calories and nutrition than forage alone can provide. For centuries, the solution had been to give horses grains and, more recently, other nutrient-dense feeds.

However, grains are high in sugars and starches, which when consumed in too high a quantity at once can cause colic or laminitis. This makes sense when you consider how a horse’s digestive tract functions: In order to utilize a fibrous food like grass, herbivores must ferment the chewed matter to extract the nutrients. Most herbivores are ruminants—animals such as cows, sheep, goats, deer and camels have multiple stomachs, one of which serves as a large fermentation area. Horses have a relatively small, single stomach (holding two to five gallons, compared to a cow’s, which holds 15 to 30), followed by the small intestine; then the horse has a large cecum and hindgut, which is where his fermentation occurs. “The horse’s tract is designed to get food down to the hindgut as swiftly as possible,” says Anthony Blikslager, DVM, PhD, of North Carolina State University.

“If you feed a lot of grain/sweet feed, the horse will not be able to absorb all the sugar from it before it gets to the cecum and colon,” says Blikslager. “The hindgut is designed to digest grass, and if all of a sudden it gets sugar, this has an adverse impact on the microbial population. It changes the pH and type of bacteria. The bacteria that can digest sugar quickly multiply and form a lot of gas in the process.”

5. Offer hay first, then grain. “Horsemen often ask me whether they should feed hay and grain at the same time and let the horse decide which to eat first,” says Duren. “From a digestibility and health standpoint, the hay should always be fed first.”

The horse has a small stomach and food moves through it quickly, he explains: “If you feed hay and grain at the same time, most horses will eat the grain first because they like it, following it with hay and water. This ends up pushing the grain through the stomach and small intestine too quickly to be digested thoroughly.” As a result, the sugars and starches reach the hindgut unabsorbed, where they can cause problems.

“For the morning feeding, your horses will be healthiest if you go through and feed every horse in the barn their hay, go eat your own breakfast and then come back after the horses have eaten some hay, and grain them,” he suggests.

6. Replace some carbohydrates in your horse’s diet with alternative caloric sources. Vegetable or corn oil are commonly used to help keep weight on older horses, as well as to add energy to the rations of high-performance horses. Corn oil is a popular choice because it’s inexpensive and horses generally find it palatable, but flax, canola and other products are also acceptable.

Oil is readily absorbed and doesn’t contain any starch or sugar, so it’s a safer way to increase calories in a ration than grain. Adding oil to the diet can also reduce the risk of ulcers: “Fat slows the rate at which the stomach empties, and this keeps more material in the stomach longer, which helps keep the acid levels under control,” says Duren. As a bonus, oil will give your horse’s coat a healthy sheen.

Another option for safely adding calories to your horse’s diet is one of the newer feeds, incorporating beet pulp or soybean hulls, which provide fiber as well as energy. “A high-fiber commercial feed is usually better than straight grain or sweet feed,” says Blikslager. These feeds contain less starch and sugar and are digested more like roughage than grains, and so they reduce the risk of serious gas colics and laminitis. “They have a high calorie content on a dry-weight basis,” explains Duren. “They have about the same energy value as oats but are safer to feed because they are more fibrous.”

7. Never limit fresh water. Horses need as much water as they will drink. Just chewing and digesting dry forage itself requires plenty of fluid; even more crucial is keeping enough water in their systems to keep ingesta moving. If there’s not enough, the ingesta can dry and form impactions that block the further flow of food, causing potentially fatal colic. The average horse needs to drink up to seven gallons per day. The actual amount may vary, if for example he’s eating drier hay or, conversely, grazing water-rich grass. Most horses naturally drink what they need if they have access to clean water.

However, check your horse’s water daily to make sure it’s not too hot or too cold—both extremes can discourage drinking. “I recently had some colic cases in Arizona where a farm’s water system was above ground,” says Duren. “The water was pumped from a well and piped through the ceiling to each stall in the barn. The pipes got too hot during the summer heat and the horses wouldn’t drink the water.”

In cold weather, if you’re using heated water tanks/buckets, put your ungloved hand in the water to make sure the units are properly grounded. If you feel a tingle, electricity may be deterring your horse from drinking.

Above all, don’t withhold water from a horse after exercise. The myth that allowing hot horses to drink cold water will lead to muscle cramps and colic has been thoroughly disproved by several studies.

8. Provide plenty of exercise. Horses are designed to keep moving. “The smooth muscle contractions of the gut are aided by movement and exercise,” explains Duren. “Horses in stalls don’t have as much stimulation for the tract as a horse out on pasture walking around.”

Fortunately, even the amount of exercise a horse gets walking around the pasture while grazing is enough to reduce the risk of impactions and gas buildups. Of course, any time spent at liberty is beneficial: “If horses are stalled, it helps to turn them out daily for a while in a pen or riding arena, even if it’s only 20 minutes, allowing them to run and buck and play,” Duren says. “Activity helps stimulate gut motility.”

9. Keep your horse from ingesting too much sand. In general, it’s best to feed hay off the ground. When a horse lowers his head to eat, gravity helps drain fluids containing dust and particles out of his nose and sinuses. However, if you have sandy soil, a horse who eats off bare ground may ingest enough of the particles to form “dams” that block the intestine, a condition called sand colic.

If sand is an issue for your horse, place your hay in a feeder or hay net, or feed off a stall mat on the ground. Commercial feeders are available, but a number of “found” items, such as a leaky but structurally sound water trough, will also serve the purpose. “It helps to feed on something you can sweep off between feedings to keep it free of dust and debris, and minimize the horse’s exposure to sand,” says Duren.

You may also want to add psyllium to your horse’s diet as a precaution. A proven laxative, psyllium is made from the ground seeds of the Plantago plants; when ingested, it swells and forms a gel-like substance that helps push sand through the intestine; it is especially helpful when combined with oil.

10. Protect your horse’s gut flora. A horse needs a healthy, well-balanced population of microbes in his gut to help him digest food and absorb nutrients. Some of these microorganisms are essential for creating necessary nutrients as well. Many factors in a horse’s life—including the stresses of transport and competition or the administration of antibiotics—can disrupt this microbial population. If the good flora levels drop too low, the horse may develop chronic diarrhea, he may lose weight or just generally fail to thrive, or he may become susceptible to various types of colic.

To help a horse replenish and maintain healthy populations of gut flora, a number of supplements are available that contain probiotics, live microorganisms to “reseed” the gut. Many also contain prebiotics, nutrients which feed the beneficial bacteria. Some prebiotics also contain nondigestible sugars that bind with pathogens and carry them out of the gut with manure.

“I feel it’s beneficial to have a small amount of these important microbes added to the diet on a daily basis,” says Amy Gill, PhD, an equine nutritionist with a practice in Lexington, Kentucky. “The life cycles of these microbes are short. It’s better to have them available in each feeding, as opposed to waiting until something bad happens and then trying to fix it.” Direct-fed microbials (DFM) are available in some commercial feeds as well as supplements.

As always, consult with your veterinarian or an equine nutritionist before making any changes in your horse’s diet, especially if you are trying to address a specific issue. With guidance, you may well find several ways to safeguard your horse’s digestive health.