Equine Gastrointestinal Health Reviewed
All horses’—from young to old, high-performance to sedentary, rescued to syndicated, and everywhere in between—gastrointestinal (GI) tracts function in the same manner. And owners of all types of horses should take the same steps to help keep their animals’ GI systems functioning optimally.

At the 2013 Alltech Symposium, held May 19-22 in Lexington, Ky., Jo-Anne Murray, PhD, PgDip, PgCert, BSc(Hons), BHSII, RNutr, FHEA, presented a lecture on equine gastrointestinal health. Murray is a senior lecturer in Animal Nutrition and Husbandry at the University of Edinburgh’s Royal (Dick) School of Veterinary Studies, in Scotland.

The horse’s gut is an “amazing organ,” Murray said. In simple terms, the GI tract is a tube running from the horse’s mouth to his rectum that takes in and processes feedstuffs, she said. It is divided into two sections: the foregut and the hindgut. The foregut—which consists of the esophagus, stomach, and small intestine—digests feedstuffs through the action of enzymes, while the hindgut—comprised of the cecum, large colon, small colon, and rectum—digests ingesta (primarily forage) with microbes through fermentation, she said. The entire GI tract plays an important role in the horse’s overall health and disease status, she noted.

Factors Negatively Impacting GI Health

In most cases, today’s domestic horse eats a very different diet than the species evolved to consume. Some of these differences, Murray said, could negatively impact horses’ GI health.

Horses evolved to roam up to 80 kilometers (nearly 50 miles) per day and graze for 16 to 20 hours daily on low-quality, high-fiber forage. They’re designed to take about two mouthfuls of forage in one spot before moving on, she said. This frequent grazing means horses will chew about 60,000 chews per day; because horses can only produce saliva when they chew, this means their stomach stays well-buffered with the substance, protecting it from gastric ulcer development.

Today, Murray said, most domestic horses will roam about 20 kilometers (about 12.5 miles) each day and generally consume a diet consisting of concentrated energy sources, such as well-managed pastures. Well-maintained, higher quality pastures generally have a higher nonstructural carbohydrate (NSC) content than the low-quality forage horses evolved on, she said, and high-NSC diets have been associated with health issues including colic, laminitis, and gastric ulcers.

Another factor that can negatively impact GI health is how owners feed horses. While consuming large meals at set times throughout the day is common practice for humans, the same regimen isn’t ideal for horses, Murray said. For instance, feeding horses two large meals consisting of cereal grains or concentrates and forage each day decreases the amount of saliva the horse produces as he chews. This decreased saliva production leaves the upper portion of the stomach at risk for gastric ulcer development. Additionally, she noted, large meals have been shown to decrease the small intestine’s digestibility.

Abrupt diet changes can also cause serious problems for the horse’s digestive tract, Murray said. Feed changes affect the microbial populations that colonize horses’ GI tracts, decrease digestibility, and can cause ill health, such as colic or laminitis.

Maintaining Good GI Health

In light of the factors that can negatively impact a horse’s digestive tract, how can horse owners keep their charges’ GI systems healthy? Murray provided some recommendations.

First, she said, make any diet changes gradually. It can take the horse’s GI tract up to a month to adjust to different types of feedstuffs, even if the change is from large amounts of concentrates to a more forage-based diet. She recommended spreading feed changes over a period of two to three weeks. Additionally, she said, a rapid increase in lush pasture consumption can be especially dangerous to horses. Like any other feed change, introduce pasture gradually.

Next, carefully consider what types of feed you’re providing and how much your horse is consuming, and, if possible, make changes accordingly and gradually. Murray recommended providing horses with a diet high in fiber and low in cereal grains or concentrates. The latter feed types do have their place in some equine diets, she said; the trick is using them appropriately with forage as the diet’s base. Murray recommended feeding no more than 1 gram of starch per kilogram of body weight, or approximately 1.25 kilograms (about 2.74 pounds) of cereal grains or concentrates per meal for an average 500 kilogram (about 1,100 pound) horse. If a horse is consuming a forage-only diet, Murray recommended providing a 500 kg horse with about 10 kg of forage per day, and noted an average size horse should never consume less than five kilograms of forage per day. Additionally, she said, ensure the horse receives a consistent amount of feed daily.

Finally, Murray said, consider adding pre- or probiotics and yeast to horses’ diets, both of which can potentially influence the horses’ intestinal microflora. Prebiotics are food components that stimulate hindgut microflora activity and growth. The horse does not digest these ingredients; rather, hindgut microbes do. Probiotics, or direct-fed microbials, are the bacteria typically found in the horse’s intestinal lumen. Murray said research has shown that certain species of both pre- and probiotics can have beneficial effects on horses’ digestive systems. Additionally, she referenced one study showed that horses consuming a yeast supplement showed a numerical (albeit not significant) difference in the number of starch degraders compared to horses not consuming the supplement. Essentially, she said, “It means that feeding yeast may decrease the risk of gastrointestinal disturbance associated with high-starch diets.”

Take-Home Message

The horse’s GI tract and the diet it digests are integral to maintaining good overall health, Murray concluded. Feeding consistent amounts of a high-fiber, low-NSC diet can help maintain good GI health, as can making feed changes slowly and carefully. If questions arise about a particular horse’s dietary needs, consider consulting with a veterinarian or equine nutritionist.