Gastrointestinal Tract Health for Top Performance in Horses

The importance of nutrition in deriving maximal performance from equine athletes is undeniable. Without well-balanced diets, horses cannot perform, and without a well-functioning gastrointestinal tract, horses cannot adequately transform diets to performance fuel.

A thorough understanding of the equine gastrointestinal tract will enhance your knowledge of digestion and will help you get the most out of your horse and the feedstuffs you dole out to him. Certain aspects of the tract are more influential than others, and focusing on these will help support top performance.

Mouth

The teeth get the lion’s share of attention when considering the digestive functions of the mouth. It’s understandable, though, as the incisors (the front teeth) are responsible for grasping certain feedstuffs, and the molars (the cheek teeth) are in charge of grinding feed, breaking it into pieces that are more manageable for the remainder of the tract.

Modern management scenarios have brought about unusual problems with teeth. Through the introduction and widespread allocation of hard feeds (textured and pelleted concentrates), horses now have a greater tendency for dental deformities, especially of the incisors.

Deformities are easily remedied through regular evaluation and correction by a professional equine dentist or a veterinarian who specializes in dentistry. Correcting hooks, points, and wave mouths are all part of a day’s work for these professionals, and once amended properly, teeth are able to process feeds without problem.

Lack of appropriate dental care will eventually manifest as an inability to maintain weight. Failure to chew properly may also contribute to problems further along the gastrointestinal tract.

The tongue assists in transferring feed from the front of the mouth to the back, preparing it for swallowing. Injuries sometimes occur to tongues, usually through improper bitting or accidents, and it’s not unusual to see chunks of tissue removed from the organ or the tongue sliced entirely from side to side. While ingestion might be impacted temporarily as an injury heals, tongue wounds rarely impede long-term chewing or swallowing.

Horses have three pairs of salivary glands. In an average-sized, mature horse, the largest of the pairs, the parotid, can produce more than 2.5 gallons (10 liters) of saliva daily. Few disorders of the salivary glands have been noted, though hypersalivation occurs following ingestion of slaframine, a toxin produced by a fungus that plagues certain varieties of clover.

Management tip: Locate a well-respected equine dentist or veterinarian and pay for his or her services at least once a year. Older horses and those with abnormal jaw conformation (parrot mouth or monkey mouth) might require more frequent visit. Young horses should be evaluated as frequently as mature horses, and problems should be addressed immediately.

Stomach

Passage of ingesta (chewed-up feed) from the mouth to the stomach rarely encounters problems, except in cases of choke or obstruction of the esophagus, which can be caused by nearly any feedstuff that is gulped down. Horses that have a history of choke, even if one only one prior occasion, seem to be predisposed to recurring episodes. Immediate veterinary attention is required in cases of choke.

The horse’s stomach accommodates only 2 to 4 gallons (7.5 to 15 liters) of ingesta, which is markedly less than the stomachs of similar-sized animals. Stomach volume dictates meal size, so horses are therefore incapable of efficiently processing large meals.

A medley of gastric enzymes and acids are secreted by the stomach. These liquids are incredibly efficient at further breaking down feeds and preparing nutrients for absorption, or the transfer of nutrients across gastrointestinal membranes and into the bloodstream for use through the body.

The constant acid production can be a menace to performance horses, especially those that are stabled for long periods of time without free-choice access to good-quality hay.  Regular forage consumption supports stomach health in two ways: the constant flow of saliva that lubricates feed for chewing and swallowing aids in reducing acidity of the stomach, and stomach fill gives the acid an appropriate outlet on which to work, saving the delicate stomach lining from erosion and the eventual formation of ulcers.

Gastric ulcers are a well-known source of problems for performance horses. Though these lesions affect horses differently, it is not uncommon for horses to be sour and unwilling to work, experiencing a noticeable decline in performance. Clinical signs might include loss of weight, dull coat, and lethargy.

Management tip: If a horse has experienced choke previously, use precautions to avoid it in the future. Spreading hay and grain over a large surface provides an artificial grazing area and encourages nibbling rather than gobbling.  If wolfing grain is the problem, devise a method that slows consumption. In the past, horse owners have placed large, smooth stones in a trough, which precluded bolting of feed. A specially designed feeder is now on the market for such horses. It features several small, shallow wells that are filled with feed. The horse has no problem getting the feed and consumption is slowed considerably.

Management tip: Provide horses with forage at all times. Quality of forage depends on the horse. An easy keeper might need mediocre-quality hay or pasture, but a hard-keeper may require a high-quality variety. Calorie-rich alfalfa (lucerne) is thought to have inherent buffering properties, so it would be especially appropriate for a hard keeper prone to gastric ulcers. If forage cannot be available at all times, take precautions to prevent gastric ulcers by using a supplement that contains a buffering agent.

Small Intestine

From the stomach, ingesta flows into the small intestine. New research has indicated that ulcer formation may occur in the duodenum, the segment of small intestine closest to the stomach, though this is a novel area of study and information is limited. From a digestive perspective, the small intestine is vital because it is the absorptive capital for protein, vitamins, and minerals. Advances in feed-manufacturing technology have led to the development of mineral forms that have greater absorption rates.

Chelation is the chemical process by which a mineral (iron, cobalt, copper, zinc, manganese) is combined with a mixture of amino acids and peptides. The resulting substances are known as chelates. These chelated minerals are thought to be more digestible than nonchelated forms. In other words, chelation makes the minerals more bioavailable (able to be absorbed and used for bodily functions), chiefly by shielding them from the effects of other dietary elements in the horse’s digestive tract. Chelates are described as organic minerals in contrast to inorganic minerals, those that are not bound to amino acids.

Management tip: Purchase high-quality feeds that contain chelated minerals. If you’re unsure whether your feed includes these easily absorbed ingredients, ask your feed manufacturer for clarification.

Hindgut

The hindgut is a collective term for the cecum and the colon. The colon is further segmented into the large colon, transverse colon, and small colon.

The cecum is the epicenter of forage digestion, due to the fermentation capability of the billions of microorganisms that reside there. Digestion of fiber results in the production of energy that is vital for fueling everyday work and play. Fiber digestion by the microbial population continues on through the segments of the colon, particularly in the areas that are most capacious.

There are times, though, that the cecum does not function at full capacity. Among performance horses, one of the likeliest causes hindgut acidosis.

Because performance horses must often eat rations containing large volumes of concentrates, starch sometimes leaves the small intestine undigested. Unfortunately, the cecum is not the best place for starch digestion. As cecal microorganisms ferment more and more starch, the environment changes considerably, becoming increasingly acidic. With the swell in acidity, a population shift occurs among the microorganisms, with many beneficial species dying off.

An unstable microbial population sometimes causes problems with weight loss, reluctance to eat, poor performance, recurrent low-grade colic, and commencement of certain stable vices (wood-chewing and cribbing).

Management tip: Feed small meals, no larger than 5 pounds (2.2 kilograms), so starch digestion is complete by the time ingesta enters the cecum. It is not unusual for horses to be fed three or more small meals a day when large quantities of feed are necessary to maintain body condition and meet energy requirements. Space meals throughout the day to allow the gastrointestinal tract time to function at optimal capacity.

Management tip: Lower the risk of undigested starch entering the hindgut by choosing a concentrate that is higher in fat and fiber, or by selecting a concentrate that contains grains that have been steam-flaked, micronized, pelleted, or extruded, which have higher prececal digestibility.

Management tip: In addition to high-grain diets, hindgut acidosis can be caused by fructan-rich pastures. The same mechanism is at work: the small intestine becomes overwhelmed with starch and is unable to properly process it, and the undigested starch moves on to the cecum, where fermentation causes a downshift in pH.

Management tip: A hindgut buffer can help moderate drastic swings in the acidity of the hindgut. The buffer should be encapsulated, so it is not released until it enters the cecum of the horse, exactly where it’s needed.

Rectum

As ingesta travels through the colon towards the rectum, nutrients continue to be absorbed into the bloodstream for body-wide use. As it gets closer to the end of its journey, less digestion occurs and more water is resorbed from the indigestible matter, which allows for the formation of normal manure.

Changes in manure texture can sometimes reveal problems. Manure that is excessively moist and certainly diarrhea are signs that something might be amiss with the gastrointestinal tract. Veterinary attention should be sought if no clear reason for the change in manure can be traced (no changes in diet or environment; no temporary excitement, etc.). On the flip side, manure that is excessively dry could be an indication of insufficient water intake. Water sources should be checked to ensure horses have no limitations on intake such as insufficient supply or dirty container.

Management tip: Normalizing chronic loose manure is sometimes achieved through the use of probiotics or yeast products. A hindgut buffer may also help with this problem.