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Getting back to basics might be the key to keeping the largest portion of the horses GI tract functioning properly

Horses are powerful, athletic animals. Their digestive systems, however, are delicate compared to those of most other types of livestock. Ruminants such as cattle and sheep have multicompartment stomachs. Saliva created by chewing a cud processes food in the front half of ruminants digestive tracts. Horses, however, rely on a metabolically complex fermentation process. And because horses only have one stomach, most of that fermentation occurs in the back part or hindgut.

Despite making up the largest portion of a horses gastrointestinal (GI) tract, the hindgut, which includes the cecum and large colon (or large intestine), often receives far less attention from owners than the stomach or small intestine, says Kenneth Kopp, DVM, a consulting veterinarian based in St. Louis, Missouri.

The hindgut is about 25 gallons in a 1,000-pound horsethats huge compared to the (2-4-gallon) stomach, he says. The stomach is only 10% of the GI tract, but theres such a focus there. Billions of microorganisms, including protozoa, fungi, and bacteria, live in the hindgut. Their job is to convert carbohydrates into fatty acids and provide the horse with energy. Feed or forage might spend as much as 48 hours in the hindgut compared to a few hours or less in the small intestine.

Ideally, by the time material gets to the hindgut, water-soluble carbohydrates and easily digestible proteins are already broken down and absorbed, says Amy Biddle, PhD, assistant professor of animal science in the University of Delawares Department of Animal and Food Sciences, in Newark. The fibrous part of feed, structural carbohydrates, are passed right through the small intestine to the hindgut, where the bacteria are really good at breaking them down and converting them to energy sources that the horse can utilize.

The hindgut also absorbs short-chain fatty acids, which Biddle estimates provide at least 46% of the horses energy stores. For that and other reasons it is critical to keep those microorganisms happy and functioning properly.

Although researchers, veterinarians, and nutritionists know how critical hindgut function is to overall health, they know much less about this part of the digestive system than others. Generally, theyre unable to examine the hindgut with imaging equipment, and clinicians dont perform autopsies in horses as frequently as they do in food animals. Veterinarians can use ultrasound to see small portions of the hindgut through the abdominal wall, and they can reach the colon with a GI smart pill endoscopic camera, but visibility is still limited. For the most part, researchers look to studies in humans and other livestock species and existing equine digestive system research to help horse owners promote a healthy hindgut.

The hindgut is naturally more basic than other parts of the digestive system, says Biddle. Large grain meals and sudden diet changes can promote the growth of lactic acid producers that rapidly shift the pH level in the hindgut and can lead to lactic acidosis, a dangerous situation in which the acidity increase kills off the beneficial bacterial population.

This is why it is important to change feeds so slowly, so the microbes in the hindgut can keep up, says Biddle, and so abrupt changes do not stress the system. Especially if youre going to change to a diet higher in nonstructural carbohydrates (simple sugars and fructans, which are readily digested), it has to be introduced slowly.

Getting back to basics and simplifying meals is the best approach for maintaining a healthy hindgut. Ideally, you want to feed your horse a diet thats high in forage and low in grains, says Anthony Blikslager, DVM, PhD, Dipl. ACVS, head of the department of clinical sciences and equine surgery and gastroenterology professor at North Carolina State Universitys College of Veterinary Medicine, in Raleigh.

Horses evolved on ever-changing marginal grasslands. They were browsers that adapted to be grazers that rely on continual forage intake. This article continues in the February 2021 issue of The Horse: Your Guide to Equine Health Care. Subscribe now and get an immediate download of the issue to continue reading. Current magazine subscribers can access the digital edition here.

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Keeping the Horse's Hindgut Happy The Horse - TheHorse.com

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