Horses are strong, athletic creatures. On the other hand, their digestive systems are more fragile than those of most other livestock. Ruminants with multicompartment stomachs include cattle and sheep. Food is processed in the first half of ruminants’ digestive tracts by saliva produced by chewing a cud. On the other hand, Horses rely on a metabolically complicated fermentation system. Because horses only have one stomach, most of the fermentation takes place in the hindgut.

According to Kenneth Kopp, DVM, a consultant veterinarian in St. Louis, Missouri, the hindgut, which contains the cecum and large colon (or large intestine), receives significantly less attention from owners than the stomach or small intestine, although accounting for the majority of a horse’s GI tract.

“In a 1,000-pound horse, the hindgut is around 25 gallons—tremendous that’s compared to the (2-4-gallon) stomach,” he explains. “The stomach makes up only 10% of the GI system, but it gets so much attention.” The hindgut is home to billions of microorganisms, including protozoa, fungus, and bacteria. Their responsibility is to convert carbs to fatty acids and offer energy to the horse. Feed or forage may stay in the hindgut for up to 48 hours, compared to only a few hours or fewer in the small intestine.

“Ideally, water-soluble carbohydrates and easily digestible proteins are already broken down and absorbed by the time food reaches the hindgut,” explains Amy Biddle, Ph.D., an assistant professor of animal science at the University of Delaware’s Department of Animal and Food Sciences in Newark. “The fibrous element of the feed, structural carbohydrates, travel right through the small intestine and into the hindgut, where bacteria are very good at breaking them down and converting them to energy sources that the horse can use.”

According to Biddle, short-chain fatty acids, which constitute at least 46 percent of the horse’s energy storage, are likewise absorbed through the hindgut. It is vital to maintain those bacteria happy and functioning correctly for this and other reasons.

Although academics, veterinarians, and nutritionists are aware of the importance of hindgut function to overall health, they are far less knowledgeable about this digestive system section than others. They can’t use imaging equipment to investigate the hindgut, and physicians don’t perform autopsies on horses as frequently as they do on food animals. Small areas of the hindgut can be seen through the abdominal wall with ultrasound. Although visibility is still limited, the colon can be reached using a GI “smart pill” endoscopic camera. To help horse owners nurture a healthy hindgut, researchers look to studies in humans and other livestock species, as well as existing equine digestive system research.

Preserving the status quo

According to Biddle, the hindgut is naturally more basic than the rest of the digestive system. Large grain meals and abrupt dietary changes might boost the growth of lactic acid makers, which can cause lactic acidosis, a severe condition in which the increase in acidity wipes off the beneficial bacterial population in the hindgut.

“This is why it’s crucial to change feeds gently,” adds Biddle, “so the microorganisms in the hindgut can keep up, and the system isn’t stressed.” “It has to be introduced gently, especially if you’re switching to a diet richer in nonstructural carbs (simple sugars and fructans, which are easily digested).”

The greatest way for maintaining a healthy hindgut is to get back to basics and simplify meals. According to Anthony Blikslager, DVM, PhD, Dipl. ACVS, head of the department of clinical sciences and equine surgery and gastroenterology professor at North Carolina State University’s College of Veterinary Medicine in Raleigh, “you want to feed your horse a diet that is high in forage and low in grains.”

Horses arose from the ever-changing grasslands of the margins. They were browsers who evolved into grazers who required constant food intake.

Fresh grass is the ideal fodder for horses, according to Blikslager, but high-quality hay is the best place to start when it comes to improving the equine hindgut. He believes that by altering the forage in the diet, you can correct about 80% of a horse’s condition.

“When we notice horses struggling to hold their weight or running out of steam, we look at their nutrition to see if any minerals or vitamins are missing, especially in certain (regions),” he explains.

According to Biddle, the National Research Council standards for nutrient requirements in horses are an excellent resource for constructing a diet based on forage. She also suggests using tools such as FeedXL’s nutrition calculator to assist in the planning and evaluating individual diets. For example, performance horses, working horses, and lactating mares have higher energy requirements and demand more energy-dense meals.

When Things Don’t Go As Planned

Colic or abdominal pain is the most visible symptom of the hindgut’s not working properly. Even slight irritability, particularly when touching a horse’s belly, could indicate an upset hindgut. A horse that is “not cooperating” on the ground or in the saddle may be experiencing some discomfort.

Kopp has noticed affected horses who enjoy hay but dislike food or digest it slowly in his practice. He’s also regularly witnessed horses shifting their weight from one hind leg to the other.

“It’s not colic,” he continues, “but is there any low-grade inflammation in that hindgut?” “Maybe the horse needs fodder supplements for greater hindgut health if we start seeing some of those things.”

Leaky gut is the next most prevalent problem. A thin layer of cells lines the whole intestinal tube, forming a barrier against stomach acid. According to Kopp, the cells line up side by side and adhere similarly to Velcro. Leaking can occur if their integrity is compromised.

“When pathogens (disease-causing organisms) escape into the bloodstream from the gut, inflammation can occur everywhere in the body,” Kopp adds. “What researchers are discovering is that this leakage and inflammation cycle may increase the risk of pneumonia and mastitis (inflammation of the mammary glands) in horses, as well as allergies and autoimmune disorders.”

Another result of poor hindgut health is laminitis (a hoof illness in which the laminae—tissues that suspend the coffin bone within the hoof—become injured and inflamed). The blood arteries in the horse’s foot are so sensitive that they cannot withstand abrupt changes. Acidosis can cause bacteria to die and release endotoxins if a substantial amount of undigested starch (e.g., from grain overload) enters the hindgut. Endotoxins can cause laminitis if they enter the horse’s system unexpectedly, according to Blikslager.

The most common kind of hindgut-related laminitis, according to Kopp, is pasture-associated laminitis in horses with equine metabolic syndrome or pituitary pars intermedia dysfunction (also known as equine Cushing’s illness), with insulin poisoning of the laminae as the primary mechanism.

“In other species, mild leaky gut has been associated with insulin resistance and metabolic syndrome, and it could very well be part of the problem in equines,” adds Kopp. “In horses, chronic low-grade leaky gut may help explain insulin resistance and the risk of laminitis.”

Kopp looks to human and food animal research for answers because we don’t completely understand leaky gut’s whole-body impact on horses. He cites research done in piglets by Adam Moeser, Ph.D., DVM, a professor at Michigan State University College of Veterinary Medicine, closely resembles studies on children and the long-term effects of early weaning.

According to Kopp, “findings demonstrate that weaning stress early in life contributes to permanent GI disorders.” “Irritable bowel syndrome and chronic gut difficulties were observed in the kids who were followed later in life, and Adam is seeing that in the piglets.” They are more reactive to stressful conditions later in life if they start leaking early in life.”