And how you can improve it

Text: Ricolette du Preez, Founder of Supreme Equine Nutrition and Independent Equine Nutritionist, (BTEC) Professional Dip in Equine Nutrition (UK), BSc Dietetics.

Gut health plays a fundamental role in the overall wellbeing, performance, recovery, and behaviour of horses. However, many factors can negatively affect or compromise the equine gastrointestinal system and its delicate microbial balance.

Common factors include:

• travel and competition
• intensive exercise
• environmental and seasonal changes
• antibiotic treatment
• dietary changes
• relocation
• temperament of the horse

These factors may alter the gut microbiome and contribute to digestive disturbances and colic, which can present as diarrhoea, flatulence, spasms or even impaction. In more severe or prolonged cases, ongoing gastrointestinal stress may contribute to ulceration, enteritis, gastritis and inflammatory bowel diseases such as colitis.

Supporting gut health

One of the most important ways to support gut health in horses is through appropriate nutritional management. Horses are naturally adapted to consume fibre-rich diets continuously throughout the day. Feeding a diet based primarily on high-quality fibre sources, with very low or no grain inclusion, helps support microbial stability and digestive function.

Beneficial fibre sources may include:

The hindgut microbiome relies on fermentable fibre as a primary energy source. During fermentation, beneficial microbes break down fibre and produce volatile fatty acids, which provide an important source of energy for the horse while also supporting hindgut health.

The equine gut microbiome is highly dynamic and continuously adapts to dietary and environmental changes. Feeding a diverse range of fibre sources may help promote greater microbial diversity, potentially improving the horse’s ability to cope with stress and digestive challenges.

---

Important

When introducing any new feed ingredient, gradual dietary transitions are essential. Slowly increasing inclusion rates over time allows the gut microbiome to adapt appropriately while reducing the risk of digestive upset.

---

Alongside sound feeding practices, several nutritional ingredients have been scientifically investigated for their ability to support digestive health and promote a more stable gastrointestinal environment in horses.

Let us take a closer look at some of the ingredients and the scientific research supporting their role in equine gut health.

Calcareous marine algae and gastric buffering

Calcareous marine algae are a natural source of highly bioavailable calcium and magnesium with significant buffering properties within the equine digestive tract.

In a study by Jacobs et al., 2020, horses supplemented with a marine-derived calcified algae product demonstrated significantly increased gastric pH following feeding. Baseline gastric pH values, averaging approximately 2.3, increased to roughly 5.5 – 5.9 at two hours post-feeding.

The researchers reported that buffering effects remained detectable up to four hours post-supplementation in several horses, suggesting prolonged gastric buffering activity.

Additional in vitro work by Moore-Colyer et al., 2014 demonstrated that marine-derived buffering compounds maintained buffering activity within simulated equine gastric conditions for approximately four to six hours, while also promoting favourable hindgut fermentation dynamics.

Probiotics

Saccharomyces cerevisiae

The live yeast probiotic Saccharomyces cerevisiae has been extensively studied for its ability to support hindgut microbial stability and fibre digestion in horses.

In a study by Medina et al., 2002, horses supplemented with approximately 10⁹ CFU/day of Saccharomyces cerevisiae demonstrated improved stability of hindgut microbial populations when fed high-starch diets. The researchers observed reduced fluctuations in hindgut pH and improved conditions for fibre-fermenting bacteria, suggesting enhanced fermentation efficiency.

Similarly, Jouany et al., 2008 reported improvements in fibre degradation and nutrient digestibility when yeast cultures, such as Saccharomyces cerevisiae, were supplemented in equine diets. The study suggested that Saccharomyces cerevisiae stimulates cellulolytic bacterial activity (activity breaking down cellulose) within the hindgut, assisting fibre utilisation and increasing volatile fatty acid production.

More recently, Ganda et al., 2023, evaluated the effects of a Saccharomyces cerevisiae fermentation product in horses exposed to stress conditions. Horses receiving supplementation maintained greater microbial diversity and stability compared with untreated horses, supporting the role of yeast supplementation in preserving hindgut resilience during stress exposure.

These findings suggest that supplementation with Saccharomyces cerevisiae at levels around 10⁹ CFU/day may be beneficial for horses.

Saccharomyces boulardii

Saccharomyces boulardii is a probiotic yeast, closely related to Saccharomyces cerevisiae, but it is generally used more specifically for gastrointestinal disturbance and diarrhoea support due to its ability to survive within the equine gastrointestinal tract.

In horses with acute enterocolitis, Desrochers et al. administered Saccharomyces boulardii at approximately 10 × 10⁹ yeast cells orally every 12 hours for 10 days. The supplemented horses showed a significant reduction in the duration of watery diarrhoea and overall gastrointestinal illness compared with placebo. This suggests that S. boulardii may be useful as part of a digestive-support strategy during periods of intestinal upset.

Postbiotics

Postbiotics are biologically active fermented yeast metabolites which are produced during the controlled fermentation of Saccharomyces cerevisiae. These compounds may assist in supporting microbial stability, hindgut fermentation, stress resilience, and overall gastrointestinal function in horses. Ganda et al., 2023, evaluated the effects of a Saccharomyces cerevisiae fermentation product in horses exposed to physiological stress. Horses receiving the yeast fermentation product maintained greater microbial diversity and microbiome stability compared with untreated horses during stress exposure.

Prebiotics MOS and FOS

Prebiotics such as Mannan Oligosaccharides (MOS) and Fructooligosaccharides (FOS) act as selective substrates for beneficial gastrointestinal bacteria.

Research by Spring et al., 2000, demonstrated that MOS supplementation supported intestinal microbial balance and gut integrity through modulation of bacterial populations and supported intestinal immune regulation.

FOS has also been shown to stimulate beneficial bacterial growth. Gidson and Roberfroid, 1995, demonstrated that FOS supplementation increased the populations of favourable bacteria such as Bifidobacteria and Lactobacilli, promoting a more stable gastrointestinal environment.

Although the exact optimal equine inclusion rates vary by formulation, commercial equine digestive supplements commonly provide MOS and FOS at gram-level daily intakes designed to support microbial balance during stress, travel, dietary transition, competition, and antibiotic administration.

L-Glutamine

L-Glutamine is recognised as one of the primary metabolic fuels for intestinal epithelial cells and plays a key role in maintaining intestinal barrier integrity.

Wu et al., 2011, highlighted glutamine’s role in supporting tight junction integrity and intestinal cell metabolism. Under stress conditions, glutamine demand increases significantly, potentially compromising intestinal barrier function if insufficient amounts are available.

In both human and veterinary gastrointestinal research, glutamine supplementation has been associated with improved maintenance of intestinal integrity and reduced permeability during physiological stress.

Psyllium husk

Psyllium husk is a soluble fibre commonly used to support gastrointestinal motility and assist in the removal of sand from the equine digestive tract. Research by Lieb, 1993, demonstrated that psyllium supplementation, once mixed with water, can improve sand clearance from the gastrointestinal tract in horses, supporting its use in horses grazing sandy environments or prone to sand accumulation.

Pectin-Lecithin

Pectin forms a gel-like barrier, while lecithin contributes phospholipids that may assist in supporting stomach lining integrity and gastric comfort in horses exposed to gastric stress.

Research by Venner et al., 1999, investigated horses with gastric lesions and suggested that pectin-lecithin supplementation may assist in supporting gastric mucosal protection and stomach health.

Final thoughts

The future of equine nutrition is increasingly centred around the gut. As scientific research continues to uncover the profound influence of the gastrointestinal microbiome on digestion, immunity, recovery, behaviour, and performance, maintaining gut health has become one of the most important aspects of modern horse management. By combining sound feeding practices with scientifically supported nutritional ingredients, horse owners can help create a more stable, resilient, and efficient digestive environment capable of supporting horses through the demands of training, travel, competition, and daily life. Ultimately, a healthier gut may contribute not only to improved digestive wellbeing but also to a healthier, happier, and better-performing horse.

---

References

Desrochers AM, Dolente BA, Roy MF, Boston R, Carlisle S. Efficacy of Saccharomyces boulardii for treatment of horses with acute enterocolitis. Journal of the American Veterinary Medical Association. 2005;227(6):954–959.

Schoster A. Probiotic use in horses — what is the evidence for their clinical efficacy? Journal of Veterinary Internal Medicine. 2014.

Medina B, Girard ID, Jacotot E, Julliand V. Effect of a preparation of Saccharomyces cerevisiae on microbial profiles and fermentation patterns in the large intestine of horses fed a high starch diet. Journal of Animal Science. 2002;80(10):2600–2609.

Jouany JP, Gobert JG, Medina B, Bertin G, Julliand V. Effect of live yeast culture supplementation on apparent digestibility and rate of passage in horses fed a high-fiber or high-starch diet. Journal of Animal Science. 2008;86(2):339–347.

Ganda EK, Burton RJ, Leite MG, et al. Effects of Saccharomyces cerevisiae fermentation products on stress-associated changes in the equine gut microbiome. Animals. 2023;13(6):1021.

Wu G, Bazer FW, Davis TA, et al. Glutamine and intestinal barrier function. Amino Acids. 2011;40(5):1257–1265.

Jacobs BM, Rendahl AK, Furr MO. Effects of a seaweed-derived calcium supplement on gastric juice pH in horses. Journal of Equine Veterinary Science. 2020;91:103127.

Moore-Colyer MJS, Lumbis K, Longland A, Harris P. The effect of a marine-derived calcium supplement on gastric buffering capacity and hindgut fermentation using an in vitro equine digestion model. Journal of Equine Veterinary Science. 2014;34(6):845–851.

Boucher A, Madigan JE, Pusterla N. The equine gastrointestinal microbiome and emerging nutritional support strategies. Animals. 2024;14(3):512.

Ganda EK, Burton RJ, Leite MG, et al. Effects of Saccharomyces cerevisiae fermentation products on stress-associated changes in the equine gut microbiome. Animals. 2023;13(6):1021.

Lieb S. The effect of psyllium on sand evacuation in horses. Equine Veterinary Education. 1993;5(2):68–74.

Venner M, Lauffs S, Deegen E. Treatment of gastric lesions in horses with pectin-lecithin complexes. Equine Veterinary Journal. 1999;31(S29):91–96.

---