Jennifer Little BSc Hons MSc RNutr PgCert
Independent Equine Nutritionist

In horses a healthy digestive system is of utmost importance in order to support a horses health and performance. The bacterial population within a horses gut (referred to as the gut biome) are critical to its health. It is essential for both the digestive and immune systems, stimulating and adapting the immune response, providing protection against pathogens, while simultaneously sustaining digestion [1]. Any impairments or imbalances to these bacteria, can leave the horse susceptible to infections and diseases [2]. Stresses such as diet and management changes, transport and certain medications can all disrupt the gut biome [3].

Several studies have investigated the use and impact of dietary supplements and their abilities to support a horses healthy digestive system. The aim of this article is to explore the effect of three such supplements, Yeast, Fructooligosaccharides (FOS) and Mannanoligosaccharides (MOS).

Yeast has been used used for some time to support the beneficial bacterial population in the horses hindgut. There are several types of yeast, but in relation to the horse, a yeast called Saccharomyces cerevisia is the most frequently used and studied [2]. This yeast is referred to as a probiotic, in that it is a source of live, naturally occurring micro-organisms. When fed this can have a beneficial impact on the bacterial populations within the hindgut [4]. The supplementation with Saccharomyces cerevisia improves the digestibility of a horses diet by supporting the fermentation process. A process that is required to convert fibre from the diet into an available energy source for the horse. This improvement in the function of the digestive system has been attributed to this yeasts ability to modulate the bacterial populations within the hindgut [5,6,7]. A further mechanism of this yeast is that is scavenges oxygen present within the digestive tract, creating an environment more suitable for beneficial or good anaerobic bacteria [8].

A demonstrated benefit of Saccharomyces cerevisia supplementation is its influence on the lactic acid levels within the caecum and colon, the main sites of fibre digestion. It’s supplementation has been shown to increase the pH in the hindgut, and in doing so it can reduce detrimental concentrations of lactic acid [2]. This effect is even more significant in horses such as performance horses, who tend to require higher levels of starch and concentrate feeds. This need for higher starch and concentrate feeds could be due to the need to support higher work levels, higher energy requirements, late pregnancy or lactation or poor body condition. The effectiveness of supplementing with Saccharomyces cerevisia has been ascribed with mitigating of the negative effects of energy-dense diets [9].

Metabolites produced by Saccharomyces cerevisia supplementation has been shown to support the immune system, the immune cells, affect and regulate inflammatory responses in horses [2]. A combined effect that has also been shown to provide a stress-mitigating response in young horses [10].

Fructooligosaccharides (FOS) are a plant based prebiotic. Unlike yeast, prebiotics are not living micro-organisms. Rather they are a form of indigestible carbohydrates, that provides a food source for the beneficial bacteria within the hindgut. Supporting these micro-organisms with available prebiotics helps to ensure they have sufficient numbers and stability to maintain hindgut health. FOS is the most frequently used prebiotic for horses [3]. Research has demonstrated that FOS supplementation can improve fibre digestion by increasing the capacity of the bacteria within the hindgut to convert fibre into an energy source for the horse [3]. When fibre is digested more efficiently it can reduce the amount of hard feed required in order to meet that horses energy needs. However at harder work levels it maybe necessary to provide energy dense compound feeds or straights in addition to their fibre or forage sources. In this situation the inclusion of FOS has been shown to limit the negative impact of energy rich feeds on the hindgut, and to reduce the risk of colic [11].

Mannanoligosaccharides (MOS) is also a plant based prebiotic. As such MOS has no direct nutritive value to the horse itself, but provides nutrients for the bacteria within the hindgut. Its usage has been implicated in supporting optimal growth rates, health indices, reducing oxidative stress and inflammatory effects [12]. Additionally MOS supplementation has been proven to improve muscle mass, function, recovery and health [12]. It plays an important role in improving animal health and has a positive effect on its performance [13]. In relation to breeding MOS supplementation for brood mares in late gestation can increase the levels of the immune cells, IgG and IgA in the colostrum. Cells that are critical for the passive transfer of immunity from the mare to the foal. It has also been shown that MOS supplementation for mares in late gestation produced foals with an 83% reduction in the number of diarrhoea cases that required veterinary treatment [14].

The combination of yeast, FOS and MOS has been shown to improve digestibility and to create a greater capacity for resilience in the face of stresses [15]. Stresses can include transportation, increasing workload intensity, changes to daily management and forage sources, changes to routine, mixing with novel horses and even certain medications. Stresses that unfortunately can be hard to avoid and eliminate from the lifestyle of performance and competition horses. Ensuring an appropriate, balanced diet with sufficient fibre is the first critical nutritional step in supporting these horses. As the health of the hindgut and the gut biome is so critical to support the overall health and performance, providing Saccharomyces cerevisia, FOS and MOS could be a very suitable second step.


[1] Russell, S.L., Gold, M.J., Willing, B.P., Thorson, L., McNagny, K.M., Finlay, B.B., Perinatal antibiotic treatments affects microbiota, immune responses and allergic asthma. Gut Microbes 4, 158-164
[2] Perricone, V., Sandrini, S., Irshad, N., Comi, M., Lecchi, C., Savoini, G., & Agazzi, A., 2022 The role of yeast saccharomyces cerevisiae in supporting gut health in horses: An updated review on its effects on digestibility and intestinal faecal microbiota. Animals 12, 3475
[3] Bachmann, M., Glatter, M., Bochnia, M., Wensch-Dorendorf, M., Greef, J.., Breves, G., Zeyner, A. 2020 In vitro gas production from batch cultures of stomach and hindgut digesta of horses adapted to a prebiotic dose of Fructooligosaccharides and inulin. Journal of Equine Veterinary Science 90, 103020
[4] Yoon, I.K., Stern, M.D., 1995. Influence of direct fed micobials on ruminal microbial fermentation and performance of ruminants: A review. Asian-Australasian Journal of Animal Science 8, 533-555
[5] Elghandour, M.M., Chagoyan, J.C.V., Salem, A.Z., Kholif,A.E., Castaneda, J.S.M., Camacho, L.M., Buendia, G., 2014 Invitro fermentative capacity of equine faecal inocula of 9 fibrous forages in the presence of different doses of Saccharomyces cerevisiae. J. Equine Vet Sci 34, 619-625
[6] Elghandour, M.M., Mellado, M., Kholif, A.E., Salem, A.Z., Barbabosa, A., Ballinas, S., Esquivel, A., Odongo, N.E., 2016 Faecal gas production of ten common horse feeds supplemented with Saccharomyces cerevisiae. J. Equine Vet Sci 47, 1-8
[7] Elghandour, M.M., Kholif, A.E., Lopez, S., Mendoza, G.D., Odongo, N.E., Salem, A. Z., 2016 In vitro gas, methane and carbondioxide productions of high fibrous diet incubated with faecal inocula from horses in response to the supplementation with different live least additives. J. Equine Vet Sci 38, 64- 71
[8] Newbold, C.J., Wallace, R.J., McIntosh, F.M., 1996 Mode of action of the yeast Saccaromyces cerevisiae as a feed additive for ruminants Br. J. Nutr. 76, 249-261
[9] Callaway, T.R., Anderson, R.C., Edrington, T.S., Genovese, K.J., Harvey, R.B., Poole, T.L., Nisbet, D.J., 2013 Novel methods for pathogen control in livestock pre-harvest: An update. Advances in Microbial Food Safety, 1st Ed: Sofos, J., Ed., Woodhead Publishing: Cambridge, UK 1, 275-304
[10] Valigura, H.C., Leatherwood, J.L., Martines, R.E., Norton, S.A., White-Springr, S.H., Dietary supplementation of a Saccharomyces cerevisia fermentation product attenuates exercise-induced stress markers in young horses. J. Anim Sci 99, 199
[11] Geor, R.J., Harris, P.A., & Coenen, M., 2013 Equine Applied and clinical nutrition. Health welfare and performance. Saunders Elsevier, 575-576
[12] Zhao, W., Chen, L., Tan, W., Li, Y., Sun, L., Zhu, X., Wang, S., Gao, P., Zhu, C., Wang, L., Jiang, Q. 2023 Mannan Oligosaccharides promoted skeletal muscle hypertrophy through the gut microbiome and microbial metabolites in mice. Foods, 12, 357
[13] Martin, R., Chamignon, C., Mhedbbi-Hajri, N., Chain, F., Derrien, M., Escribano-Vazquez, U., Garault, P., Cotillard, A., Pham, H.P., Chervaux, C., et al 2019 The potential probiotic lactobacillys rhamnosis CNCM I-3690 Strain protects the intestinal barrier by stimulating both mucus production and cytoprotective response. Sci Rep 9, 5398
[14] Ott, E.A., Kivipelto, J., Kavazis 2002 Supplementation of broodmares with copper, zinc, iron, manganese, cobalt, iodine, and selenium Journal of Equine Veterinary Science 10, 460-464
[15] Wagner, A.L., Splan, R.K., Biddle, A.S., Girard, I.D. 2022 13 impact of biome fix on the faecal micro biome response to antibiotic challenge in horses. Journal of Equine Veterinary science 100, 103476

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