A horse's digestive system relies heavily on what happens in the cecum and large intestine. These sections of the digestive tract are home to a diverse community of microorganisms that break down plant fibres the horse cannot digest using its own enzymes. During this process, short-chain fatty acids are produced, providing an important source of energy for the horse.
New research published in 2026 offers further insight into the close relationship between equine nutrition and the composition of the gut microbiome.
Studies have found differences in the microbial communities of grazing and stable-fed horses. They have also demonstrated that fibre-based and starch-based diets can influence the composition of the faecal microbiota within just three weeks.
What do these findings mean in practice, and how can they help us better understand horse nutrition?
Grazing horses had more fibre-degrading bacteria
A study published in Frontiers in Microbiology in July 2026 investigated the relationships between breed, feeding management, geographical location and the equine gut microbiome.
Researchers analysed faecal samples from 139 horses, including Thoroughbreds, Mongolian horses, Warmbloods and Thoroughbred–Mongolian crossbred horses.
Some horses were kept in stables, while others were managed on pasture. Microbial communities were analysed using 16S rRNA gene sequencing.
What did the researchers discover?
One of the most interesting findings came from comparisons between horses of the same crossbred genetic background, some of which were grazing while others were stable-fed.
Grazing horses had higher relative abundances of certain bacterial groups associated with fibre degradation, particularly bacteria belonging to the genera Ruminococcus and Fibrobacter.
Fibrobacter is known for its ability to degrade cellulose, while the Ruminococcus genus also includes important microorganisms involved in breaking down plant fibres.
The researchers observed that grazing horses had microbial communities with a composition strongly associated with the utilisation of complex plant fibres.
Breed accounted for approximately 44.8% of the observed variation in microbial community composition. Feeding management accounted for approximately 10.3%, while geographical location explained around 2.7%.
Genetic background therefore showed a substantial association with the composition of the gut microbiome, but feeding management also had an independent statistical association with microbial differences.
However, grazing and stable management often differ in several environmental and management factors. The observed bacterial differences cannot therefore be attributed solely to the amount of fibre consumed.
The study highlights the complex relationship between a horse's environment, feeding management, individual characteristics and gut microbial communities.
Fibre vs starch – differences in the microbiome after just three weeks
Another study published in 2026 investigated the effects of dietary composition under more controlled conditions.
Published in the Journal of Equine Veterinary Science, the study involved 30 Quarter Horses approximately 16 months of age.
The horses were divided into two dietary groups:
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One group received a fibre-based concentrate.
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The other group received a concentrate containing more starch.
The diets were formulated to provide comparable amounts of energy and protein. The study lasted 24 days, with faecal microbiota analysed at the beginning and again on day 21.
How did the gut microbiome respond?
After three weeks, differences were observed in the composition of the faecal microbiota between the two groups.
In horses receiving the fibre-based concentrate, the relative abundance of bacteria belonging to the Lactobacillaceae family was approximately 5.7%, compared with 2.4% in the starch-fed group.
The starch-fed horses, on the other hand, had a higher relative abundance of Lachnospiraceae bacteria, approximately 38%, compared with 32% in the fibre-fed group.
These bacterial families contain different microorganisms with varying metabolic functions. A higher proportion of any particular bacterial group does not automatically indicate better or worse digestive health.
The important finding was that different dietary carbohydrate sources were associated with measurable changes in microbial community composition within 21 days.
The equine gut microbiome is therefore not a fixed system. It continuously adapts to the nutrients available in the diet.
Dietary starch did not worsen the exercise-induced inflammatory response
The researchers also investigated whether the carbohydrate composition of the diet influenced the inflammatory response to exercise.
The horses performed a two-hour submaximal exercise test, during which several blood inflammatory markers were monitored.
The researchers initially hypothesised that a starch-based diet might intensify the inflammatory response associated with exercise.
The findings did not support this hypothesis.
Diet alone did not increase the measured inflammatory markers before exercise.
However, differences in the inflammatory responses were observed between the dietary groups following exercise. For some measurements, the fibre-fed horses showed a stronger or more prolonged response than the starch-fed horses.
The researchers suggested that horses receiving the fibre-based diet may have experienced a greater acute inflammatory response during exercise.
This does not mean that fibre is harmful or that starch is automatically beneficial.
The study involved young horses receiving moderate amounts of starch. Its findings cannot be directly applied to horses with metabolic disorders, laminitis susceptibility or other specific dietary needs.
Instead, the study demonstrates an important principle:
The effects of a diet cannot be evaluated simply by categorising nutrients as good or bad. The overall composition of the diet matters.
Why is fibre so important for equine digestion?
Horses have evolved to consume fibre-rich plant material throughout much of the day.
Structural carbohydrates found in forage, including cellulose and hemicellulose, pass largely undigested through the small intestine before reaching the cecum and large intestine, where microorganisms break them down through fermentation.
This process produces short-chain fatty acids, including acetate, propionate and butyrate.
These compounds provide a significant proportion of the horse's daily energy supply.
Fibre is therefore much more than bulk in the diet.
It is an important source of energy for the horse and a major source of nutrients for the microorganisms living in its hindgut.
However, the extent to which different fibres can be utilised depends on their structure, digestibility and the microbial community present in the digestive tract.
For a more detailed explanation, read our article on Understanding the Horse's Large Intestine.
The gut microbiome needs time to adapt to dietary changes
Because the gut microbiome responds to dietary composition, the way feeding changes are introduced is important.
When a new batch of hay is introduced, the grazing season begins or ends, or the composition of concentrate feed changes, the nutrients available to intestinal microorganisms also change.
Sudden and substantial changes in starch intake, in particular, can affect hindgut fermentation and microbial activity.
New feeds should therefore be introduced gradually. A transition period of approximately 1–2 weeks is generally advisable, while horses with sensitive digestive systems or those undergoing major dietary changes may require a longer adjustment period.
The 2026 studies demonstrate associations between feeding practices and the microbiome, as well as differences following a 21-day feeding period. However, they do not establish an exact adaptation period suitable for every horse.
In practical feeding management, the most important principles include:
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Providing sufficient quantities of good-quality forage
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Maintaining a consistent feeding routine
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Introducing new feeds gradually
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Considering total starch intake and the amount fed per meal
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Ensuring adequate access to clean drinking water
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Adjusting the diet to the horse's individual energy requirements and health status
In addition to forage quantity, its nutritional composition should also be considered.
Not all dietary fibres are the same
Fibre is often discussed as a single nutritional component, even though different fibres can have very different properties.
Structural fibres found in plant cell walls, including cellulose and hemicellulose, are essential components of forage-based diets.
Other fibre-rich and fermentable carbohydrates differ in their solubility, water-holding capacity and availability to intestinal microorganisms.
For example:
Chia seeds contain both insoluble and water-binding fibres. When mixed with water, they develop their characteristic gel-like texture.
Psyllium is particularly well known for its high water-holding capacity. Its gel-forming fibres behave differently in the digestive tract from the structural fibres found in hay.
Inulin is a fermentable fructan that can be utilised by intestinal microorganisms. It is among the compounds studied for their potential prebiotic properties.
Different fibre sources should therefore not be considered identical or automatically interchangeable.
It is also important to remember that no individual fibre supplement can replace sufficient quantities of good-quality forage.
What does the research tell us about fibre-based feed supplements?
The 2026 studies did not investigate Chia de Gracia products, and their results cannot be used to claim that any particular supplement produces the same microbial changes observed in the research.
However, the findings provide further insight into how dietary carbohydrate composition is associated with the environment in which intestinal microorganisms live.
Chia de Gracia offers a selection of fibre-rich ingredients and complementary feeds that can be included as part of an individually balanced equine diet.
Chia – fibre and fatty acids for the daily diet
Chia seeds for horses provide dietary fibre, plant protein and naturally occurring omega-3 fatty acids, particularly alpha-linolenic acid (ALA).
One of the distinctive properties of chia is its water-binding fibre, which forms a gel-like texture when mixed with liquid.
Chia can be included as a complementary ingredient alongside the horse's regular forage-based diet.
Gastro Clay B – inulin and yeast
Gastro Clay B is a complementary feed containing ingredients such as inulin, brewer's yeast, bentonite and live Saccharomyces cerevisiae CNCM I-1077 yeast.
Inulin is a fermentable carbohydrate that can be utilised by intestinal microorganisms.
The Saccharomyces cerevisiae CNCM I-1077 strain is authorised in the EU as a zootechnical feed additive for horses for the stabilisation of gut flora.
It is important to distinguish between the dietary interventions investigated in the 2026 studies and research examining the effects of specific yeast strains.
Neither of the two studies discussed in this article investigated Gastro Clay B or the effects of this particular yeast strain.
Complementary feeds should always be selected according to the horse's overall diet and individual nutritional requirements.
What are the key takeaways from the 2026 studies?
Perhaps the most interesting finding is not the name of an individual bacterial species or its relative abundance in the gut.
The more important message is that the equine gut microbiome is a complex and dynamic ecosystem influenced by diet, genetics and environmental conditions.
The 2026 studies demonstrated that:
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Grazing horses had higher relative abundances of certain fibre-degrading bacterial groups than stable-fed horses of the same crossbred genetic background.
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Breed was one of the major factors associated with microbial composition, while feeding management also showed an independent association.
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Horses receiving fibre-based and starch-based concentrates had different microbial community compositions after 21 days.
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Changes in microbial composition did not automatically indicate a harmful inflammatory response.
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Dietary effects should be interpreted in the context of the complete diet rather than individual bacterial groups.
These studies do not identify a single ideal feeding programme for all horses.
Instead, they improve our understanding of how closely diet and gut microbial communities are connected.
Good equine nutrition still begins with sufficient good-quality forage, appropriate energy intake and carefully managed feeding changes.
Complementary feeds can be used to support a balanced feeding programme, but they cannot replace its foundation.
References and further reading
1. Differential shaping of equine gut microbiota structure and function by breed and feeding regimen (2026).
Frontiers in Microbiology.
A study analysing faecal samples from 139 horses and investigating associations between breed, feeding management, geographical location and microbial community composition.
https://doi.org/10.3389/fmicb.2026.1852554
2. DiSilvestro, A. N., Wesolowski, L. T., Williams, B. D., Warren, L. K., Athrey, G. & White-Springer, S. H. (2026).
Short-term provision of moderate dietary starch alters fecal microbiota but does not exacerbate exercise-induced inflammation in yearling Quarter Horses.
Journal of Equine Veterinary Science, 166, 106071.
The study compared fibre-based and starch-based concentrate diets and their associations with the faecal microbiome and exercise-induced inflammatory responses.
https://doi.org/10.1016/j.jevs.2026.106071
3. National Research Council (2007).
Nutrient Requirements of Horses, 6th Revised Edition. National Academies Press.
A comprehensive scientific reference covering equine nutrition, fibre digestion and feeding requirements.
https://doi.org/10.17226/11653
