How the equine microbiome influences behaviour, focus and performance
For years, equine science focused primarily on the musculoskeletal system, specifically tendons, joints, muscles, and conditioning. However, recent research has shifted attention inward, to a system less visible yet, it emerges, equally vital to performance: the gut.
The so-called gut–brain axis, the constant communication between the digestive tract and the central nervous system, is now recognised as one of the most powerful regulators of equine mood, focus, and even trainability.
The gut as a ‘second brain’
The horse’s digestive system contains an estimated 100 trillion microorganisms, including bacteria, yeasts, and protozoa. These are collectively known as the microbiome. This ecosystem ferments fibre, produces essential nutrients, and maintains immune health.
Fascinatingly, though, it also produces chemical messengers such as serotonin, dopamine, and short-chain fatty acids that directly affect the horse’s nervous system. When the gut is inflamed or imbalanced, those communication signals can alter behaviour, making a normally calm horse edgy, reactive, or unfocused.
NOTE: The vagus nerve also plays a role in this communication between gut and brain, serving as its main information highway, continuously sending messages between the intestines and the brain.
Did you know?
Around 90% of the body’s serotonin is produced in the gut. The microbiome influences tryptophan metabolism, which directly affects the production of serotonin – one of the body’s key neurotransmitters for mood regulation. In horses, just as in humans, serotonin doesn’t only affect happiness; it plays a role in patience, trainability, and response to pressure. An imbalanced gut can skew this system, meaning that shifts in microbial composition can alter mood and reactivity from the inside out.
Signs that something’s out of balance
Early indicators of gut dysbiosis (microbial imbalance) may include:
- Poor appetite or weight loss despite adequate feed
- Loose or inconsistent droppings
- Girthiness, resentment of grooming, or sensitivity along the flanks
- Mood swings, spooking, or ‘explosive’ reactions under saddle
- Dull coat or chronic low-grade colic
What’s fascinating is how quickly behaviour can shift once the gut environment is restored. Researchers have documented calmer demeanours and better recovery rates in horses whose microbiota have been supported through diet and management.
Competition horses live lives full of potential stressors: travel, changes in routine, high-energy diets, and too much time in the stable. Each of these can disrupt the delicate microbial balance of the hindgut.
When that happens, harmful bacteria can release toxins that damage the intestinal lining, triggering inflammation and allowing endotoxins to leak into the bloodstream – a process known as leaky gut. These inflammatory molecules can influence the brain, heightening anxiety and reducing mental clarity.
Studies in both humans and animals show that systemic inflammation can impair decision-making, focus, and stress control, which are all critical traits in an athlete that must perform under pressure.
Short-chain fatty acids (SCFAs)
Beneficial gut bacteria produce short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate – tiny but powerful compounds that serve as an essential fuel source for the intestinal lining. These metabolites help maintain the integrity of the gut barrier, reducing inflammation and preventing harmful substances from leaking into the bloodstream. When that barrier is intact, the horse’s immune and nervous systems remain stable; when it falters, systemic inflammation can ripple outward, subtly altering energy levels, focus, and even temperament.
Feeding for a healthier mind
Supporting the gut–brain axis starts in the feed room. The equine gut evolved for constant, low-starch grazing, yet modern feeding practices often rely on large, high-energy meals. This mismatch disrupts the microbial community and, by extension, the horse’s mental balance.
Fibre is the cornerstone of equine health; without enough long-stem roughage, the microbial community begins to collapse. Horses evolved to graze for 16–18 hours a day, and long gaps without forage can create acid spikes and microbial die-off.
Feeds high in non-structural carbohydrates (NSC) – starch and sugars – trigger spikes in blood glucose and the stress hormone cortisol, lowering microbial diversity and increasing hindgut acidity. Over time, this can make horses more reactive, less focused, and slower to recover from stress.
By contrast, continuous access to forage stabilises pH and supports the microbes that produce SCFAs, fostering calmness and consistency. Long-stem roughage, multiple hay types, and slow-feeding systems mimic the horse’s natural grazing rhythm, keeping digestion and mood steady.
Consistency is also key in feeding. Even a change in hay type can shift the microbiome within 24–48 hours, sometimes leading to transient colic or behavioural changes. Any feed alteration should be made gradually over at least a week.
Hydration also plays a vital role. Electrolyte imbalances and dehydration slow gut motility and fermentation, which can cause both physical discomfort and mental restlessness. Ensuring access to fresh water, free-choice salt, and proper electrolyte supplementation during travel or competition supports both gut and brain performance.
Prebiotics (such as yeast cell wall extracts and inulin) feed beneficial bacteria, while probiotics supply living strains of those bacteria directly. Emerging interest also surrounds postbiotics, which are the beneficial metabolites produced by microbes, such as butyrate, which helps reduce inflammation and strengthen the gut lining.
Equally important are management factors: consistent turnout, reduced travel stress, gradual feed changes, and slow feeding systems that mimic natural grazing patterns.
For performance horses, nutritional strategies that stabilise the microbiome – such as buffer supplementation, low-starch diets, and the use of specific yeast cultures – can have measurable behavioural benefits. Riders often report improvements in rideability, relaxation, and focus.
Feeding for the mind
Do:
1. Provide ad-lib or constant access to good-quality forage.
2. Use slow-feed haynets or multiple hay stations to mimic natural grazing.
3. Choose low-NSC feeds (starch + sugar below 12%).
4. Introduce new feeds gradually over seven to ten days.
5. Offer plain salt and clean water at all times, especially during travel or after work.
Don’t:
1. Feed large concentrate meals (over 2 kg per serving).
2. Make abrupt feed or hay changes.
3. Restrict forage for weight control without professional guidance.
4. Ignore subtle signs of gut stress, e.g. girthiness, loose droppings, mood changes, or loss of focus.
Beyond feed
The gut-brain connection also reminds us that stress works both ways. Chronic anxiety, inconsistent handling, or lack of turnout can alter gut motility and microbial diversity. Calm, consistent environments support digestive health just as much as good feed.
In this sense, ‘training the brain’ also means ‘caring for the gut.’ Techniques that promote relaxation – from long, low warm-ups to predictable routines – help lower cortisol levels, allowing the gut to function more efficiently. This results in a horse who not only feels better but thinks better.
Did you know?
Poor microbial diversity can compromise nutrient absorption, leading to energy fluctuations, muscle fatigue, and reduced mental sharpness. A horse that seems dull, distracted, or overly reactive may simply be lacking the metabolic support it needs for calm focus.
Diagnostics
While microbiome science is still emerging, it’s already beginning to reshape equine sports medicine.
Faecal microbiome testing is now available through a few pioneering laboratories, such as EquiBiome in the UK. These tests analyse the bacterial DNA present in a sample, offering a snapshot of gut diversity and identifying imbalances that may be linked to metabolic stress, poor condition, or reactivity.
Veterinarians are also using blood inflammatory markers, including serum amyloid A (SAA) and fibrinogen, as indirect indicators of gut stress. Elevated levels can suggest chronic inflammation, often correlating with changes in behaviour, energy, and performance consistency.
In addition, some equine sports medicine practices are introducing gut health scorecards, which combine observation (coat, droppings, appetite, demeanour) with laboratory data. These integrated assessments give riders and vets an early warning system before small imbalances become performance-limiting issues.
While equine microbiome testing remains in its infancy, early results are promising – helping veterinarians identify patterns of bacterial diversity linked to resilience, focus, and recovery.
Looking ahead
The science of the equine microbiome is still evolving, but its implications are far-reaching. In the future, microbiota testing may become part of the pre-purchase exam or be used to guide dietary or management decisions with precision. Already, researchers are exploring microbial ‘fingerprint’ associated with calmness, athleticism, and stress resilience.
For now, what we know is simple but quite profound: when we nurture the gut, we nurture the mind; ultimately, the horse’s digestive and nervous systems are not separate entities but work together to create happy, healthy horses.