Coming soon · Humequine
The Microbiome Management Guide
Equine Edition
Why lasting digestive health begins with the environment inside the gut. A short introduction for horse owners, trainers and barn managers.
Microbiome Management in horses
From forage to the living world within.
A horse at grass is eating mostly fibre, and much of it the horse cannot break down alone. Microbes in its hindgut ferment that forage, in a caecum that holds about three times the volume of its stomach.
Seen and unseen
A horse at grass, and the fermentation world inside it.
A horse at grass, and the hindgut behind its ribs: a caecum of 27 to 30 litres against a stomach of 8 to 10, and the large colon, where microbes break down the fibre the horse eats.3
Environmental conditions
Resources, physical conditions and management.
Microbial activity
Functions and interactions within the community.
Observable function
What can be measured in the host or wider system.
The large colon
- a Large colon wall
- b Plant fibre
- c Bacteria
- d Mucus layer
Observable function Manure consistency and body condition score
- Manure consistency and body condition score
Why this system is investigated. The hindgut is a fermentation environment the horse depends on, and anything added to feed meets those microbes before it meets the horse.
That raises an equine question of its own: whether a humic or fulvic preparation is used by particular hindgut microbes, or acts on their environment another way, and what an owner would then see in manure, appetite and condition. This library holds no study of a humic or fulvic material in horses, so the work starts from a baseline.
Why the setting matters
Forage first, then the hindgut.
Pasture or hay should make up most of what a horse eats: for most mature horses at least 1 percent, and ideally 1.5 to 2.5 percent, of body weight in forage each day.1 The horse relies on microbes in its hindgut to process that forage, which is why horses are called hindgut fermenters. What the horse eats is also what those microbes live on.1,3
Grazed
Pasture
Fresh grasses and legumes, eaten where they grow.
Harvested
Hay
Forage cut, dried and stored, fed when grazing is short or unavailable.
Conserved
Haylage
Another stored forage. The equine study below compared ponies kept on hay or on haylage for years.5
Into the horse.
Simplified equine digestive anatomy. Caecum and stomach drawn to the Merck volumes; the rest not to scale.3
- 1
Stomach
Small for the animal: about 8 to 10 litres.
- 2
Small intestine
A major site of enzymatic digestion and nutrient absorption.
- 3
Caecum
About 27 to 30 litres, part of the hindgut’s microbial fermentation environment.
- 4
Large colon
A major region of continued fermentation and absorption.
- 5
Small colon and rectum
The later passage of digestive contents toward elimination.
The hindgut is important, but it is one part of the digestive system. What leaves the horse as manure has passed through every compartment, so it cannot give a complete picture of any one of them.
What is happening here
Look for function and adaptation over time.
Within the equine framework, Digestive Stability describes appropriate digestive function and the capacity to adapt through change.
The focus is the individual horse’s pattern over time, considered alongside feeding, management and professional assessment.
Function
What is usual for this horse, and which observations deserve attention?
Adaptation
How do observations change through a transition in feeding, routine or circumstances?
Recovery
Following a disruption and any necessary care, does function move back toward the horse’s usual pattern?
Digestive Stability is a working concept within the framework. It is not a diagnosis, a guarantee of symptom-free health or evidence that the microbial community has remained unchanged.
Applied to one change: winter hay to spring grass.
Digestive environment
The forage changes from hay to fresh pasture, introduced gradually, with turnout time recorded.
Microbial activity
Not visible from the yard. Research measures it by sampling, as in the forage study below.
Horse-level observations
Appetite, water, manure and body condition, against this horse’s own baseline.
What an owner can follow
Follow the horse through a change, not a single sign.
You have to know what is normal for a horse before you can recognise what is not.6 A simple record, kept the same way before, during and after a change in feeding or routine, gives the horse’s own baseline to compare against.
- 1
Before: the baseline
For a period before any change, note forage and feed, turnout and work, appetite, water, manure and body condition, the same way each day. This is what normal looks like for this horse.6
- 2
The change
Write down what changed and when. Feed changes are best made gradually: replacing 20 to 25 percent of the current hay or grain every other day, so a full change takes a week or more and the hindgut microbes have time to adjust.1
- 3
The weeks after
Keep the same observations, recorded the same way, so that a difference reflects the horse rather than a new way of looking.
- 4
What else changed
Travel, competition, housing, weather, dental or veterinary care and other supplements. Any of them can coincide with a feeding change, and each belongs in the record.
What manure and coat can, and cannot, tell you.
- They can show
- Whether this horse is departing from its own pattern, and when it started, which is exactly what to bring to a veterinarian.
- They cannot show
- Which microbes are present or what they are doing. Loose manure, for example, can follow a sudden change in feed, nervousness, irritation in the gut or, in mares, heat cycles.6 A coat has many influences too. Measuring the microbes takes laboratory sampling.
Observation does not replace veterinary assessment. Contact your veterinarian promptly for suspected colic, significant diarrhoea, reduced appetite or other concerning changes. Do not wait for a supplement trial to assess an unwell horse.6
What is established, and what is being investigated
Equine research and next questions.
What is known about the horse’s hindgut comes from equine research on forage, anatomy and microbes. What a humic or fulvic material does in a horse is a separate question, with its own evidence to find.
Forage type was associated with different urinary metabolites and some bacterial groups.
Research involving 20 Welsh Mountain ponies examined hay and haylage feeding. The investigators reported clear differences in urinary metabolites, and differences in some faecal bacterial groups but not in faecal bacterial diversity.
Limitation. One group of ten ponies per forage, so forage is confounded with group, pens, paddocks and grass source; forage composition was not reported.
Funding. The Laminitis Trust via Equi Life Ltd, which the corresponding author owns.
Interpretation. The work illustrates why feeding context matters when examining microbial observations. It did not test a humic or fulvic preparation or establish a universal target microbiome for horses.
- Study design
- Longitudinal study of two forage groups established five years earlier
- Material
- No humic or fulvic material tested; long-term feeding of hay or haylage, with summer grazing
- Source
- Leng et al., 2022. Hay versus haylage: Forage type influences the equine urinary metabonome and faecal microbiota
In this collection. One background record for horses, and no study of a humic or fulvic material in a horse.
The questions an equine study of these materials would need to settle.
Findings from soil, poultry or trout do not answer the equine question; the horse’s hindgut is its own environment.
What was administered?
Identify the preparation, composition, route and study exposure.
What was measured?
Distinguish digestive observations, microbial measurements and other outcomes.
What explains the response?
Consider whether the design can separate the preparation’s effect from diet, management and other influences.
Forage already supplies substrates for hindgut fermentation. Whether an additional preparation is directly used by particular microbes, or influences the environment through another interaction, requires its own evidence.
For practitioners: what to record
What to document about a horse’s feeding, routine and digestive observations, so that a change can be read in context.
A useful observation includes what changed around the horse.
When reviewing digestive function, document the feeding program, routine and recent transitions. This context helps frame the question before attributing a change to a particular cause.
Forage and feeding
Record forage type and batch, pasture access, concentrates, supplements and feeding pattern.
Travel and routine
Record transport, competitions, changes in turnout, housing and daily schedule.
Life stage and individual needs
Consider age, workload, body condition and relevant dental or veterinary history.
Care and concurrent changes
Record treatments, professional recommendations and other changes that occurred during the observation period.
These are areas to document, not a checklist for diagnosing the cause of a digestive concern.
Know the horse’s baseline. Record the context.
Consistent observations can support a more useful discussion with the people responsible for the horse’s care. Record what changed, when it changed and what else was happening.
| Area | What to document |
|---|---|
| Feeding | Forage, pasture, concentrates, supplements and recent changes. |
| Appetite and water | Changes from the horse’s usual pattern, distinguishing observation from measured intake. |
| Manure | Consistency, frequency and any separately observed liquid, recorded consistently. |
| Body condition | Trends using an appropriate, consistent assessment method, with hands on the horse rather than by eye from a distance. |
| Routine | Travel, exercise, turnout, housing and schedule changes. |
| Care | Veterinary assessment, treatments and other concurrent interventions. |
Where to learn or contribute
The horse publications.
Bring equine expertise to the work.
Review a publication, interpret a record, or help design the baseline observations an equine study of these materials would need. This collection holds none yet.
Associated brand. Humequine, run by the project’s founders, sells products for horses. No study on this page tested a Humequine product.
How the project relates to its brandsSources and further reading
- Hathaway M, Catalano D. Ten things you should know about feeding the mature horse. University of Minnesota Extension. Reviewed 2021. extension.umn.edu/agriculture/animals-and-livestock/horse/ten-things-you-should-know-about-feeding-the-mature-horseForage as most of the diet and how much; hindgut fermentation; changing feeds gradually; body condition.
- Martinson K, McIntosh B. Using hay in horse diets. University of Minnesota Extension. Reviewed 2023. extension.umn.edu/agriculture/animals-and-livestock/horse/hay-in-horse-dietsForage-based digestive context.
- Easley J. Introduction to digestive disorders of horses. Merck Veterinary Manual, horse owners. Reviewed 2019. www.merckvetmanual.com/horse-owners/digestive-disorders-of-horses/introduction-to-digestive-disorders-of-horsesOrder of the digestive tract, and the relative capacity of the stomach and cecum used in the schematic.
- University of Surrey. Influence of forage type on gut microbiome. www.surrey.ac.uk/research-projects/influence-forage-type-gut-microbiomeProject page for the forage study.
- Leng J, McNally S, Walton G, et al. Hay versus haylage: forage type influences the equine urinary metabonome and faecal microbiota. Equine Veterinary Journal 54:614 to 625. 2022. doi.org/10.1111/evj.13456The forage study summarised in the evidence library.
- Malone E. Basic first aid for your horse and preparing for emergencies. University of Minnesota Extension. Reviewed 2021. extension.umn.edu/agriculture/animals-and-livestock/horse/basic-horse-first-aid-and-preparing-for-emergenciesKnowing what is normal; what loose manure can follow; when to call a veterinarian.
Prepared by Carbon Biome Project, 19 October 2026; revised 22 October 2026. External scientific review of this page has not been completed. Citing the University of Minnesota, the University of Surrey and the Merck Veterinary Manual does not imply their endorsement of the project.