Ammonia and dust in stables — what they do to horses and people
A person spends fifteen minutes a day in a box. A horse spends fifteen hours, with its head far closer to the floor, where ammonia concentrates.
Ammonia in a stable comes from urea in horse urine and concentrates just above the floor — at the nostril height of a lying horse. Up to 80% of horses show signs of mild to moderate equine asthma, and mucking out alone raises airborne dust as much as 16-fold. Three things matter: removing wet bedding quickly, choosing a material that binds ammonia, and ventilation that actually works.
If your eyes sting when you walk into the barn in the morning, ammonia has already passed the level at which airway changes begin in horses. The difficulty is that a person spends fifteen minutes a day in a box and a horse spends fifteen hours, with its head far closer to the floor. This guide gathers what the research says about air quality in stables and turns it into decisions you can actually make.
Where stable ammonia comes from
Horse urine contains urea. Urease, an enzyme present in faeces and in bedding, breaks it down to ammonia within hours — faster in warmth and damp, which is exactly what a closed box in winter provides. Ammonia is lighter than air, yet the highest concentrations in a stable are measured at floor level, because that is where it forms and where it sits when the air is still.
That explains a discrepancy that misleads many yard managers: a reading taken at head height can look acceptable while the horse lying in the box breathes air several times more concentrated.
- How much urine stays in the box — wet bedding is an ammonia factory running around the clock.
- What binds the urine — differences between bedding materials are measured in multiples, not percentages.
- How many air changes per hour — ventilation does not remove the source, but it dilutes the result.
What ammonia and dust do to the equine airway
The scale is larger than the number of visibly wheezing horses suggests. Research indicates up to 80% of horses show signs of mild to moderate equine asthma (formerly inflammatory airway disease), while the severe form — obvious coughing, laboured breathing, the classic heave line — affects 11–17% of the population.
For a competition horse, mild asthma does not mean coughing in the box. It means slower recovery after work, earlier fatigue, and a result that training cannot explain. It is one of the most frequently overlooked factors when performance drops.
| Source | What it emits | Scale |
|---|---|---|
| Urine in bedding | ammonia | highest at floor level, rising overnight |
| Hay | dust, mould spores, endotoxins | the single most common dust source in stables |
| Straw bedding | dust | 2–3× more than alternative materials |
| Mucking out | airborne particulates | up to 16× the resting level |
That 16-fold figure has one immediate organisational consequence: horses should not be standing in boxes during or straight after mucking out. The recommended gap is 30–60 minutes, which is how long particles take to settle. In practice it means reordering the day — turn out first, muck out second — which costs nothing and is among the most effective changes available.
Bedding: differences you can measure
Studies comparing bedding materials — wheat straw, wood shavings, hemp, pellets — show two things. First, straw generates two to three times more dust than the alternatives. Second, materials differ not only in absorbency but in their ability to bind ammonia: straw pellets perform best in these comparisons, limiting the conversion of nitrogen into its volatile form.
The scale of the possible improvement is large. In one study, changing bedding and forage — from straw and hay to shavings and haylage — cut airborne dust by more than 97%.
Using less bedding lowers the purchase cost and the volume removed, but it also shortens the path from urine to floor and lengthens its contact with air. If you reduce bedding, compensate by removing wet patches more often — otherwise the saving reappears as higher ammonia.
Ventilation — the most neglected element
Insulated barns sealed tight in winter “for the horses’ sake” are a textbook case of good intentions with the opposite effect. A horse tolerates cold far better than bad air; the thermal comfort of the people working in the barn is routinely mistaken for the animals’ requirement.
The effect of good ventilation is measurable. In a study using a balanced mechanical system with supply and extract, carbon dioxide, ammonia, ultrafine dust and allergens all fell together, and every horse in the study showed reduced airway inflammation.
- Natural ventilation — low inlets, ridge outlet, cross-section matched to the building volume. It works until somebody closes the inlets in winter.
- Mechanical ventilation — more expensive, but predictable and independent of wind direction and weather.
- Ventilation during work — a separate matter: open everything you can while mucking out, and bring horses back afterwards.
Not only the horses — occupational exposure
Whoever mucks out spends hours a day in the zone of highest dust concentration, usually with no respiratory protection. Organic dust from hay and bedding carries mould spores and endotoxins; chronic exposure is a recognised occupational risk factor for respiratory disease.
The minimum realistic measures: an FFP2 mask while mucking out and while handling hay, doors open during the work, and rotation so that the same person is not doing thirty boxes day after day. Vacuum systems that remove manure without it being forked and barrowed eliminate much of this exposure at source, because the dust is never thrown back into the air.
An improvement plan, cheapest first
| Action | Cost | Effect |
|---|---|---|
| Turn horses out before mucking out | none | removes exposure to the 16× dust spike |
| Open the ventilation in winter | none | lowers ammonia and CO₂ |
| Remove wet bedding daily | labour time | removes the ammonia source |
| Soak or steam hay | low | cuts the main dust source |
| Switch to ammonia-binding bedding | moderate | less ammonia and dust, smaller waste volume |
| Mechanical ventilation | high | measurable fall in airway inflammation |
| Dust-free manure removal system | high | no dust thrown up during handling |
The first three lines need no investment at all, only a change of habit and running order. Start there — if only to see how much of the problem disappears without spending anything.
Frequently asked questions
How do I know there is too much ammonia in my stable?
A noticeable smell on entering in the morning, and stinging eyes, mean the concentration is already high — the human nose only detects ammonia above levels considered safe for prolonged exposure. Measure at 30–50 cm above the floor, where a lying horse breathes, not at head height.
How many horses have respiratory problems?
Research indicates up to 80% of horses show signs of mild to moderate equine asthma, and 11–17% suffer from the severe form. The mild form usually does not produce coughing in the box; it shows up as reduced performance and slower recovery after work.
Can horses stay in their boxes during mucking out?
It is not advisable. Mucking out raises airborne dust by as much as 16 times the resting level. Horses should be out for 30–60 minutes while particles settle.
Which bedding is best for the equine airway?
Straw produces two to three times more dust than alternative materials. In comparisons of ammonia binding, straw pellets perform best. Wood shavings are a reasonable compromise between price, dust and absorbency. How often wet material is removed still matters more than the choice of material.
Is a warm, sealed barn better for horses in winter?
Usually not. Horses tolerate low temperatures far better than poor air quality. Closing ventilation in winter raises ammonia, carbon dioxide and dust. The priority is air exchange without draughts at horse level, not keeping the temperature above freezing.
This guide is informational and does not replace veterinary advice. If a horse shows signs of respiratory disease — coughing, nasal discharge, exercise intolerance — veterinary diagnosis is required.
Sources
- Air Quality in Horse Barns: Respiratory Health, Dust & Ventilation — Mad Barn
- Dust and ammonia in horse stalls with different ventilation rates and bedding — Aerobiologia
- Air Quality in Horse Stables — IntechOpen
Last updated: 2026-09-20. Prepared by the team at Clever Equine Solutions sp. z o.o..