Did you know that at rest, a 500kg horse breathes 5 litres of air in and out with each breath and takes around 12 breaths per minute?
The amount of air moved in and out in one minute is called the minute ventilation.
Minute ventilation is calculated by multiplying the tidal volume, litres, by the respiratory rate, breaths per minute. So 5 x 12 = 60 litres per minute.
In an hour, your horse moves 3,600 litres in and out, that is around 20 bathtubs.
In 24 hours, your horse moves 86,400 litres in and out, equivalent to 34 hot tubs.
That is an extraordinary volume of air passing through the lungs every single day. But what is actually in that air?
What’s in the Air Your Horse Breathes?
- The dust in the air that comes into the stable from outside
- The dust you create from grooming or mucking out
- Dust from bedding
- Dust from forage
And can be in that dust?
- Mould spores
- Bacteria
- Pollen
- Dust mites
- Forage mites
- Sand
- Earth
Even when a stable looks clean, the air can contain far more particulate matter than we realise.
How Much Dust Is in the Stable?
A clean stable could have 50 μg or less of respirable dust, PM10 = particulate matter <10 μm in size, per m³ of air over 24 hours.
A dusty stable might have periods when the dust is 100 times higher.
Typical PM10 Levels
| Activity / Condition | PM10 (μg/m³) | Notes |
|---|---|---|
| Idle stable, quiet horse | 50–300 | Baseline, still 2–10x urban ambient air |
| Feeding, hay handling | 200–1,000 | Short bursts, organic dust dominates |
| Mucking out bedding, grooming | 500–5,000 | Peak exposure, can exceed human exposure limits in minutes |
These spikes may be brief, but when you consider how much air a horse moves in a day, the cumulative exposure becomes significant.
What Does That Mean in Real Terms?
If we assume 500 μg/m³ of dust over 24 hours:
500 μg/m³ = 500 μg per 1000 litres or 0.5 μg per litre
Over 24 hours the horse breathes 86,400 litres in and out
86,400 litres x 0.5 μg per litre = 43,200 μg of dust or 43.2 mg of dust
Now assume there is one hour around feeding, mucking out, etc when air quality is 2000 μg/m³:
In this period the horse breathes 3,600 litres
2000 μg/m³ = 2000 μg per 1000 litres or 2 μg per litre
2 μg per litre x 3600 = 7200 μg or 7.2 mg
43.2 mg + 7.2 mg = 50.4 mg of dust breathed into the lungs each day.
That is 50.4 mg of respirable dust entering the lungs every single day.
Why This Matters
Fortunately, the lung is very good at secreting mucus to help clear unwanted dust. However, depending on what makes up that dust, this can lead to allergic, irritant or sometimes infectious disease.
The challenge is that even very low-grade respiratory disease can affect performance, often without obvious signs such as coughing or nasal discharge. A horse may simply seem slightly flat, less willing, or not quite performing to its potential.
We would never expect any human athlete to live in a dusty house and then go out and compete to the best of their abilities. Yet we often expect our horses to do exactly that.
The problem may well be that we do not realise how dusty the stable environment actually is.
Top Tips to Reduce Dust Exposure
- Use the lowest dust bedding possible, straw and cheap shavings and even some expensive brands are filthy
- Never muck out with a horse in the stable
- When mucking out or laying a new bed, leave for an hour before putting a horse in
- Never groom the horse in the stable
- Ensure good ventilation at all times
- Feed soaked forage or haylage
- Dampen hard feeds
The Take Home Message
Your horse moves 86,400 litres of air through its lungs every day. What is in that air matters.
Small improvements in stable management can significantly reduce dust exposure, support respiratory health and ultimately help your horse perform at its best.
Resources
Here are some links to help you support your horses’ respiratory health!
- Animalweb Bedding Testing Results Combined!
- Vitamin C – Ascorbic Acid & Respiratory Health
- Cold Weather and Equine Respiratory Health
- Webinar – Respiratory Health Part 1 by Dr David Marlin
- Webinar – Respiratory Health – Part 2 – Respiratory Problems
- Podcast – Respiratory Problems in Horses by Dr David Marlin
