Becky James BSc MSc describes how researchers measure dust levels in the stable and most importantly- the breathing zone. 

A stable is not a natural environment for the horse, potentially exposing it to a high concentration of airborne respirable dust. The dust is composed of pollen, mould, bacteria, insects and plant fragments. If your horse spends a lot of time in the stable it is important to try to minimise exposure to this dust to avoid inducing respiratory problems.

Multiple studies have demonstrated that the level of dust within the stable is influenced by forage type, bedding material and management regime. So the activities that take place while the horse is in the stable, such as mucking out and sweeping can have a major impact. 

The choice of bedding and whether you muck out each day or do deep-litter influences the level of dust in the general environment. Dauviller et al 2018 clearly identifies, straw bedding (and dry hay feeding) as significant risk factors for Inflammatory Airway Disease and for the presence of fungal elements in equine airways.

Choosing a low-dust bedding option such as dust extracted shavings or wood pellets helps to reduce the dust generated from bedding but the addition of a sealed, padded flooring system will make a further difference. Less bedding is required, often up to 75% less and of course the less bedding, the less dust in the stable environment.

Beyond the bedding a major influence in terms of what the horse is inhaling in it’s breathing zone is the forage. 

Researchers use cyclone personal air samplers to measure the level of dust in the horse’s breathing zone. These operate by removing larger particles from the airstream using centrifugal motion before entrained smaller (respirable) particles reach the collecting filter. Particle numbers can then be counted or weighed and expressed as airborne respirable particles per litre of air.

An example of a personal cyclone air sampler. Image courtesy of Munro Instruments Ltd.

Other air samplers can measure changes in real time using a laser photometer or piezoelectric balances techniques.

Research behind these statements

Woods and colleagues demonstrated that switching from poor quality hay and straw bedding to complete pelleted feed and wood shavings as bedding reduced dust by more than 50%. Moreover, breathing zone total and respirable dust levels were reduced to 3% of that  measured under the conventional management practices.

Auger and Moore-Colyer investigated the relationship between airborne respirable dust in the breathing zone and the general stable zone when horses were kept on different management regimes, in either American barn or straight block stables. The researchers measured dust levels in 72 individual stables, measuring airborne respirable from both the stable zone and the breathing zone.

Image courtesy of the Royal Agricultural University, Cirencester, UK.

You can see in this picture how the researchers have used some familiar horse equipment to rig up the cyclone next to the horse’s nose to measure the dust in the breathing zone while the horse goes about its usual stable activities!

The lowest respirable particle concentrations for both stable designs were with shavings and Haygain steamed hay. Straw and dry hay produced the most amount of dust in both the stable zone and the breathing zone. When comparing airborne respirable dust in the breathing zone and general stable zone the dry hay and straw produced more airborne respirable dust in American barns compared with single stables indicating that neighbouring stables share dust and collectively produce higher levels of airborne respirable dust compared with when horses are in individual stables with their own space.

Choice of concentrate can also impact particulate matter exposure. Commercially available pelleted feed generated lower particulate matter concentrations by a factor of 10-12 compared to uncleaned oats, while cleaning oats or steam flaking barley effectively reduces particulate matter release by 80%. Rolled barley and oats release nearly 60 times the number of respirable particles and more than 10 times the number of Aspergillus fumigatus colony forming units when compared to commercially produced molasses‐treated concentrates.

Clements and Pirie reported that feed had a greater influence on the mean and maximum respirable dust concentration in the horse’s breathing zone than bedding. They also demonstrated a 19‐fold increase in respirable particulates in the stable whilst being cleaned, and 9‐fold increase in the respirable particulate concentration in the adjacent stable that shared airspace above the stable walls. 

Daytime total and respirable particulate concentrations have been found to be nearly double the concentrations measured overnight, independent of management system, further reinforcing the impact of activity within the barn on particulate exposures.

Whilst all of the contributing factors have an impact on the horse’s respiratory system it really is what is in the breathing zone that counts as Woods and colleagues noted:

'When ventilation rates are high approx 5 changes of air/hour (thus maximizing the chances of removing dust from the stable) the dust concentration measured in the stall grossly underestimates the breathing zone dust challenge' Woods, et al., 1993.

This suggests unless you are removing dust from the forage and therefore the breathing zone you will have limited impact on the horse, changing the source material is the only way to decrease respirable dust levels. Haygain reduces the dust from the breathing zone by 99% and therefore is an effective way of managing dust in the breathing zone of stabled 
Image courtesy of the Royal Agricultural University, Cirencester, UK.

It’s not just stables where horses are wearing cyclones, dust in the breathing zone has been measured during transportation too…..look out for an upcoming article on this!

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