Respiratory problems are a common occurrence in horses, sometimes they occur in acute (short-term) bouts or can be chronic illnesses. Some respiratory diseases are communicable to other horses, while others are not contagious and occur due to allergies or environmental factors.

Horses with an acute respiratory illness, such as equine influenza, may recover without complications. Horses with chronic respiratory conditions, such as equine asthma, can continue to have symptoms that, if not managed, may worsen over time.

Because many horses are kept in a stall for part, or most of the day, barn ventilation is paramount to reducing the risk of respiratory disease. Airborne dust, noxious gases, and infectious agents can negatively impact or even put an end to a horse’s athletic career. [1]

When horses inhale, air enters the nostrils, the trachea, and then travels to the bronchi and bronchioles of the lungs. Gas exchange occurs in the alveolar sacs. There, cells called macrophages engulf respirable particles, including dust and bacteria.

A large amount of dust or poor air quality can decrease the ability of macrophages to fight infectious agents. [1] This article will discuss the importance of air quality in horse stables and suggest approaches to improve ventilation to support equine respiratory health.

Equine Respiratory Issues

The most common equine respiratory disease is equine asthma, formerly known as heaves, recurrent airway obstruction, equine COPD or inflammatory airway disease.

Equine asthma encompasses inflammatory diseases of the lower airway in horses. It involves a complex interaction between environmental and genetic factors that researchers don’t completely understand.  Exposure to inhaled dust and mold is known to play an important role in the development of the disease. [2][3][4]

Equine asthma is similar to both allergic and non-allergic asthma in people. However, the condition in horses is the direct result of environmental exposures. [3] There are several types of equine asthma (including early vs. late onset and allergic vs. non-allergic) and varying degrees of severity. [3]

Equine asthma can be categorized as mild, moderate, or severe. Mild to moderate asthma can affect horses of any age, while severe asthma is usually only seen in horses over age seven. Studies show up to 80% of horses may suffer from mild to moderate equine asthma, while only 11-17% of horses may be affected with severe asthma. [4]

Signs of Equine Asthma

Symptoms of equine asthma may be difficult to detect at first. The most reliable indicator, however, is coughing — even if it is infrequent. [4]

As the disease progresses, other signs may include:

  • Nasal discharge
  • Increased recovery time
  • Reduced performance
  • Exercise intolerance
  • Difficulty breathing at rest (with severe asthma) [3][4]

Medications can be administered to affected horses through a mask known as a nebulizer. [5]  The good news is that when horses with mild to moderate asthma are removed from environments that contain triggering airborne agents, their clinical signs and underlying airway inflammation often resolve. [3]

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Air Quality and Dust in Barns

Air quality in the barn can greatly affect your horse’s respiratory health, leading to conditions such as equine asthma. Airborne dust comprises particulates from soil, mould, bacteria, insect and mite fragments, hair, manure, plant material, and more.

Dust particles are classified based on size and penetration into human airways:

  • Total dust represents all dust particles. It is composed of dust that can be physically cleaned from barns.
  • Inhalable dust particles can be breathed into the mouth or nose.
  • Thoracic dust refers to slightly smaller particles than inhalable dust and can reach the upper portion of human airways.
  • Respirable dust can reach the deepest airways. It is small enough to not be trapped by natural clearance mechanisms like mucus. Respirable dust is thought to be important in common lower airway diseases of horses.
  • Ultrafine dust is so small that it is thought to pass into the bloodstream and lead to problems elsewhere in the body. However, this size of dust particle has not been thoroughly studied.

While these size classifications are based on human research, they can also be applied to equine health. Combinations of total, inhalable, thoracic, and respirable dust are often measured when studying horse facilities. [6]

Factors Affecting Air Quality

There are a number of different factors in the barn that can impact equine respiratory health. The following factors are the most important:

Hay Quality & Storage

The most common source of dust and mould is hay. Hay with visible dust or mould should never be fed, but even good-quality hay contains some dust and mould. [1] Hay also contains fungi, bacterial endotoxins, and other allergens that can adversely affect a horse’s respiratory health. [3]

Horses fed inside a closed barn where hay is stored are exposed to more dust and mould, which may be inhaled. Because of this, hay should be stored as far away from stalls as possible.

Storing hay in a loft above stalls may be convenient, but it also results in a constant source of dust. If a separate storage trailer or building is available, that is the best option for hay storage. [6]

Avoid feeding round bales indoors or to horses with respiratory problems, as they can harbour more dust and mould than square bales. [8]

Feeding Position

How and where hay is fed can also affect a horse’s respiratory health. Feeding hay at ground level will reduce the amount of dust the horse inhales. When a horse eats with a head-down position, this also helps with the clearance of any dust or other particles they do inhale. [6]

By contrast, feeding hay from a raised net or rack has been shown to increase the amount of inhaled dust and other particles. [6]

Soaking & Steaming Hay

To further decrease dust in hay, owners can steam or soak hay before feeding. Soaking or steaming hay is recommended for horses with equine asthma symptoms but can also be used as a preventative measure to promote respiratory health. [6][7][8]

Even sprinkling hay with water can reduce the amount of dust. [6][7][8]


One alternative to hay is haylage, which is fermented and made from grass cut at an earlier stage than hay. Once cut and dried, haylage is wrapped in plastic and retains its original nutrients.

One study showed that changing a horse’s diet and bedding from hay and straw to haylage and shavings reduced dust levels by more than 97%. [6]

Stall Bedding

Stall bedding is the second most important factor affecting a horse’s respiratory health if they are kept stalled part of full time. Being outdoors is best for horses, but this isn’t always feasible with boarding situations.

If a horse must be stalled, it’s important to choose a bedding material with low dust levels to reduce the risk of equine asthma or other respiratory problems.

The main function of stall bedding is to absorb moisture and promote a healthy environment for your horse in the barn. Bedding material is also important of the horse’s comfort and allows them to engage in natural behaviors such as lying down to sleep. [9]

The most common materials used for stall bedding include wood shavings, sawdust, straw, and peat. Other less commonly used materials used include pelleted wooden materials, pelleted straw from different plants, shredded paper, shredded plant material, and wood chips. Each of these have advantages and disadvantages. [10]

Studies show that straw bedding is not the best option as it can produce dust levels two or three times that of alternative bedding materials. Straw also contains higher levels of endotoxin contamination. [9] If using straw bedding, select dust-free straw.

Peat has been found to contain less dust than some other bedding materials. Studies show that horses have less airway inflammation with peat compared to wood shavings. Owners should keep in mind that the hygienic quality and dust levels in peat may be unpredictable. [2]

Using low-dust stall bedding is important, but it’s important to understand that other factors associated with bedding can also negatively impact a horse’s respiratory health. Mold, viruses, bacteria, pores, allergens, and endotoxins can also originate from bedding.


High ammonia levels in a barn can put the horse’s airways at risk and increase mucus production. [1] Ammonia originates from decomposed urine in stall bedding and becomes a noxious gas. It has a distinct smell that horse owners can likely recognize when they walk into a horse’s stall.

When horses lie down, they are more exposed to ammonia. Likewise, ponies and foals whose breathing zone is closer to the ground will have more exposure to ammonia. [6]

To reduce ammonia, stall bedding needs to be cleaned daily, and stalls should be stripped to the surface level on a regular basis as well. Using ammonia-reducing products can also be helpful in decreasing exposure to this noxious gas.

Different types of stall bedding vary in their ability to absorb moisture and ammonia from urine. [2] One study examining wheat straw, wood shavings, hemp, straw pellets, and paper cuttings showed the straw pellets bind ammonia and reduce its transformation to gas best. [11]

Barn Clutter

Horse owners may not think of clutter around the barn as a possible source of dust. However, old tack, blankets, tools, and equipment tend to collect dust which can make its way into the air.

Remember that every bit of dust reduction is beneficial to air quality in barns, especially when protecting equine respiratory health. [6]

Barn Management Routines

Keeping a clean barn is important to many horse owners, but the tasks of sweeping aisles and cleaning stall bedding can generate a substantial amount of dust. In fact, stall cleaning has been shown to magnify dust by nearly 16 times normal levels.

It’s important to turn horses out during these tasks. Barn workers should also wear a mask for their own protection. It will take 30 minutes to one hour for the dust to settle once cleaning tasks have been completed, so horses should not be returned to stalls until then. [6]


Once dust is in the air, the particles will stay in the atmosphere for a long time unless removed by ventilation – the process of replacing stale air with fresh air. [7]

Barns that are completely closed have little ventilation and can negatively impact a horse’s respiratory health. Ventilation can also be affected by the barn style and roof height. [7]

Another problem barns face without proper ventilation is moisture exhaled by horses with each breath. This warm, moist air rises until it meets the cold barn roof, condensing on the cold surface. Water droplets will then fall back into the stalls, possibly making your horse colder in winter.

If hay is stored in a loft, the top bales can collect moisture and mould, further adding to irritants that horses will inhale. [12]

Improving Barn Ventilation

If you are building a new barn or renovating a current barn, good ventilation should be a top priority. Adding the proper number of vents, windows, and doors will go a long way in aiding air turnover. Fresh air drafts can help minimize a horse’s exposure to harmful airborne irritants.


In the warmer months, doors and windows are often left open, resulting in better ventilation. However, barns are often closed during the colder months to prevent heat loss, and ventilation is significantly decreased or non-existent.

Though some people might think horses are more comfortable in an airtight barn, they can actually stay comfortable in unheated barns where the air is constantly exchanged, so long as barn walls block strong winds.

If horses have access to forage for most of the day and night, most horses can produce plenty of body heat through the fermentation of fibre in the gut. [12]

Air Exchange

The air exchange rate, measuring how quickly outside air replaces indoor air, is also an important consideration in barns. As fresh air from outside comes in, particle concentrations in the air are reduced, providing a healthier environment. [6]

Infiltration is unintended ventilation that occurs when air comes in through cracks in walls and floors, under doors, or through any other gaps in the barn. Although this isn’t necessarily intended ventilation, it can help to reduce dust. [6]

One way to add barn ventilation in closed barns is using inlets (vents) and outlets (cupolas).

Soffet vents can be placed under the eave of the roof and help pull cool air in while allowing warm air to escape through openings in the roof. Ridge vents can be installed along the length of the peak (or ridge) of the roof to allow warm air to escape as well. [1][6][13]

Mechanical Ventilation

Mechanical ventilation is another option. This type of ventilation uses equipment such as fans, vents in the walls, and ducts. Using strategically placed fans in conjunction with open doors and/or windows can help recirculate air and prevent it from settling inside the barn.

Proper placement of the fans is important so that dust is not blown back into horses’ breathable air space. [6]

One study showed that a balanced mechanical ventilation system with supply and exhaust air resulted in reduced levels of carbon dioxide, ammonia, ultrafine dust particles, and allergens. Overall, all horses used in this study had less airway inflammation. [13]


Respiratory disease in horses is all too common and is often affected by air quality and ventilation in barns. Turning horses out on pasture as much as possible benefits respiratory health and overall well-being, but this isn’t possible in all housing and boarding situations.

Therefore, the quality of air in the barn should be a top priority to protect horses’ respiratory health and the health of people working or spending time in the barn.

Airborne dust in barns is made up of different-sized particles of plant fragments, mites, bacteria and mould spores, yeasts, and endotoxins, all influenced by choice of stall bedding, forage, and activities such as mucking and sweeping.

Fortunately, many things can be done to improve barn air quality, including changing bedding material, soaking or steaming hay, changing barn management routines, and making structural or mechanical changes to improve ventilation.

By keeping the above information in mind, you can help protect your horse’s respiratory health and even reverse symptoms of equine asthma.

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  1. Air Quality In The Horse Barn. Horse Journals. 2023.
  2. Mönki, J. et al. Effects of Bedding Material on Equine Lower Airway Inflammation: A Crossover Study Comparing Peat and Wood Shavings. Front Vet Sci. 2021.
  3. Sheats, M.K. et al. Comparative Review of Asthma in Farmers and Horses. Curr Allergy Asthma Rep. 2022. View Summary
  4. Every cough a warning signal. Boehringer Ingelheim.
  5. Skelly, C. Health Considerations When Housing Horses. Michigan State University. 2012.
  6. Dust Management in Horse Facilities. Purdue University Extension.
  7. Auger, E.J. and Moore-Colyer, M.J.S. The Effect of Management Regime on Airborne Respirable Dust Concentrations in Two Different Types of Horse Stable Design. Journal of Equine Vet Sci. 2017.
  8. Reducing the Risk of Respiratory Ailments. University of Guelph Press Release. 2023.
  9. Kwiatkowska-Stenzel, A. et al. The effect of stable bedding materials on dust levels, microbial air contamination and equine respiratory health. Res Vet Sci. 2017. View Summary
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  11. Fleming, K. et al. Evaluation of Factors Influencing the Generation of Ammonia in Different Bedding Materials Used for Horse Keeping. Journal of Equine Vet Sci. 2008.
  12. Winter Horse Barns Need Good Ventilation. Kentucky Equine Research. 2018.
  13. Wålinder, R. et al. Installation of mechanical ventilation in a horse stable: effects on air quality and human and equine airways. Environ Health Prevent Med. 2011. View Summary
  14. Feige, K. et al. [Effects of housing, feeding and use on equine health with emphasis on respiratory and gastrointestinal diseases]. Schweiz Arch Tierheilkd. 2002. View Summary