The Impact of Air Quality and Pollution on Your Horse’s Lungs

There’s nothing like hearing a horse cough to set people scurrying around the barn to identify the culprit. After all, that cough could mean choke, or suggest that a respiratory virus has found its way into the barn. It could also indicate equine asthma. Yes, even those “everyday coughs” that we sometimes dismiss as “summer cough” or “hay cough” are a wake-up call to the potential for severe equine asthma. 

Formerly known as heaves, broken wind, emphysema, chronic obstructive pulmonary disease (COPD), or recurrent airway obstruction (RAO), this respiratory condition is now called severe equine asthma (sEA). These names reflect how our scientific and medical understanding of this debilitating disease has changed over the years. We now consider heaves to be most comparable to severe asthma in people.

But what if your horse only coughs during or after exercise? This type of cough can mean that the horse has upper airway irritation (throat and windpipe) or lower airway inflammation (lungs) meaning inflammatory airway disease (IAD) — which is now known as mild-to-moderate equine asthma (mEA). This airway disease is similar to childhood asthma, including that it can go away on its own. The disease causes reduced athletic performance, and a proper diagnosis by a veterinarian is important because there are different subtypes of mEA which benefit from specific medical therapies. In some cases, mEA progresses to sEA.

The Relationship Between Equine Asthma and Air Quality

Equine asthma has a lot to do with air quality. Poor air quality, or air pollution, includes barn dusts — the allergens and molds in hay and the bacteria in tiny particles of manure — as well as arena dusts and ammonia from urine. Also, gas and diesel-powered equipment contribute to air pollution for both people and horses, resulting from equipment being driven through the barn, a truck left idling by a stall window, or the smog from even a small city drifting nearly invisibly over the surrounding farmland. Forest fire smoke is another serious contributor to air pollution. 

Smog causes the lung inflammation associated with mEA. Therefore, it is also likely that air pollution from engines and forest fires will trigger asthma attacks in horses with sEA. Smog and smoke contain many harmful particulates and gasses, but very importantly they also contain fine particulate matter known as PM2.5 (referring to the diameter of the particle being 2.5 microns). That level is roughly 30 times smaller than the diameter of a human hair. Because it is so small, this fine particulate is inhaled deeply into the lungs where it crosses over into the blood stream. So, not only does PM2.5 cause lung disease, it also causes inflammation elsewhere in the body including the heart. Worldwide, even short-term exposure is associated with an increased risk of premature death from heart disease, stroke, and lung cancer.