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

In horses, we know that PM2.5 causes mEA. As such, it’s logical that smog and forest fire smoke exposure should cause exacerbation of equine asthma, but we don’t know about heart disease or risk of premature death.

Symptoms, Diagnostic Tests, and Treatments

Equine asthma manifests with a spectrum of symptoms that vary in severity and degree of debilitation they cause. Just like in people with asthma, the airways of horses with mEA and sEA are hyperreactive. This means that the asthmatic horse’s airways are extra sensitive to barn dusts that another horse’s lungs would just ignore. The asthmatic horse’s airways constrict (become narrower) in response to these dusts. This narrowing means it’s harder to get air in and out of the lungs. Think about drinking through a straw. You can drink faster with a wider straw than with a skinnier one. It’s the same with air and the airways. In horses with mEA the narrowing is mild. In horses with sEA the constriction is extreme and is the reason they develop a “heave line” — a visible line of abdominal muscles that develop as the horse tries to breathe and push air out of their narrow airways. They also develop flaring of their nostrils at rest to make their upper airway wider to get more air in. Horses with mEA do not develop a heave line, but the airway narrowing and inflammation do cause reduced athletic ability.

Another very obvious feature of horses with sEA is their persistent hacking cough, which worsens in dusty conditions such as when fed dusty hay or working in a dusty arena or on a dusty track. The cough develops because of airway hyperreactivity and because of inflammation and excess mucus in the airways. Mucus is the normal response of the lung to the presence of inhaled tiny particles or other irritants. Mucus traps these noxious substances so they can be coughed out, which protects the lung. But if an asthma-prone horse is constantly exposed to a dusty environment it leads to chronic inflammation and mucus accumulation, and the development or worsening of asthma — along with that characteristic cough.

How Veterinarians Accurately Diagnose Equine Asthma

Veterinarians use a combination of the information you tell them, their observation of the horse and the barn, and a careful physical and respiratory examination that often involves “rebreathing.” This is a technique where a bag is briefly placed over the horse’s nose causing them to breathe more frequently and more deeply to make their lung sounds louder. This helps your veterinarian hear subtle changes in air movement through the lungs and amplifies the wheezes and crackles that characterize a horse experiencing a severe asthma attack. Wheezes indicate air “whistling” through constricted airways, and crackles mean airway fluid buildup. The fluid accumulation is caused by airway inflammation and contributes to the challenge of getting air into the lung.