Airway inflammation in horses is a relatively common condition and is very similar to asthma in humans. Clinical signs include coughing, increased respiratory effort, mucoid nasal discharge, development of a heave line, and exercise intolerance. Over the years, such inflammatory conditions have had several names. Acute and milder conditions have been referred to as inflammatory airway disease, whereas chronic or longstanding, more severe conditions have been known as heaves, chronic obstructive pulmonary disease (COPD), RAO (recurrent airway obstruction), and allergic airway disease. Chronic airway inflammation is now more recently known as equine asthma.
Although there may be some genetic predisposition in some horses, it is thought that equine asthma is primarily due to hypersensitization of the lungs to allergens such as pollens, mold spores, dust, and endotoxins found in straw and hay. Recurrent airway conditions in some horses are due to stabling, poor air circulation, and excessive exposure to the aforementioned allergens. Asthma can also be seen in horses that live primarily outside, and in these cases the cause is thought to be exposure to pollens, weeds, dust and chemicals aerosolized during agricultural work.
Inflammatory airway disease tends to be less severe and seems to happen more commonly among younger horses. It often follows infection with a respiratory virus, and is characterized by intermittent coughing and exercise intolerance; however, these horses are usually normal at rest. More chronic and recurrent conditions (RAO, COPD, asthma) often manifest themselves by way of exercise intolerance, mucoid nasal discharge, increased respiratory effort even at rest, frequent coughing, sometimes with resultant mucus plugs being expelled. Horses that are poorly controlled and affected long-term often experience weight loss and hypertrophy of abdominal muscles (heave line).
There Is No Cure For Asthma
Equine asthma is similar to human asthma in that inflammation due to allergens will result in airway constriction, mucus build-up, and spasm of the bronchi. There is no cure for asthma. The goal is to treat clinical signs as effectively as possible with medication during flare ups, and then managing the condition by controlling environmental factors to prevent flare ups. Environmental management is the most important aspect of asthma treatment. Elimination or reduction of exposure to allergens and triggers is incredibly important. This can be accomplished by avoiding hay storage in the barn or in hay lofts above the horse where dust falls through the hay loft floor, avoiding sweeping and grooming around the affected horse, feeding moistened or soaked feed materials to remove or reduce dust, pollens, and mold spores, and providing ample ventilation to the affected horse. Dusty riding arenas are not ideal, and for those horses that tend to be reactive outside in the summertime, stabling during those time periods may be required to keep airway flare ups to a minimum.
Photo of an Equine Asthma Hay Condom
Photo of an Equine Plastic Hay Feeder
Medical treatment usually consists of steroid anti-inflammatories, bronchodilators, and sometimes expectorants. Short term treatment with oral or injectable steroids is usually not a concern with regard to side effects, but for horses requiring long-term treatment or repeated treatment throughout the year, it would be much safer and sometimes ultimately more effective to use inhaled medications. These are administered using special aerosol chambers such as the Aerohippus, or via a nebulizer. Medications administered in this fashion tend to be delivered mostly to the lungs for which they are intended, and there appears to be very little systemic absorption, making them much safer with regard to side effects.
It is important to implement a treatment plan for a horse with lung inflammation as soon as possible, as these asthma type conditions can cause permanent damage to the lung tissue and can render the lungs unresponsive to medications with time. This disease can be severely debilitating and can decrease an animal's quality of life such that sometimes euthanasia is the kindest treatment option.
Horses tend to be eager to please their humans, and sometimes the degree of struggle they experience goes unnoticed because the horse is still eating and seeming perky otherwise.