It’s not hard to understand why heaves matters to a horse. When a heaves-affected horse can hardly walk from the barn to the paddock, it’s clear that that horse has a poor quality of life, let alone having any athletic ability. But what about the horse with IAD? If it were just a cough or an occasional drippy nose, IAD would be annoying but no more. The reason that IAD matters is that it affects athletic function. Horses with constricted airways have trouble getting enough air out of their airways, and this eventually leads to uneven ventilation of the lung. Parts of the lung get enough oxygen, and other parts don’t. Overall, this leads to hypoxemia, or low blood oxygen levels, during exercise. Low blood oxygen levels in turn lead to fatigue, which can contribute to injury in addition to poor performance. Moreover, there is emerging evidence that horses with IAD have a much higher risk of eventually developing the more severe disease, heaves. If we recognize and treat IAD at an early stage, we have a better chance of preventing severe and debilitating disease later in life.