Respiratory diseases in horses can be grouped into two general categories – infectious and noninfectious. Infectious respiratory diseases include bacterial and viral infections. The most common of the non-infectious respiratory conditions are Small Airway Inflammatory Disease (SAID) and its more severe form known as “heaves” or Recurrent Airway Obstruction (RAO).
As its name implies SAID is an inflammatory condition of the very small airways deep within the horse’s lungs, similar to asthma in humans. RAO or “heaves” is a chronic, recurrent condition characterized by obstruction of the airways with mucus and constriction of the airways that result in more severe clinical signs, similar to emphysema in humans.
Keep in mind that horses have tremendous lung capacity. For example, a racehorse running at top speed breathes about 120 times per minute, moving about 12-15 liters of air per breath or 1,400-1,800 liters per minute through the lungs. A horse at rest uses only a mere fraction of his/her full lung capacity. Therefore, the degree of clinical signs you may observe will vary depending on the horse’s endeavors.
SAID is diagnosed based on history, clinical signs, physical exam findings, and diagnostic tests including:
RAO is most often diagnosed simply based on history, clinical signs and physical exam findings. It is often not necessary to perform the other tests described above due to the more severe nature of the disease, though testing can help identify the most appropriate treatment
Medical treatments, as well as environmental management strategies, are employed. Medical treatment includes drugs to control airway inflammation and bronchoconstriction. Oral corticosteroids such as prednisolone (not to be confused with the steroids used by some athletes) are effective at reducing airway inflammation. Inhaled steroids are very effective and allow delivery of the drug directly to the lungs while decreasing the potential adverse side effects (immunosuppression, laminitis, adrenal gland suppression). Bronchodilators provide relief of airway constriction making it easier to breathe and decreasing coughing.
Oral anti-histamines do not work well in horses with these conditions.
Once the clinical signs have been controlled medically, environmental management becomes the MOST IMPORTANT part of long term treatment. Our recommendations include:
SAID can be treated effectively in most cases. As stated above however, certain horses are more prone to having hyper-reactive airways which predispose them to repeated episodes. This is why environmental management is so important. In many patients there is a seasonal component with episodes being worse in spring and fall due to environmental allergens. Some horses are worse in the winter when they spend more time inside the barn. SAID that is not effectively managed can develop into RAO. RAO that is not effectively controlled can ultimately result in irreversible scarring and fibrosis of the lungs.