For 4 years, a 12-year-old Hanoverian mare had a mild cough whenever her barn was closed up against the cold in the winter. Last year, the cough did not go away – and even seemed to be worse during the hot, humid weather in the late spring and summer. The cough was now interfering with the horse’s work at third-level dressage. Her primary care veterinarian had recommended treatment with dexamethasone, a corticosteroid. The medication seemed to help, but the cough came back as soon as the treatment was discontinued.
The mare came to the Hospital for Large Animals at Cummings Veterinary Medical Center for a more in-depth evaluation. Upon physical examination, her breathing rate was slightly higher than usual (about 20 breaths per minute). There was also a small trickle of white discharge from both nostrils. When we listened to the air moving through her trachea, or windpipe, we could hear a rattling noise–which suggested the presence of mucus in her airways.
In our Lung Function Laboratory, we were able to test the ability of the mare's lungs to move air effectively through her airways and found that her baseline resistance was only slightly elevated, an indicator of mild airway narrowing. This was good news, as it suggested a lower level of lung dysfunction. To determine if the patient's lungs were “twitchy,” or more responsive to stimuli as often seen in horses with inflammatory airway disease, we performed a histamine bronchoprovocation test. These results showed that her airways narrowed when exposed to very low levels of histamine, a substance that may be released in the horse’s lung when it is irritated by a dusty environment or cold temperatures.
This image shows the cytology of a bronchoalveolar lavage (BAL or lung wash) from a horse with inflammatory airway disease (IAD). This horse has many mast cells, as well as neutrophils and particulates from exposure to barn dust.
To further characterize the degree and type of inflammation in the mare's airways, we performed a bronchoalveolar lavage (BAL), using a thin, 2.3-meter videoscope. After examining the larger airways, we infused sterile saline into the lower lung and quickly suctioned it back. This gave us a sample of the abnormal inflammatory cells and mucus that were causing her cough. Microscopic examination of the lung secretions showed a large amount of mucus and inflammatory cells, called neutrophils. The patient also had an elevated number of mast cells, another type of inflammatory cell that contributes to airway reactivity, or twitchiness (see image).
Based on the results of the mare’s physical examination, history, lung function testing, and BAL, she was diagnosed with inflammatory airway disease, (IAD). IAD affects a large number of stabled horses and is due to exposure to stable dust. People who work in poultry, cattle, hog, and horse barns are also prone to the human version of IAD, called occupational asthma.
The patient was treated with a four-week, tapering course of corticosteroids as well as inhaled medications: both a corticosteroid and a bronchodilator called albuterol. The inhalers were administered using the AeroHippusTM, a delivery device that was developed at Cummings Veterinary Medical Center, and greatly enhances our ability to give inhaled medications to horses. We also emphasized the importance of reducing dust in the environment and feed.
The patient had a recheck lung function test after six weeks of treatment, at which time, her airways were decidedly less twitchy, she was no longer coughing, and her performance was back on par. We emphasized to her owner that IAD is a disease that is rarely cured but can be well-managed to keep a horse a functional athlete.