Windy’s Cough: Causes and Characteristics
For the past 4 years, Windy, a 12-year old Hanoverian mare, has 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 as a third-level dressage horse. Windy’s 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.
Windy came to the Hospital for Large Animals at Tufts University’s Cummings School of Veterinary Medicine for a more in-depth evaluation. On physical examination, Windy’s 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.
We examined Windy further at the Tufts Lung Function Laboratory, the only one of its kind in the Northeast. Here, we were able to test the ability of Windy’s lungs to move air effectively through her airways (see lung function testing, in our “Innovation” section), 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 Windy’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 Windy narrowed her airways 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.
To further characterize the degree and type of inflammation in Windy’s airways, we performed a bronchoalveolar lavage, or 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 Windy’s cough. Microscopic examination of the lung secretions showed a large amount of mucus and inflammatory cells, called neutrophils. Windy 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 Windy’s physical examination, history, lung function testing and BAL, she was diagnosed with inflammatory airway disease, or IAD. IAD affects a large number of stabled horses, and is due to exposure to stable dusts. People who work in poultry, cattle, hog and horse barns are also prone to the human version of IAD, called occupational asthma.
Windy 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 here at Tufts, and greatly enhances our ability to give inhaled medications to horses. We also emphasized the importance of reducing dust in the environment and feed.
Windy was scheduled for a recheck lung function test after six weeks of treatment. At this time, Windy’s 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.