Managing Inflammatory Airway Disease in Horses (AAEP 2011)

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Originally published on TheHorse.com

Of the many ailments that can limit an athletic horse’s performance, lower airway inflammation is a top cause, affecting as many as 50% of young equine athletes. The good news about inflammatory airway disease (IAD) is the condition is treatable, and most affected horses can make a full recovery. During a presentation at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas, Harold McKenzie III, DVM, MS, Dipl. ACVIM, an assistant professor at the Marion DuPont Scott Equine Medical Center in Leesburg, Va., described in-depth how to manage IAD in performance horses.

Inflammatory airway disease most commonly affects young to middle-aged horses, although the exact prevalence remains unclear, McKenzie explained. Horses with the disease display a number of clinical signs, including:

• Mild exercise intolerance;
• Intermittent cough;
• Nasal discharge;
• Abnormalities on lung auscultation (listening with a stethoscope); and
• Tracheobronchial mucus accumulation.

McKenzie relayed that IAD has many and varied causes, and there are likely allergic, environmental, bacterial, and viral components to disease development: "Young performance horses are exposed to lots and lots of things that can initiate and prolong irritation in the respiratory tract."

He described risk factors for developing the disease:

Age: McKenzie said studies have shown that 2-year-olds in training were seven times more likely to develop IAD than 3-year-olds in training. He noted this could be because younger horses are  naive to environmental irritants or they could be less immunocompetent (i.e., have a weaker immune system) than their older counterparts. Regardless, McKenzie noted that the incidence of IAD decreases with time in training.

Intense Exercise: The deep breathing that accompanies intense exercise allows cold, dry air to enter directly into the lower respiratory tract, McKenzie explained, adding that air is warmed and humidified before it enters the lungs. The cold air and inhaled particles can induce inflammation and cause injury to the respiratory tract’s epithelial lining, leading to IAD.

Transport: McKenzie explained that transportation can mean prolonged periods of head elevation and deep inhalation of dust particles, along with stress that suppresses pulmonary macrophage function, all of which lead to lower airway inflammation and potentially IAD.

Stabling: Finally, McKenzie explained that horse’s living environment is a major contributing factor in IAD development. He noted that horses are at increased risk of developing IAD in poorly ventilated stables and when bedded on straw, as both promote airborne dust and other particles that contribute to disease.

Diagnosis and Assessment

McKenzie described some methods by which veterinarians diagnose and assess the severity of IAD, including:

• Endoscopy: The presence of pus upon endoscopic exam is indicative of IAD, McKenzie said.
• Bronchoalveolar lavage (BAL): This technique--in which the veterinarian places a small amount of sterile fluid into the lung and then draws it out for analysis, essentially "washing" part of the lung--is considered the gold standard for assessing IAD, he said. While BAL is safe and well-tolerated by most horses, he said it "doesn't look pretty" when the veterinarian performs the procedure, which can lead to some reluctance on the part of owners and trainers to have the procedure done. Veterinarians can evaluate the degree of inflammation in the small airway by examining the cells found on BAL.
• Lung function testing: While lung function testing isn't widely available due to the specialized equipment it requires, McKenzie noted it could allow for earlier detection of lower respiratory dysfunction.

Treatment and Management

Finally, McKenzie delved into the different treatment modalities veterinarians use and management options owners can employ to combat IAD.

"Treatment can be challenging at times," he admitted, adding that therapy typically consists of medical management, rest (at least two to four weeks), and husbandry changes.

Medical intervention can be effective in controlling existing inflammation, he said, however some treatment modalities can be counterproductive, masking clinical signs without improving the horse's health.

The veterinarian can use corticosteroids—either inhaled or systemic, depending on the severity of the disease—however, McKenzie noted inhaled medications are very expensive and can become cost-prohibitive with long-term use.

"Bronchodilator therapy (such as clenbuterol) can be useful in treating the patient with IAD but should not represent the cornerstone of long-term treatment because these drugs lessen the severity of airway hyper-reactivity but do not completely control the underlying inflammatory process," he said.

"Because IAD is associated with exposure to inhaled irritants … it is fundamentally a disease associated with management, and no pharmaceutical therapy will be entirely effective in the absence of dietary and environmental modifications," McKenzie stressed.

He listed the following suggestions for managing IAD-affected horses:

• Use low-dust bedding. Avoid straw and sawdust, which can promote a dusty environment. Instead, try lower-dust wood shavings.
• Enhance ventilation. Barns or stalls with poor ventilation promote IAD, so ensure horses with IAD are housed in well-ventilated environments.
• Plan chores around turnout schedules, making sure horses are outside while you’re working in the barn; excess dust and particles fill the air during stall cleaning and aisle sweeping.
• Avoid feeding dusty hay. Instead, try feeding chopped forages or a pelleted complete feed. If hay is a necessity, soak or steam it to reduce the amount of dust it contains.
• Embrace turnout. Horses with IAD benefit from being outside away from dusty environments for as much of the day as possible.

Take-Home Message

"The long-term prognosis of horses affected by IAD is not well-described, but there is some cause for concern that IAD could represent a precursor to recurrent airway obstruction if not effectively controlled," McKenzie said. "With optimal treatment, many horses can improve athletic function, although perhaps with some partial impairment in the form of exercise intolerance."

As with managing most ailments, it’s crucial to consult your veterinarian and commit to specific management changes.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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