Preventing and Treating Lower Respiratory Tract Disease in Horses

Considerable demands are placed on the equine athlete’s lungs during strenuous exercise. To support respiratory tract health in horses, special attention must be paid to the quality of the air they breathe, even when they are at rest. Basic stable management to maximize air quality and support respiratory health includes the following steps:

Dampen or soak hay that is fed indoors.

• Sprinkle the barn aisle with water when sweeping.
• Remove horses from barn during cleaning.
• Turn out horses as much as possible.
• Use a low-dust bedding with a daily mucking out.
• Consider ventilation during all seasons.
• Keep vaccinations up to date.
• Exercise horses regularly.

Noninfectious respiratory diseases in horses include lower respiratory tract inflammation (LRTI) and heaves. Management practices to prevent and treat these problems have some similarities as well as some important differences.

The treatment of heaves can be seen as a series of steps beginning with the easiest and least invasive. If symptoms persist or worsen, steps can be added until satisfactory control occurs. Once the horse is stabilized, the pyramid can be descended as tiers are progressively removed.

Environmental management is the first and most important component of treating and preventing heaves. Failure to properly attend to air hygiene is the primary reason for failure of therapeutic regimens. Poor air quality is also an important causative factor associated with LRTI. Inhaled mold spores can induce a primary inflammatory response without an allergic reaction occurring. However, it must also be remembered that infectious agents including viruses, bacteria, and mycoplasms are involved in many episodes of LRTI.

Even when these pathogens are involved, attention to air hygiene is important in decreasing the severity of symptoms in individual cases and also in hastening recovery from an infection. Critical factors in environmental management in relation to air hygiene of stables include providing adequate ventilation and drainage; using bedding materials that are as free as possible of dust and mold; and considering forage products other than traditionally made hay.

Bronchodilators and mucolytics form the next step. Increased production and accumulation of thick tenacious mucus are common pathophysiological changes associated with diseases of the lower airways. The beta-2 agonist clenbuterol (Ventipulmin) is the most widely used bronchodilator in equine practice. Anticholinergics such as atropine are effective as bronchodilators but can have unwanted systemic side effects. Xanthene derivatives including theophylline and aminophylline are bronchodilators, but have short durations of action and side effects including tachycardia and sweating which are frequently seen due to their narrow therapeutic margin. The mucolytic agent dembrexine is often used in combination with a beta-2 agonist to alleviate symptoms associated with accumulation of mucus. Mucolytic agents help to decrease the viscosity of thick tenacious mucus while the beta-2 agonist will stimulate mucociliary clearance enhancing the removal of mucus from the lungs.

The administration of sodium cromoglycate by nebulizer once a day for five days can provide up to a month of prophylaxis to asymptomatic heavey horses exposed to poor air hygiene. There does appear to be individual variation in responsiveness to sodium cromoglycate. Sodium cromoglycate is known as a mast cell stabilizer. There may be another mechanism by which it induces protection to inhaled allergens.

Nebulization of clenbuterol has been shown to be effective in inducing bronchodilation in horses that do not respond to intravenous or oral clenbuterol. Ipratropium bromide is an atropinic agent that induces bronchodilation when administered by nebulization. One advantage of nebulization is that it can be used to avoid unwanted side effects associated with systemic administration of pharmaceuticals; however, there is added inconvenience and cost associated with the use of nebulization. While there are unlikely to be a lot of new drugs to treat respiratory disease in the future, new technologies such as inhalers may facilitate the delivery of pharmaceuticals directly into the lungs.

Oral corticosteroids are used to treat heaves, though laminitis is a steroid-induced side effect that is cause for concern. Care should also be taken in administering corticosteroids to horses that may have a respiratory tract infection. These risks can be minimized by careful choice of dose and frequency of administration. Dosage should be decreased as the horse’s condition improves. Another strategy involves the simultaneous use of a corticosteroid with a beta-2 agonist.

Pharmaceuticals will continue to have an important role in treating respiratory problems of horses. Prevention of respiratory disease is better than cure, and the earlier treatment is commenced, the sooner the horse will recover.