It's Warm Weather but My Horse Coughs - What's the Problem?

During the warm weather of summer time, seeing or hearing a horse cough may seem unusual, but horses and people sometimes have respiratory problems that lead to coughing during any season of the year.

If your horse coughs several times at the beginning of exercise, he may have upper airway irritation, tracheal irritation, allergies or a respiratory condition called inflammatory airway disease. Inflammatory airway disease is a chronic inflammatory condition of the lower airways of younger horses characterized by chronic cough, excess mucus in the trachea, and mild exercise intolerance.

Horses with upper airway irritation usually have normal attitudes, appetites, and temperatures and do not exhibit increased respiratory effort at rest. Inflammation and mild airway obstruction with mucus occurs in the bronchi and bronchioles resulting in bronchitis. It is often caused by substances that irritate the airways such as molds, dusts, or pollutants. 

A general physical examination with attention to the respiratory system may or may not show that there is some clear or white discharge present in the nostrils.Listening to the lungs and trachea may reveal harsh sounds, crackles, wheezes, or fluidy sounds in the trachea suggestive of the presence of mucus or lung sounds may be normal.

Source: http://equimed.com