Equine recurrent airway obstruction and summer pasture-associated obstructive pulmonary disease are the major causes of chronic poor performance and exercise intolerance in athletic horses. Conventional treatment includes administration of a bronchodilator, an anti-inflammatory agent, and elimination of the inciting environment. Affected horses usually require life-long medication. If a corticosteroid is being used as the anti-inflammatory agent, an iatrogenic immune suppression and repression of the endogenous adrenocorticosteroid production are the most common side effects. Chinese veterinary herbal medicine provides an alternative long-term therapy with minimal side effects. Four common Chinese herbal formulas, Schisandra 5, Lily Combination, Bu Fei San, and Breath Easer have been shown to be useful for treating chronic
respiratory disease. The pharmacological mechanisms of the phytochemical compounds present in 23 herbs found in these formulas are reviewed in this article. Active phytochemical compounds in the herbs are found in the form of primary and secondary metabolites. They may possess antimicrobial, antioxidant, anti-inflammatory, antihistamine, or antitussive properties alone or in combination. The evidence for a relevant pharmacological mechanism of the active phytochemical compounds in each herb validates the use of Chinese herbal supplements for treating chronic respiratory problems. These findings emphasize that the development of herbal formulas by ancient Chinese herbalists was conducted cautiously and based on a unique knowledge of pharmacology and toxicology.