Texas Equine Veterinary Association

www.texasequineva.com • 13 Mild-Moderate Equine Asthma (IAD) Severe Equine Asthma (RAO, SP-RAO) Age of Onset Any age >7 years of age Clinical Signs at Rest No increase in respiratory effort at rest Poor performance Occasional coughing Increase in respiratory effort at rest Frequent coughing Exercise intolerance Genetic Predisposition Undetermined Yes in some families Disease Course Lasts at least 4 weeks May improve spontaneously Low risk of recurrence Lasts weeks to months May improve with environmental control +/- treatment Incurable but can control signs Diagnosis Pulmonary function testing BAL fluid cytology BAL fluid cytology Pulmonary function testing e pathogenesis of equine asthma is multifactorial but includes specific pulmonary hypersensitivity to inhaled antigens (e.g. hay dust, mold, forage mites, spores, endotoxins, and inorganic compounds) from feed and bedding that triggers airway inflammation in susceptible horses. Classically, clinical signs are worse when horses are housed indoors for long periods, but with summer pasture associated asthma, flare-ups tend to occur in the summer months while at pasture. Subsequent to the airway inflammation, horses with severe equine asthma develop increased mucus production, bronchoconstriction, airway wall thickening, and airway remodeling. While history and clinical signs may point towards severe equine asthma, the use of bronchoalveolar cytology to confirm the diagnosis is still important. Healthy airways contain primarily macrophages and lymphocytes, with normal BALF containing <5% neutrophils, <2% mast cells, and <1% eosinophils1. Changes in these cell populations support the diagnosis of equine asthma as well as providing a measure of inflammation severity that may help in treatment selection and establishing treatment expectations. Pulmonary function testing is not widely available at this time, but can be extremely useful in the diagnosis of mild to moderate equine asthma as well as monitoring treatment response. Endoscopy, especially use of dynamic upper airway endoscopy, can be used to rule out upper airway abnormalities that may be contributing to cough or exercise intolerance. Treatment of equine asthma is three-pronged with environmental modification being the most important step. When that is not possible or is insufficient in reducing clinical signs, then pharmacological treatment with glucocorticoids and/or bronchodilators can be pursued.

• Cover