Recurrent airway obstruction

Recurrent airway obstruction, also known as broken wind, heaves, wind-broke horse, or sometimes by the term usually reserved for humans, chronic obstructive pulmonary disease or disorder (COPD) – it is a respiratory disease or chronic condition of horses involving an allergic bronchitis characterised by wheezing, coughing and laboured breathing. Symptoms include, primarily, increased respiratory effort and dyspnea, especially in response to strenuous exercise. In some cases (secondarily), the horse may present with acute severe dyspnea, such that it really struggles to inspire sufficient air. This is a veterinary emergency. In addition, a soft, moist cough may be seen, most commonly in association with exercise or eating. This cough may be productive, with expectoration of thick, viscous sputum. There may also be an audible wheeze. In chronic cases, a "heave line" may be visible on the ventral abdomen. This is caused by hypertrophy of the extrinsic respiratory muscles. If any of these symptoms are observed, veterinary advice should be sought. The veterinarian will usually auscultate (listen to the horse's chest with a stethoscope) to attempt to detect adventitious lung sounds. If these are very quiet, a rebreathing bag may be used - a plastic bag over the nose to intensify the horse's respiratory effort and hence the sounds. This procedure can be dangerous and should not be attempted by non-professionals. Blood gas analysis may also be carried out, although it is rarely required. In some cases, a bronchoalveolar lavage may be carried out - an endoscope is used to look down the trachea, and mucus and cells are washed out of the lower airways for analysis. Typically, a BAL recovers an abnormally high percentage of neutrophils from an RAO horse - up to 50 or 70% in severe cases. An allergic reaction to certain otherwise innocuous substances - allergens, typically dust and mold spores (e.g. Aspergillus spp.). It is therefore most common in horses fed on hay and bedded on straw. Endotoxins from organisms in the bedding and feedstuffs may also play a role.