Obstructive pulmonary disease in 18 horses at summer pasture.

The clinical features of 18 cases of summer pasture associated obstructive pulmonary disease were reviewed. The horses had signs of obstructive pulmonary disease (expiratory dyspnoea, wheezing and crackling lung sounds and coughing) during the spring, summer or autumn while they were kept permanently at grass with no access to hay or straw, for at least two consecutive years. In nine cases there was a seasonal incidence with the disease occurring during April and May. Eleven of the horses were affected by bouts of severe dyspnoea. Eleven of the horses also suffered from chronic obstructive pulmonary disease and two were affected by idiopathic headshaking. Endoscopy revealed evidence of lower airway inflammation, and a cytological examination of tracheal aspirates and bronchoalveolar lavage fluid revealed a neutrophilia. Moving the horses into a stable controlled the clinical disease effectively in only two of the 16 cases. Oral clenbuterol was effective in only seven of 15 cases. Systemic dexamethasone or oral prednisolone, in combination with clenbuterol, was the most effective treatment.