Clinical and diagnostic features of inflammatory airway disease subtypes in horses examined because of poor performance: 98 cases (2004-2010).

Objective: To determine whether there are important differences relating to seasonality of signs or clinical features between subtypes of inflammatory airway disease (IAD) in horses caused by neutrophilic and eosinophilic-mastocytic inflammation having dissimilar etiopathologic pathways.

Design: Retrospective case series.

Animals: 98 horses.

Procedures: Data were compiled from medical records of horses examined because of poor performance from 2004 through 2010. Horses underwent a standardized high-speed treadmill test, lameness evaluation, cardiac evaluation, and postexercise bronchoalveolar lavage (BAL). By means of standard BAL cytologic criteria, horses were divided into 4 groups: eosinophilic-mastocytic inflammation, neutrophilia only, mixed inflammation, or no inflammation (control). Associations between IAD subtype and clinical parameters were investigated.

Results: Data for 98 horses were obtained, including age, career, season of admission, and results of hematologic evaluation, high-speed treadmill arterial blood gas analysis, upper airway endoscopy, cardiologic evaluation, and BAL. Cytologic evidence of IAD was found in 81% (79/98) of the horses, and 30% (30/98) had erythrocytes present in the BAL fluid after exercise. Horses in the eosinophilic-mastocytic inflammation and mixed-inflammation groups were significantly more likely to be Thoroughbred than Standardbred and have larger amounts of mucus in their BAL fluid. No significant differences were found in season of evaluation, results of exercising blood gas analyses, or comorbidities.

Conclusions And Clinical Relevance: No association between season and cytologic profile of BAL fluid and no major effects of IAD subtype on pulmonary gas exchange during exercise were seen in this population of horses.