Eosinophilic asthma in sporthorses

In order to identify typical clinical features of eosinophilic asthma in sporthorses a retrospective study was performed in 147 Standardbreds and 123 Warmblood sporthorses diagnosed with IAD. Horses with a clear positive tracheal wash culture or with RAO were excluded. Horses were subjected to respiratory endoscopy (grading mucus and blood), tracheal wash and broncheoalveolar lavage (BAL). The prevalence of eosinophilic IAD was higher in the Standardbred population compared to Warmbloods (p=0.001 Chi-square, p=0.002 bi-log regression). An increase of eosinophils in the BALF (>1%) of Standardbreds or Warmbloods was more often associated with a normal cell count of neutrophils in the BALF (p=0.04 Chi-square and p=0.004 resp.). Eosinophilic IAD was more prevalent in Warmblood horses <5 years (p= 0.01 Chi-square) compared to >5years. In the Standardbred population there was no age difference. Increase of eosinophils was, in contrast to neutrophils, not associated with cough nor increased mucus score. This study suggests eosinophilic IAD may be exercise related comparable to nonallergic eosinophilic asthma in humans1. This is in accordance with Hare2 suggesting eosinophilic IAD in racehorses is of non-allergic origin and associated with racing and airway hyperresponsiveness. A follow-up study in which Standardbreds that do not race are compared to racing Standardbreds might clarify this hypothesis.