Prevalence of inflammatory airway disease in National Hunt horses referred for investigation of poor athletic performance

Abstract

Inflammatory airway disease (IAD) is thought to be an important cause of poor performance in young Thoroughbred racehorses. However, little study has been made of IAD in older National Hunt (NH) horses. To determine the prevalence of IAD in NH racehorses referred for investigation of poor athletic performance and identify some of the risk factors that may be associated with IAD in this group of horses. Tracheal mucus was graded, and tracheal wash (TW) and bronchoalveolar lavage (BAL) performed after treadmill exercise in 91 NH horses referred to the University of Bristol. Comparisons were made between the different methods for diagnosing IAD and potential risk factors investigated. Tracheal mucus was observed in 68% and lower airway inflammation identified in 70% of horses. There was poor agreement between TW and BAL techniques for a diagnosis of IAD. The prevalence of increased proportions of neutrophils in TW was 40% compared with 59% in BAL. There was a significant association between presence of tracheal mucus and increased neutrophils in TW but not between tracheal mucus and BAL cytology. No significant association between IAD and age, EIPH or URT obstruction was observed. Inflammatory airway disease was a common finding in NH horses referred for investigation of poor performance. In contrast to studies in younger, flat racehorses the prevalence of disease did not decrease with increasing age. Horses of all ages presented for investigation of poor performance require a thorough clinical investigation of the lower airways. The collection of both TW and BAL samples is indicated in order to confirm a diagnosis of IAD.