Inflammatory Airway Disease

A recent Australian study investigated inflammatory airway disease (IAD) in two and three year old racing Thoroughbreds, to determine the incidence of IAD in young Thoroughbred racehorses entering racetrack stables for training; investigate non-infectious stable management and environmental risk factors of IAD, and to determine the concentrations of specific dust toxins in stable environments and their association with IAD. (N Malikides and J.L. Hodgson, Inflammatory Airway Disease in Young Thoroughbred Racehorses, RIRDC Project US 82-A, October 2003).

During the study it was found that more than a third of horses entering stables for training already had some form of lower airway inflammation.

In the horses who were IAD free upon arrival, approximately 40% developed neutrophilic lower airway inflammation within the first 2 weeks of stabling. In almost half of these racehorses lower airway inflammation persists and with increased training and management stresses, this inflammation may develop into clinical disease.

Significant risk factors identified for the development of neutrophilic IAD in young thoroughbred racehorses included:

  • The severity of airway inflammation is related to the endotoxin concentration of inhaled dust.
  • Ventilation quality and meteorological conditions, particularly evaporation level in loose boxes and stables (i.e. number of open windows in the loose box and carbon dioxide concentration in boxes).
  • The health management and conditions to which young racehorses are subjected prior to transport to stables may be influential in whether or not horses arrive with some form of IAD.
  • Horses who are fed ‘high dust’ hay (i.e. straw-like versus lucerne or clover hay) are more susceptible, as these feeds contain higher concentrations of ‘dust constituents’.
  • Exposure to only 2 weeks of poor natural ventilation is likely to result in the development of lower airway inflammation. This may be due to the effects of increased concentrations of airborne dust and noxious gases such as ammonia.

Stable design and management practices recommended to reduce the incidence of IAD:

  • Loose boxes with at least one open window or all four walls open to constant ventilation.
  • Decreasing exposure to dust by reducing the overall airborne dust concentrations, i.e. using a broom and water to clean down stable pathways, wetting down bedding and feed, use of fans to circulate air and draw dust particles out of the stables.
  • Repetitive endoscopic examinations may be useful to gauge the progression and nature of tracheal discharge.

The full report on Inflammatory Airway Disease in Young Thoroughbred Racehorses can be obtained from the RIRDC website (