Descriptive results from a longitudinal study of airway inflammation in British National Hunt racehorses.

This research study investigates airway inflammation in British National Hunt racehorses, examining whether the decline in inflammation rates is due to the aging of the horses or their prolonged exposure to a training environment. The study further compares inflammation rates by tracheal sampling and measures the prevalence of certain symptoms among horses with different ages and training histories.

Study Methods

• The researchers conducted a prospective, longitudinal study over a two-year period on 5 National Hunt yards, which are the places where horses are bred and trained for steeplechase racing.
• They assessed the presence of nasal discharge, tracheal mucus, airway neutrophilia (an excess of neutrophils in the blood that can indicate inflammation or infection), and ‘trIAD’, a combined measure of tracheal mucus and airway neutrophilia. These components were used to diagnose inflammatory airway disease.
• The prevalence of these symptoms was then compared between horses of different ages and those with varying lengths of time in training.

Study Results

• Horses new to training were found to have twice the odds of visible tracheal mucus as compared to those formerly trained for flat racing. However, the same group did not show a significant increase in odds of airway neutrophilia.
• The evidence surrounding increased odds of trIAD in horses new to training was inconclusive.
• A shorter duration of time in training was significantly associated with the presence of visible mucus, increased mucus and trIAD.
• No measures of the disease varied significantly with age.

Conclusions

• The researchers concluded that tracheal mucus and trIAD, but not neutrophilia detected in tracheal wash samples, were less prevalent in horses that had spent more time in a training environment, hence, the decline in inflammation rates is likely linked to time in training rather than age.
• The proportion of neutrophils in tracheal wash samples was found to be less useful as a clinical tool than measures of visible tracheal mucus for identifying horses requiring treatment or changes in management.
• They proposed re-evaluation of the inclusion or relative weighting of tracheal wash neutrophils in the assessment of equine airways in the definition of trIAD.