Risk Factors for Inflammatory Airway Disease in UK National Hunt Racehorses

Inflammatory Airway Disease (IAD), defined as a combination of increased tracheal mucus and airway neutrophilia, is the most common form of respiratory disease in young racehorses (≤ 4 years old) in the United Kingdom1-3. Many studies have identified an association between certain bacterial species, particularly S. zooepidemicus, and IAD in young racehorses1, 3-5. The prevalence and incidence of IAD have been shown to reduce between the ages of 2 and 4 years, mirrored by a reduction in the incidence and prevalence of infections with S. pneumoniae and S. zooepidemicus2, 3. It has also been shown that the longer a horse has spent in training, the less likely it is to suffer respiratory disease, even having adjusted for age6, 7. Most research to date has focused on populations of young racehorses in training for flat racing. Less is known about the epidemiology of IAD in older National Hunt (NH) racehorses. The aim of this study was to describe the epidemiology of IAD in NH racehorses. The primary hypothesis was that the age-dependent reductions in prevalence and incidence observed in young racehorses are associated with time in training rather than age per se. The basis of this hypothesis was that exposure to pathogens in the training environment and subsequent acquisition of immunity results in reduced prevalence of disease over time. […]