Evidence of an association between inflammatory airway disease and EIPH in young Thoroughbreds during training.

In an epidemiological study of risk factors for exercise-induced pulmonary haemorrhage (EIPH) in young Thoroughbreds in the UK, in which 148 horses contributed 1614 horse-months of data, there were 64 (4%) episodes of endoscopically visible tracheal bleeding and 824 (51%) episodes of increased quantities of haemosiderophages in tracheal washes. There were increases in prevalence and risk of EIPH by both definitions with age from < or = 2- > or = 4 years, season of sampling from winter (Nov-Jan) to autumn (Aug-Oct) and several different measures of airway inflammation, including tracheal mucus, neutrophil proportion, inflammation score and fungal material in tracheal washes. There was considerable variability in the prevalence of EIPH between trainers. EIPH in the preceding month significantly increased the risk of the condition the following month. There was no evidence that EIPH was associated with infection of the airways with even large numbers of Streptococcus zooepidemicus or Pasteurella-like spp., which are significantly associated with airway inflammation in younger racehorses. Multiple logistic regression modelling that took account of random variability between horses and the effects of each trainer and an episode the preceding month, confirmed that after controlling for the other risk factors, EIPH was still significantly associated with increasing age, different seasons, airway inflammation and evidence of airway fungal material.