Discussion

Exercise-induced pulmonary haemorrhage (EIPH) is common, if not ubiquitous, in horses undertaking moderate to intense exercise. A number of endoscopic surveys of EIPH in racehorses have described the incidence (the chance that an individual horse on a single occasion will have blood in the trachea post exercise) as being between 30 and 80%. If multiple examinations are made on the same horse, the incidence rises to 82 - 100%. The incidence of epistaxsis associated with Thoroughbred and Arab racing in Japan has reported to be 0.15% (Takahashi et al. 2001). Risk factors for epistaxis included jump racing, age greater than 2 years, race distances of less than 1600 m (1 mile), females. The recurrence rate in individual horses was relatively low (4.6%). In contrast to endoscopic EIPH and performance, epistaxis was shown to have a significant effect on the performance of Thoroughbred racehorses in Korea (Byungsun et al. 1998).
Epistaxis has been shown to have a marked negative effect on performance (e.g. Newton et al. 2005). However the effects of endoscopically diagnosed EIPH on performance have been less clear with studies reporting a negative (Mason et al. 1983; Hillidge et al. 1985; Kim et al. 1988; MacNamara et al. 1990; Hinchcliff et al. 2005), no (Pascoe et al. 1981; Raphel and Soma 1982; Speirs et al. 1982; Roberts et al. 1993; Lapointe et al. 1994; Doucet and Viel 2002; Birks et al. 2002) and in some cases a positive effect on performance (Rohrbach 1990; Saulez 2007). Whilst single bouts of EIPH may not even be apparent to the rider, owner or trainer of a horse unless an endoscopic examination is undertaken, the effect on performance within a single race appears to be significant but relatively subtle (Hinchcliff et al.
2005). In this latter study, horses finishing races with grade 4 EIPH were on average 6 metres behind those finishing with grade 0. However, the effect of repeated bouts of EIPH that occur with daily training may lead to more significant changes and a greater degree of tissue damage over time (see Derksen et al. 2009) with consequent loss of lung function and decreased performance.