Discussion

The prevalence of exercise-induced pulmonary haemorrhage (EIPH) or bleeding in the racing Thoroughbred throughout the world is extremely high, with estimates of its occurrence being dependent on various factors, including the diagnostic method employed. When endoscopic observation of blood within the trachea is set as the diagnostic criteria, most studies, involving post race tracheobronchoscopy, have found an incidence of over 50%.

It is not an infrequent request, whilst attending as a racecourse veterinary surgeon, for an endoscopic examination of the airways to be performed on a horse who has disappointed connections with its performance. Based on the reported prevalence of EIPH post racing, it is likely that one will be presented with a horse with blood in its trachea and an opinion will be required on the significance of this finding. This creates a conundrum for the veterinary surgeon, as whilst it is a widely held belief that bleeding adversely affects performance, evidence- based studies to support an opinion with regard to the effect of EIPH on performance are limited. Some studies have shown a negative effect, others revealed no association with poor performance and it has even been reported in association with better performance. The most robust study, which looked at a large number of horses (744 horses racing on the flat in Melbourne, Australia) was that of Hinchcliff et al. (2005). In this study horses tracheas were examined for blood within 2 h of racing, with the severity of EIPH being graded on a scale of 0 - 4. Parameters of performance measured were race placement, money earned and distance behind the winner. Results revealed that horses with EIPH of grade 1 were more likely to win or finish in the first 3 places and were likely to have higher race earnings. The odds of winning or finishing in the first 3 placings were no different whether grade 1 EIPH or no blood was present in the trachea. They also found an association between severity of EIPH and the severity of the impaired performance. Extrapolating from these results moderate EIPH should be considered significant with respect to performance.

There appear to be no published studies on the association of EIPH and performance in the National Hunt racehorse and it may be that Hinchcliff et al.s findings in flat racing is not applicable to this population of horses. As horses involved in National Hunt racing usually run over longer distances than those on the flat and accumulate a greater number of years racing, it is to be expected that the prevalence of bleeding will be higher. This appears to be borne out by the study of Newton et al. (2005) into epistaxis on British racecourses, which found a significantly increased risk for hurdle and steeplechase races compared to both flat and National Hunt flat races. This study also found that horses with epistaxis were significantly more likely to have a poorer finishing position than those horses without blood at their nostrils. The findings are probably not surprising as epistaxis is associated with severe EIPH. Unfortunately, studies relating epistaxis with racing performance provide only limited information regarding the association of EIPH and performance.
When asked to perform endoscopy of the respiratory tract post racing consideration should be given to a number of factors prior to carrying out the procedure. These include time elapsed from end of race, finishing position, jockeys comments, previous performance and respiratory health and any other relevant history. If blood is found in the airways it is important that the entire length of the trachea is visualised and the severity is graded. Even after taking into account findings, history and the available scientific evidence, determining the significance of the presence of blood in a horses trachea after racing remains challenging and the opinion formed must be, to a degree, subjective.