EIPH: An Australian Perspective with Worldwide Implications

Exercise-induced pulmonary haemorrhage (EIPH) is a common disease of racehorses. The precise cause of EIPH is yet to be fully determined, but a well-accepted theory is that lung blood vessels rupture in response to the extremely high blood pressure and low airway pressure experienced during strenuous exercise. The barrier that separates the airway from the blood vessels is ultra-thin to facilitate the efficient exchange of gases, but this predisposes to breakage. The condition is most frequently described in Thoroughbred and Standardbred racehorses, but it has also been identified in racing Appaloosas and Quarter Horses, as well as horses involved in other high intensity athletic activities, including showjumpers, 3-day eventers, barrel racers, steeplechasers and polo horses.  EIPH is not unique to horses and has been reported in human athletes, as well as racing greyhounds and camels. Our group at Murdoch University in Perth Australia has had an interest in EIPH, which has led to three recent publications in the  Equine Veterinary Journal .1-3    How common is EIPH?    (Fig 1 near here)  Blood from both nostrils—also known as epistaxis—is the most obvious manifestation of EIPH and occurs between 1.5 and 8.4/1000 race starts, varying with racing jurisdiction. Epistaxis represents a severe manifestation of EIPH, and basing surveys on its presence vastly underestimates the true prevalence of lung haemorrhage. There are several techniques used to diagnose EIPH, but endoscopy of the trachea 30-120 minutes after racing or galloping is a common and reliable method. Occurrence and severity of pulmonary haemorrhage is typically graded using a 0-4 scale. Using endoscopy, we reported a prevalence of EIPH post-race in Australian thoroughbreds racing on turf tracks of around 55%, with most positive horses having low to moderate volumes of blood in the trachea. EIPH is less common if horses are examined after trialling, and reduced further if examined after track gallops. The prevalence of EIPH increases when horses are examined on multiple occasions after racing, and in fact all horses in our research population that had seven monitored race-starts experienced EIPH on at least one occasion.     <Figs 2 -4 near here>>    What is the effect of EIPH on race-day performance?    It is generally considered that EIPH has a negative impact on racing performance, but evidence for this assertion is surprisingly lacking. We performed 3,794 post-race endoscopy exams on over 1,500 Australian horses and reported that inferior race-day performance was limited to horses with severe EIPH (grades 3 and 4); this reflected only 6.3% of all examinations. Horses with the highest grades of EIPH (grade 4) were less likely to finish in the first three, finished further from the winner, were less likely to collect race earnings, were slower over the final stages of the race, and were more likely to be overtaken by other competitors in the home straight than horses without EIPH. Interestingly, horses with EIPH grade 1 or 2 were more likely to overtake others in the home straight, compared to horses without EIPH (grade 0). It is highly unlikely that low-grade EIPH (grade 1 or 2) confers an athletic advantage; a plausible explanation is that horses that are ridden competitively to the finish are functioning at their maximal physiological limit, compared to horses that are eased up, and overtaken, during the finishing stages of the race because they are not in prize contention or are affected by interference in the home straight. Another interesting finding was that horses with moderate to severe EIPH (grades 3 or 4) raced the early and mid-sections of the race faster than horses without EIPH. It is possible that these horses reach the breaking threshold of the small lung blood vessels at an earlier stage in the race compared to horses that start the race slower, compounding the severity thereafter. A study of barrel racing horses reported that horses with the most severe grade of EIPH were faster than horses without EIPH, a finding which may also reflect this rapid acceleration increasing the risk of EIPH. It may be wise for trainers to instruct jockeys riding horses with a history of moderate to severe EIPH to refrain from racing in this manner.    What is the effect of a one-off diagnosis of EIPH over a horse’s career?    A pattern of increasing endoscopic EIPH severity over a racehorse’s career is suspected but has not been proven. Another Australian research group examined 744 thoroughbreds post-race with endoscopy, looked back 12 years later and compared EIPH score to their career performance. There was no association between any grade of EIPH and career duration, lifetime earnings, or the number of wins or places. These observations led to the conclusion that a one-off diagnosis of EIPH is an unreliable predictor of overall career performance.    Is EIPH a progressive disease?    <<Fig 5 near here>>  EIPH is typically described as a progressive disease, but again, evidence is lacking. In our Australian thoroughbred population, EIPH scores were often erratic from one race start to the next, especially as the EIPH severity increases. We were able to identify factors which were associated with change in EIPH score from one race start to another and which might help manage horses that are prone to EIPH. Increasing the number of days between races was associated with a transition from a higher to a lower grade of EIPH and racing in cooler weather was associated with a transition from a lower to a higher EIPH grade at the next observation. There are also likely to be unmeasured intra-horse and race factors that could also account for the variation in EIPH scores from one race start to another.   Although in individual horses, EIPH severity can differ from race to race, from a population perspective, we concluded that EIPH is a mildly progressive condition.    What are the risk factors for EIPH?    Several investigators have found an association between temperature and EIPH. Cold weather on race day increases the chances of diagnosing EIPH and increases the chances of diagnosing more severe grades of EIPH. Furthermore, for horses that previously had no or only mild EIPH, racing in colder weather was more likely to be associated with a worsening of EIPH grade at the next observation. The reason that EIPH worsens with cold weather is unknown, but this phenomenon could mimic cold-induced pulmonary hypertension reported in other species. It may reflect the ambient temperature during training rather than specifically the temperature at the time of the race. Avoiding cold weather during training or racing may reduce the risk of EIPH in horses with a history of moderate to severe EIPH.  Lifetime starts was a predictor for EIPH risk in our studies; a stronger risk was the number of races in a current racing preparation reflecting a straightforward, short-term cumulative association between EIPH and racing. Trainers frequently recognize that horses with EIPH perform well ‘fresh’, meaning that they perform at their best early in a racing preparation. From a management point of view, limiting the number of races in a racing preparation for horses prone to EIPH could reduce disease severity.  No studies have identified an association between EIPH and sex, altitude or racetrack surface. Other factors that have been investigated such as track firmness and race distance have mixed results in the literature. In Australia bar shoes are typically used when horses have short-term foot problems. We found that the application of one or more bar shoes increased the risk of EIPH and severity in our racing population. The reason for this is unknown, but it may not be a direct effect of the shoes; instead we speculated that subclinical hoof pain could increase cardiovascular pressures during racing. We found horses wearing bar shoes were less likely to collect prize money, collected less prize money and finished further behind the winner than horses racing in standard plates. Trainers and vets should reconsider or delay racing a horse that requires a bar shoe for a short-term foot issue.     In conclusion, from our studies looking at EIPH in Australian racehorses, our key findings were:  Endoscopy is the preferred method of detecting EIPH and should be performed 30-120 minutes after racing;  Horses prone to moderate or severe EIPH should avoid racing or training during the colder months;  Trainers should consider changing the riding tactics of horses with severe EIPH, settling the horse in a mid-field or back marker position;  The number of races in a racing preparation should be limited for horses with EIPH;  It is helpful to increase the interval between races for horses with severe EIPH;  It is prudent to reconsider or delay racing a horse a short-term foot issue rather than use a bar shoe.     EVJ papers to link   Crispe EJ, Lester GD, Robertson ID, Secombe CJ. Bar shoes and ambient temperature are risk factors for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses.  Equine Vet J . 2016 Jul;48(4):438-41.  https://onlinelibrary.wiley.com/doi/abs/10.1111/evj.12458      Crispe EJ, Lester GD, Secombe CJ, Perera DI. The association between exercise-induced pulmonary haemorrhage and race-day performance in Thoroughbred racehorses.  Equine Vet J . 2017 Sep;49(5):584-589.  https://onlinelibrary.wiley.com/doi/full/10.1111/evj.12671      Crispe EJ, Lester GD, Secombe CJ, Perera DI, Manderson AA, Turlach BA, Lester GD, Exercise-induced pulmonary haemorrhage in Thoroughbred racehorses: a longitudinal study.  Equine Vet J . 2019 Jan;51(1):45-51.  https://onlinelibrary.wiley.com/doi/abs/10.1111/evj.12957

By Ellie Crispe and Guy Lester

 

Exercise-induced pulmonary haemorrhage (EIPH) is a common disease of racehorses. The precise cause of EIPH is yet to be fully determined, but a well-accepted theory is that lung blood vessels rupture in response to the extremely high blood pressure and low airway pressure experienced during strenuous exercise. The barrier that separates the airway from the blood vessels is ultra-thin to facilitate the efficient exchange of gases, but this predisposes to breakage. The condition is most frequently described in Thoroughbred and Standardbred racehorses, but it has also been identified in racing Appaloosas and Quarter Horses, as well as horses involved in other high intensity athletic activities, including showjumpers, 3-day eventers, barrel racers, steeplechasers and polo horses.

EIPH is not unique to horses and has been reported in human athletes, as well as racing greyhounds and camels. Our group at Murdoch University in Perth Australia has had an interest in EIPH, which has led to three recent publications in the Equine Veterinary Journal.1-3

How common is EIPH?

Fig 1.jpg

Blood from both nostrils—also known as epistaxis—is the most obvious manifestation of EIPH and occurs between 1.5 and 8.4/1000 race starts, varying with racing jurisdiction. Epistaxis represents a severe manifestation of EIPH, and basing surveys on its presence vastly underestimates the true prevalence of lung haemorrhage. There are several techniques used to diagnose EIPH, but endoscopy of the trachea 30-120 minutes after racing or galloping is a common and reliable method. Occurrence and severity of pulmonary haemorrhage is typically graded using a 0-4 scale. Using endoscopy, we reported a prevalence of EIPH post-race in Australian thoroughbreds racing on turf tracks of around 55%, with most positive horses having low to moderate volumes of blood in the trachea. EIPH is less common if horses are examined after trialling, and reduced further if examined after track gallops. The prevalence of EIPH increases when horses are examined on multiple occasions after racing, and in fact all horses in our research population that had seven monitored race-starts experienced EIPH on at least one occasion.

What is the effect of EIPH on race-day performance?

It is generally considered that EIPH has a negative impact on racing performance, but evidence for this assertion is surprisingly lacking. We performed 3,794 post-race endoscopy exams on over 1,500 Australian horses and reported that inferior race-day performance was limited to horses with severe EIPH (grades 3 and 4); this reflected only 6.3% of all examinations. Horses with the highest grades of EIPH (grade 4) were less likely to finish in the first three, finished further from the winner, were less likely to collect race earnings, were slower over the final stages of the race, and were more likely to be overtaken by other competitors in the home straight than horses without EIPH. Interestingly, horses with EIPH grade 1 or 2 were more likely to overtake others in the home straight, compared to horses without EIPH (grade 0).

Screen Shot 2019-03-21 at 11.31.49.png

It is highly unlikely that low-grade EIPH (grade 1 or 2) confers an athletic advantage; a plausible explanation is that horses that are ridden competitively to the finish are functioning at their maximal physiological limit, compared to horses that are eased up, and overtaken, during the finishing stages of the race because they are not in prize contention or are affected by interference in the home straight.  Another interesting finding was that horses with moderate to severe EIPH (grades 3 or 4) raced the early and mid-sections of the race faster than horses without EIPH. It is possible that these horses reach the breaking threshold of the small lung blood vessels at an earlier stage in the race compared to horses that start the race slower, compounding the severity thereafter. A study of barrel racing horses reported that horses with the most severe grade of EIPH were faster than horses without EIPH, a finding which may also reflect this rapid acceleration increasing the risk of EIPH. It may be wise for trainers to instruct jockeys riding horses with a history of moderate to severe EIPH to refrain from racing in this manner.

What is the effect of a one-off diagnosis of EIPH over a horse’s career?…

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