How prevalent is EIPH?

Exercised-Induced Pulmonary Hemorrhage (EIPH), also known as bleeding, occurs during strenuous exercise and is common in racehorses. However, blood appears in the nostrils (epistaxis) in only a small percentage of cases. In Victoria, Australia, the prevalence of horses bleeding for the first-time (defined as the appearance of blood in both nostrils after exercise) is about 1.5 for every 1000 starters, or 0.15%. This result is comparable to the percentage reported in Japan, Britain, and South Africa; and less than that reported in Singapore, Hong Kong, and the USA. Although blood appearing in the nostrils is relatively uncommon, data from large surveys performed in several areas around the world suggest that some degree of EIPH occurs in up to 75% of runners. Blood may be present in only the trachea and, therefore, only evident on endoscopic examinations after exercise. As it takes time for the natural clearance mechanism of the respiratory tract to move blood from the lungs into the trachea, an endoscope may not reveal any hemorrhaging unless it is performed 60 minutes or more after exercise. In some cases, EIPH may not be evident in an endoscopic examination and a laboratory analysis of a bronchoalveolar lavage sample (BAL or ‘lung wash’) is necessary to demonstrate its occurrence.

Why do horses bleed from their lungs?

Although EIPH is common, the cause of it is not yet fully understood. Some theories include capillary stress failure in the lungs, pulmonary fibrosis (preexisting scarring in the lung tissues) and small airway disease (inflammation triggered by viral infections or inhalation of stable dust and other foreign particles). Currently, the most accepted theory is that of exercise-induced pulmonary hypertension resulting from alveolar-capillary stress failure. The alveoli-capillary membrane is extremely thin to allow respiratory gases such as oxygen and carbon dioxide to be exchanged. Evidence suggests that EIPH is caused when the internal pressure of the lungs rises to too high of a level and causes the membrane barrier to fail. When galloping, racehorses have a very high cardiac output that pushes blood through the lungs at a high rate. This output creates high pressure in the pulmonary capillaries that may cause ruptures, releasing blood into the alveoli of the lungs. Furthermore, the large negative respiratory pressure in the airways that allows for high airflow contributes to the pressure differences placed on the capillary walls. Any upper respiratory tract obstruction (such as laryngeal hemiplegia) or airway disease in the lungs may exacerbate the large negative pressure and potentially contribute further to EIPH. Another hypothesis put forward as a contributing factor to EIPH may be an impact-induced injury to the lungs caused by ground-strike pressures during galloping. These impacts produce pressure waves that are transmitted through the forelimbs, shoulder blades, rib cage, and eventually the lungs. Although some studies suggest that EIPH occurs more frequently on harder tracks, other studies have not found this to be a factor. However, evidence that horses can bleed while swimming, an exercise that does not create ground-strike impacts, shows that this is not necessarily the cause of the problem. Recent research proposes that increased pressure in the veins in lung tissue may result in veno-occlusive remodeling, narrowing the lumen of the veins similarly to how humans are affected by veno-occlusive disease (PVOD). A better understanding of the cause of this condition continues to be sought in the hope that it will lead to improved means of prevention of EIPH.

Does EIPH affect performance?

Horses that bleed from the nose have a clear reduction in performance. Horses with blood in both nostrils typically finish worse than those in midfield, and about half of these horses finish last. The effect of EIPH on performance is related to the volume of hemorrhaging. A small amount of blood may not significantly reduce performance, but a large amount of bleeding can. The effects of bleeding are likely to be progressive and lung damage cumulative, ultimately leading to significant decreases in performance. This is because the blood causes pulmonary inflammation for at least three weeks following each episode. Blood is cleared from the lungs slowly, and repeated sessions of exercise may result in repeated episodes of EIPH. Hence, EIPH is a serious condition in racehorses and prevention or reduction of its incidence is an important issue.

How many horses die as a result of bleeding?

The answer is very few. A review of causes of death in horses at several centers in Australia and the USA revealed that less than 2% of deaths are due to severe EIPH (‘bleeding’), a small percentage due to cardiovascular disease, and the majority of fatalities are a result of serious musculoskeletal injuries. Between 1999-2005, 6 horses collapsed and died during races in Singapore for reasons other than musculoskeletal injury. Of these, necropsy examination confirmed 3 of the horses died from severe EIPH (i.e., 3 cases in over 30,000 runners during this period), 1 due to heart failure, 1 due to a rupture of a major internal vessel, and in 1 case where the cause could not be determined. Furthermore, it can be said that of the 218 bleeders reported after racing during this same period, only 3 died. Horses that suffer a severe or fatal bleed during exercise typically weaken and stumble before they ‘pull up’ or collapse, usually allowing time for the jockey to jump off in many cases. Serious injuries to riders are more likely to be associated with catastrophic musculoskeletal injuries and other accidents when a horse falls or veers suddenly and unexpectedly.

What are the rules regarding bleeders?

Although individuals may differ slightly in their opinions, overall, the parties concerned (trainers, owners, jockeys, vets, and stewards) seem generally satisfied with the current rules. Consequences may vary from no limiting action to outright banned from racing after the second episode. The pre-race administration of furosemide (‘Lasix’) is permitted in some states in the USA, but nowhere else. Although trainers may want furosemide permitted, there are important reasons why it is not. In the United Kingdom, there are no specific rules relating to horses exhibiting blood in the nostrils after exercise. In many jurisdictions, the problem tends to be self-regulating, with many trainers voluntarily retiring most horses that repeatedly bleed. However, this does not obviate the need for regulation. The Rules of Racing in Australia are designed to significantly protect the health and welfare of both horses and jockeys. If a horse is observed by officials to have bled from one or both nostrils after exercise or post-race, the restrictions are no racing for 180 days; with the fourth episode resulting in the horse being banned from competition for life. In South Africa the rule stipulates: the first episode bans a horse from racing for 3 months, the second episode bans a horse from racing for 6 months, and the third episode bans a horse for life. Under the Rules of the Malayan Racing Association, a horse declared as a bleeder must not be cantered or galloped on the main training tracks for 2 months, or start in any race for 3 months, and only then after completing a 1000m trials gallop with bleeding. If the horse races 3 times without bleeding it will revert to being at a non-bleeder status. If the horse does bleed again before achieving this, it must not be cantered or galloped on the main training tracks for 2 months or start in a race for 6 months, and only then after completing a 1000m trial gallop without bleeding. Again, if the horse then races 3 times without bleeding it will revert to non-bleeder status. The horse is permanently banned if it suffers a 3rd bleeding attack without having reverted to non-bleeder status. The regulations for bleeders are stricter in Australia, New Zealand, and Hong Kong. In Australia and New Zealand, horses reported by officials to have blood in both nostrils (unless in the opinion of the Stewards such as when bleeding is caused by external trauma) may not be exercised on any racecourse for 2 months or start in any race for 3 months, and only then after a satisfactory gallop of at least 1,000m in the presence of a Steward. If the horse bleeds on a second occasion, it is banned for life. In Hong Kong, the rule states that the first episode bans the horse from the training track for 2 months and from racing for 3 months only after passing a barrier trial. The second episode bans the horse for life.

Can bleeding be prevented or managed?

Since hemorrhages in the lung can create severe and continuing pathologic reactions, it is well worthwhile to investigate any possible predisposing causes of EIPH in any individual horse and to implement strategies to reduce the occurrence and severity of this condition where possible. There are currently no methods and treatments which directly prevent the occurrence of EIPH. However, certain treatments and management strategies can assist in reducing the severity of hemorrhaging and thus reduce the ongoing repetitive lung damage. Ideally, treatment includes management of the damage already present in the lungs by providing them with sufficient time to clear blood and to heal. This usually requires a collection of lung washes which is best performed several weeks after the bleeding episode. A minimum time of 1 month is likely to be needed to recover from a single acute episode of EIPH. A longer period is required in many cases where chronic lesions are present. Despite months of rest and treatment, some horses do continue to bleed when more strenuous exercise resumes. These horses should be and usually are retired. The management of horses with EIPH is aimed at reducing bleeding. Furosemide (Lasix) used before strenuous exercise may decrease the severity of EIPH, but it does not prevent it from occurring. When given 1.5-4 hrs before exercise, this diuretic drug produces a decrease in pressure in the blood vessels of the lungs. Horses treated with this diuretic effect tend to lose large amounts of water, weigh less, and race faster. For this reason, the unwanted effects of the detection of other drugs, and the fact that furosemide is not effective in preventing EIPH, most racing authorities do not allow the use of this drug before racing.

What is the best way to manage EIPH?

Ensuring good stable management practices is essential for the maintenance of respiratory health. Considerations should include the design of stables which should provide good ventilation, provisions of dust-free feed and bedding, feeding horses off the ground where possible, and allowing as much paddock time as possible. Employ sound training practices such as the appropriate conditioning of horses, training with knowledge of the factors that may increase the risk of bleeding (for example, strenuous exercise on an inclined treadmill), and training in such a way that these factors have a smaller impact on at-risk horses. Depending on the circumstances and diagnosis in each case, therapy with appropriate corticosteroids and/or bronchodilators amongst other things may be prescribed by the veterinarian to treat the underlying condition. Diagnose and treat any conditions causing upper respiratory tract obstruction (such as dorsal displacement of the soft palate). Ideally, resting horses for an appropriate period of time following an episode of EIPH provides the opportunity for blood to clear and the lungs to heal.

References

Steele, Cate. An Update on “Bleeders” and EIPH. Racing Victoria, 7AD,
     www.racingvictoria.com.au/the-horse/veterinary-
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