EIPH occurs world-wide in more than 80% of Thoroughbred and Standardbred racehorses, and is also seen in Quarterhorse racehorses and polo ponies. Horses that exercise at high intensities are more likely to suffer from EIPH. This condition is relatively uncommon in horses used for less intense activities, including endurance events, regardless of duration. The prevalence of EIPH has been found to increase with age, but there is no difference between males and females.
Whilst EIPH is extremely common in racehorses, actual bleeding from the nose (epistaxis) is a relatively rare sign, occurring in only 1-2% of equine sufferers. More commonly, bleeding is restricted to deep within the lungs and can only be detected by endoscopic exploration of the airways following exercise. The clinical signs of low grade EIPH are vague; some horses show no signs, others may swallow during racing, cough, swerve or veer, or have a sudden decrease in running speed. In many cases these signs may be overlooked and simply attributed to a poor performance. Extremely rarely, the haemorrhage is severe enough to cause collapse, severe distress or death.
There are many theories regarding the causes of EIPH. The favoured theory at present is that under intense exercise blood vessels in the lung can fail and blood passes into the airways. The failure occurs because the walls of blood vessels in the lung are thin in order to effective transfer of oxygen, but this means their walls and weak and are unable to cope with the more than doubling of blood pressure that occurs during intense exercise. It is the upper part of the lung, where there is the greatest pressure difference between the blood vessels and airways, that bleeding most commonly occurs. The uppermost part of the lung is also subjected to extra pressure, as force is transmitted to this region when the racing horse lands on their forelegs.
As mentioned EIPH is commonly associated with exercise intolerance, which can be the direct result of the blood in the airways. However, studies have shown that blood in the airways sets off an inflammatory reaction which leads to the formation of scar tissue. Scar tissue is not as flexible as healthy lung tissue and more and more is formed with each rupture. As this builds up, the ability of the affected part of the lung to expand and contract is decreased and so is the ability to ventilate. The horse, which naturally develops low oxygen levels during exercise, becomes even more compromised and exercise intolerant. In addition, at the point where scarred lung meets healthy lung, there is extra tension and the area is more prone to haemorrhage. EIPH can therefore be seen as a progressive disease that gradually affects more and more lung tissue, hence the condition worsens with training and age. It is likely that horses with moderate or more severe EIPH will never perform to the potential their owner might expect, but that is not to say none will do well. Those with epistaxis are likely to lose days of training and/or racing as they must be given time to recover.
There is no treatment for EIPH; the disease can only be managed. As a minimum, stables with good ventilation should be provided in order to help alleviate the respiratory distress that an EIPH horse may experience after exercise. Ideally EIPH horses should be subjected to high intensity exercise as little as possible, but this is very rarely a viable option. Instead attempts can be made to minimise the haemorrhage and subsequent airway inflammation.
There are no drugs licensed for treatment of EIPH. Presently only one drug is routinely used – Frusemide is a diuretic; it acts to increase water loss in urine and so decrease the blood volume and blood pressure. There is reasonable evidence that Frusemide treatment before training decreases the severity of haemorrhage, and as such limits the progressive damage. Horses are however not permitted to race on Frusemide so its use is limited to training.
Other possible therapeutics are currently being investigated. It is thought that administration of corticosteriods by aerosol may minimise the inflammatory damage after a bleed has occurred, and so potentially lengthen the working life of the horse. By administering the corticosteriods via aerosol it is hoped the systemic complications will be avoided. The second groups of drugs presently being studied are vasodliators, which may decrease the blood pressure in lung blood vessels of resting horses. It is hoped that the same will occur in horses at exercise. It must be noted that neither aerosol corticosteriods nor vasodliators have been used clinically and so are merely potential future EIPH therapies.
Some American literature describes the use of some less scientific remedies. Manufacturers of some herbal concoctions claim that their products can control bleeding, strengthen vessels and encourage healing. Also a ‘FLAIR’ strip is being marketed, the claim being that this nasal strip makes breathing easier and somehow reduces bleeding associated with EIPH. The value of such products should probably be considered with caution, their true value with management of EIPH being questionable.
Severe cases of epistaxis my need to be given an oxygen supply, and should always be given antibiotics to protect against any secondary infection.
If you suspect your horse may be suffering EIPH or any other disease contact your veterinary surgeon for a proper diagnosis and the best advise on how to manage YOUR horse. Remember - every case is different.