After lameness, respiratory problems are the main reason for horses performing below expectations. According to Marlin and Nankervis (2002) exercise-induced pulmonary haemorrhage (EIPH) is probably the most common abnormality affecting the horse during training.
EIPH in racehorses dates back to the 18th century, Bleeding Childers was one of the first documented ‘bleeders’ and was retired to stud because of frequent bleeding episodes (Erickson et al., 2000). Although it has since been well documented that a small percentage of racehorses show blood at the nostrils after racing, it was not until fibre-optic endoscopes were used in the 1970’s that the blood was found to originate from the lungs, rather than the upper airway (Marlin & Nankervis, 2002). The technique of bronchoalveolar lavage (BAL) has brought even more refinement to the detection and measurement of EIPH. With this technique, a small amount of fluid is injected into the lungs and then aspirated out to obtain samples of cellular debris & blood (Jones, 2003).
Despite the knowledge that horses bleed in their lungs after intense exercise, the cause is still not known. The most popular theory is that when the horse is exercising heavily a huge increase in blood pressure occurs, forcing blood out through the lung capillary walls and through the thin membrane that separates them from the alveoli (Jones, 2003).
Any breed or type of horse or pony undertaking strenuous exercise may experience some degree of EIPH. The condition has not only been observed in Thoroughbreds following flat racing and steeplechasing, but also in horses used for polo, showjumping and cross-country. Also, recent research in Japan has shown that EIPH can even occur at slow canter (Oikawa, 1999; cited Marlin & Nankervis, 2002).
Although many trainers and veterinary surgeons believe that EIPH affects performance this has not been proven in scientific studies. However, the process of blood entering the airways can have both immediate and long-term potential effects. It is known that EIPH only affects a small amount of the total lung, but in the short term EIPH is likely to impair ventilation and gas exchange at the affected parts. In the long term as the damaged tissue is repaired there is likely to be some fibrosis and stiffening of the lung tissue, or loss of tissue structure causing the damaged area not to function fully (Marlin & Nankervis, 2002).
Because the condition is not well understood, a wide range of treatments are currently in use including antioxidants, anticoagulants, aspirin, blood removal, hormones, diuretics, bronchodilators, water deprivation and nasal strips.
The equine nasal strip was invented by two equine veterinarians following the success of the nasal strip for human athletes in promoting easier nasal breathing during exercise (Erickson et al., 2000). The principle behind the use of nasal dilator strips is that the nasal passages are held open so that more oxygen can enter the lungs in a shorter period of time, decreasing the stress on pulmonary capillaries (Marlin & Nankervis, 2002). Several studies have been carried out since the introduction of equine nasal strips to determine the efficacy of the strip in reducing the occurrence and severity of EIPH.