Exercise Induced Pulmonary Haemorrhage (“Bleeders”)

Many people involved with athletic horses will have come across a horse that is diagnosed as a “bleeder” at some stage, though many are unsure about what this actually entails or the best way to manage them.

“Bleeding” refers to racehorses bleeding into their lungs during a race or fast work. Blood may be seen at the nostrils following hard exercise and if this occurs at the races it may lead to a temporary or permanent ban on that horse racing. More often, no blood is seen externally and other methods must be used to see if it has occurred.

Diagnosis of bleeding can be made either by endoscopy performed within an hour of fast work or by lung wash which will reveal the presence of blood up to two weeks after a bleeding episode has taken place.

The incidence of bleeding relates to the speed of exercise and increases with age and distance. It is seen both in winning horses and those that perform badly, however experiments have shown that even small amounts of blood can hamper performance.

Bleeding is believed to occur due to the extreme difference in pressure between the small blood vessels in the lung (high pressure 70-90 mmHg) and the negative pressure within the air space (low pressure -30mmHg). As the tissue between blood vessels and airspace is extremely thin to allow oxygen exchange, this pressure difference causes “blow outs” of the vessels and allows free blood to enter the lungs.

The damaged vessels, and the blood itself, initiate an inflammatory response in the lungs. This inflammation encourages further bleeding and a destructive cycle results, leading to impaired performance.

“Bleeders” are not really cured but many are managed quite effectively. Management methods vary but include such things as spacing races to give lung tissue time to recover in between episodes, not swimming these horses, minimising dust and other airway irritants etc.

Medications can be helpful in treating these horses but their use is restricted by the need to observe racing withdrawal times and present horses free of medication on race days. Medications commonly used to treat bleeders include diuretics to decrease intravascular pressure, anti inflammatories to decrease airway irritation, bronchodilators in an effort to decrease negative inspiratory pressure, vitamin supplements marketed to increase vascular strength etc.