Kate Hore RNutr(Animal). Snr Nutritionist at NAF
Exercise Induced Pulmonary Haemorrhage, EIPH, is a disorder which is commonly attributed to capillary damage at maximal exercise, causing bleeding. It is most often found in horses who are working at peak performance, such as racehorses, polo ponies or eventers. Studies have shown that between 1 and 2% of racehorses bleed from the nostrils after a race, however when using endoscopy as many as 60% show evidence of bleeding.
But the question remains, what causes this bleeding? Unfortunately this is the source of much debate, despite us having been aware of the issue for nearly 300 years. Research suggests that this is related to an imbalance in heart rate during high intensity exercise, which essentially increases pressure in the capillaries of the lungs, causing them to rupture. Some research points toward obstruction to the upper airway due to roaring is another contributing factor to EIPH. This may cause the pressure gradients to be more extreme, causing more severe tears.
Research studies show the horse's heart does not relax quickly enough between beats during intense exercise, when heart rate can approach 230 beats per minute. When the left side of the heart is insufficiently relaxed, greater pressures within the lung are required to facilitate blood flow from the lung to the heart between beats. This "back-pressure" places strain on the fine-walled pulmonary capillaries and some break, releasing blood into the airways.