Is it not that unusual to see a horse with blood in both nostrils following a session of fast work, whether during training or after a race or competition. This is not technically a true nosebleed as the blood coming up from the lungs.

Exercise-induced pulmonary haemorrhage (EIPH) refers to bleeding (haemorrhage) from the blood vessels within the lung (pulmonary). Horses that suffer with this are sometimes called “bleeders” or described as having “burst blood vessels”.

The use of modern flexible endoscopes has helped vets understand what is happening. Passing an endoscope up the horse’s nose has allowed us to see inside and prove that the blood does originate from the lungs.

It is now understood that the tiny thin-walled blood vessels (pulmonary capillaries) in the lungs are damaged by the huge air and blood-flow demands associated with the galloping horse, resulting in bleeding into the lungs.

Signs to watch for include:

  • A nosebleed, usually from both nostrils, after exercise
  • Coughing
  • Poor exercise performance

In severe cases, bleeding is sufficient to well up through the airways and appear at the nostrils, but in most cases the blood is reabsorbed or swallowed and not seen as a nosebleed. Very rarely a horse may sustain a fatal bleed from the lungs, generally towards the end of a race or the cross-country phase of a competition.

As EIPH may affect performance, particularly in racehorses — about one in 1,000 horses racing in the UK end up with noticeable bleeding at the nostrils — it has attracted a lot of research effort, but it is not only racehorses that are affected.

Following intense exercise, all horses break some of the smallest blood vessels in their lung. EIPH can also affect horses used for cross-country, polo and show jumping, as well as some draught and endurance horses.

The chances of EIPH are known to increase with:

  • Speed of exercise
  • Age of horse
  • The presence of any kind of disease of the lower airways, such as stable coughs and dust allergies
  • Abnormal blood clotting
  • Upper airway obstruction, shown as roaring or gurgling

The treatment of horses that have had episodes of EIPH includes rest and anti-inflammatory medication, such as bute. A gradual return to exercise is usually recommended, together with efforts to ensure good air hygiene to reduce small airway inflammation.

Frusemide (brand name Lasix or Salix) is a popular treatment, but is banned for Thoroughbred racing in the UK, despite being used widely in the USA.

The use of nasal strips has recently been shown to help by making it significantly easier for horses to breathe during periods of strenuous exercise. Such devices are banned for UK Thoroughbred racing, but have been seen in use on many successful competition horses.

This article formed part of a veterinary feature first published in Horse & Hound (24 November 05)