EIPH: Bleeding in Racing Horses and Camels

Exercise-induced pulmonary haemorrhage is bleeding into the airways during intense exercise. On endoscopy, some degree of it is present in the majority of horses working at racing speed. Visible bleeding at the nostrils — epistaxis — occurs in only a small percentage, which is why EIPH is far more common than it appears.

The mechanism

The cause is mechanical. At galloping speed, pulmonary capillary pressures rise dramatically while alveolar pressure swings in the opposite direction during breathing. The pressure differential across the blood-gas barrier — a membrane roughly half a micron thick — exceeds what it can withstand, and capillaries rupture.

This is called stress failure of pulmonary capillaries, and it is a consequence of the extraordinary cardiac output these animals generate. It is not primarily an infection, a clotting disorder or a weakness.

Contributing factors that make it worse:

• Higher speed and longer duration of maximal effort
• Existing lower airway inflammation
• Cold, dry or dusty air
• Prior EIPH episodes — the remodelling that follows bleeding predisposes to more

Grading

Post-exercise endoscopy, ideally 30 to 90 minutes after work, graded 0 to 4:

• Grade 0 — no blood visible
• Grade 1 — one or more flecks, or a narrow stream covering less than a quarter of the tracheal surface
• Grade 2 — one long stream, or several short ones covering more than a third
• Grade 3 — multiple streams covering more than a third of the tracheal surface
• Grade 4 — multiple coalescing streams covering the whole surface, with blood pooling

Bronchoalveolar lavage cytology showing haemosiderophages indicates bleeding in the preceding weeks even where endoscopy is clear.

Management, and the regulatory reality

Furosemide reduces EIPH severity in controlled studies. It is also prohibited on race day in most of the world, and in the jurisdictions that permit it, it is under a declared and supervised programme with a defined administration window. Several authorities prohibit it entirely. Its use is a regulatory question before it is a clinical one, and the answer depends entirely on where you are racing.

Treating concurrent airway inflammation is the intervention with no regulatory complication attached. Inflammatory airway disease is extremely common, it worsens EIPH, and it is treatable.

Environmental management — dust control in bedding and forage, ventilation, avoiding work in the worst air quality — is unglamorous and genuinely effective.

Rest after a significant bleed. The lung needs time to remodel. Racing an animal through repeated grade 3 and 4 episodes produces progressive, permanent change.

Nasal strips reduce upper airway resistance and have modest supporting evidence. Permitted under most rulebooks; check yours.

Antifibrinolytics such as tranexamic acid are used by some practitioners. The evidence base in EIPH specifically is thinner than for furosemide, and they are controlled medications under most rulebooks.

Camels

EIPH is documented in racing camels, and the underlying mechanism is the same. The literature is much smaller, the endoscopic grading systems are adapted from equine work, and treatment protocols are largely extrapolated. Work with a veterinarian experienced in camel racing rather than applying equine protocols directly.

The welfare question

A grade 4 bleeder is telling you something. Repeated severe episodes cause progressive lung remodelling and fibrosis, and the animal's future depends on that being recognised.

Some animals should not be racing. Recognising which ones is part of the job, and it is not a conversation that gets easier by being deferred.