Bleeding in the Lungs: What EIPH Does to Racing Performance

A horse finishes a race, and a trickle of blood appears at one nostril. It looks dramatic, and it is the version of pulmonary bleeding everyone recognises. It is also the rarest version by far.

Put an endoscope down the airway of racehorses 30 to 60 minutes after they run, and blood is found in the trachea of 45 to 75 per cent of them. Wash the deeper airways and examine the fluid under a microscope, and evidence of haemorrhage turns up in more than 90 per cent. Visible bleeding from the nose happens in a small minority. Almost all of it is invisible from the outside.

What exercise-induced pulmonary haemorrhage actually is

EIPH is bleeding into the lung that happens because of the intensity of exercise itself, not because of infection or injury.

The mechanism is mechanical. During maximal exercise a racing horse moves an enormous volume of blood through the lungs, and pressure in the pulmonary capillaries rises steeply. The barrier between a capillary and the air space it serves is astonishingly thin — it has to be, for oxygen to cross it. Under enough pressure that membrane physically fails. Blood crosses into the alveolus.

This is not a defect in a particular horse. It is a consequence of an animal built to move blood and oxygen faster than the tissue separating them can comfortably withstand. That is why the numbers are so high across whole populations rather than clustering in a few individuals.

Why it matters for performance

An alveolus with blood in it is not exchanging gas. Repeated episodes leave inflammation and, over time, scarring in the affected regions of the lung, which are typically the caudodorsal areas.

The practical signal is rarely dramatic. It looks like a horse that finishes a length or two behind where it should, that takes longer to recover its breathing after work, that coughs after exercise, or that swallows repeatedly on pulling up. Severity graded on endoscopy correlates with poorer finishing positions.

Diagnosis: you cannot see it from the stands

Because epistaxis is the exception rather than the rule, EIPH is diagnosed by looking:

• Videoendoscopy performed 30 to 60 minutes after racing or hard work, with the amount of blood in the trachea graded on a 0 to 4 scale. This is the standard field method.
• Bronchoalveolar lavage, in which fluid is washed into the lower airway and recovered for examination. Far more sensitive: it detects red blood cells and the iron-laden cells that indicate earlier bleeding, and picks up horses that look clean on endoscopy.

Timing matters. Scope too early and blood may not yet have moved up the airway; scope too late and it may have been cleared. The 30 to 60 minute window exists for a reason.

Furosemide: what the evidence supports, and what it does not

Furosemide is the most widely used medication in this context, and the honest summary is more qualified than the marketing around it.

How it is thought to work: by reducing pulmonary arterial and left atrial pressures, it lowers the pressure across the capillary wall during exercise, and so reduces the mechanical stress that causes the membrane to fail.

What studies show: furosemide does not prevent EIPH. Horses given it still bleed. What the evidence supports is a reduction in severity — lower endoscopic grades and lower red cell counts in lavage fluid compared with untreated horses. Timing appears to matter: endoscopic scores were lower when furosemide was given four hours before high-speed work than at twenty-four hours.

So the accurate framing is a drug that reduces how much a horse bleeds, not one that stops it bleeding. Anyone selling it as prevention is overstating the case.

The regulatory position is changing. Race-day furosemide has been restricted or prohibited in a growing number of jurisdictions, and rules differ sharply between countries and between race types. This is one of the areas where “what everyone does at home” and “what is permitted here” diverge most, and the penalty falls on the trainer. Check the rules of the specific body governing your race before planning any treatment.

What else actually influences it

Medication is one lever among several, and the others are less discussed because nobody sells them:

• Intensity. EIPH is a function of how hard the horse works. Breezing and racing produce it; steady canter work largely does not.
• Airway inflammation. Horses with underlying inflammatory airway disease tend to bleed more. Dust in bedding and forage, poor ventilation and ammonia in the stable all feed that inflammation, and all are fixable.
• Recovery time. A lung that has bled needs time before the next maximal effort. Racing a horse back too quickly stacks damage on damage.
• Respiratory infection. Working a horse through a viral or bacterial airway infection increases both inflammation and risk.
• Cold weather has been associated with higher severity in several studies.

A yard that soaks or steams hay, improves ventilation, keeps ammonia down and respects recovery intervals is doing something about EIPH every day, without a syringe.

What this means for camels

The research base for EIPH is overwhelmingly equine. Racing camels work at high intensity over long distances and the same physiological pressures apply in principle, but the published evidence on prevalence, severity and treatment response in camels is thin by comparison. Treat equine figures as a guide to the mechanism, not as numbers that transfer directly, and rely on your veterinarian’s assessment of the individual animal.

The short version

Most racehorses in hard work bleed into their lungs to some degree, and almost none of it is visible. It costs performance and, repeated often enough, damages lung tissue. It is diagnosed by scope or lavage, not by watching for a bloody nose. Furosemide reduces severity rather than preventing it, and is increasingly restricted on race day. Air quality, workload and recovery time do more of the work than most people give them credit for.

This article is general information about a condition, not veterinary advice, a diagnosis or a treatment plan. EIPH should be assessed by a veterinarian, and any medication, its dose, its timing and its legality under the applicable racing rules must be determined with the veterinarian attending the individual animal.