A trickle of blood from a horse’s nostril may not seem that concerning, but it can be the first indication of serious medical problems.
The most life-threatening condition is a fungal infection of the carotid artery, which is a major vessel that supplies blood to the brain.
A brief anatomy lesson is necessary to understand the severity of this infection. The paired carotid arteries course through an air-filled out-pouching of the eustachian tubes, which connect the mouth to the ears.
These guttural pouches are located in the head at the level of the inside of the jaw on each side.
In addition to the carotid artery, several other important structures travel through the guttural pouches, including a small bone that suspends the tongue and nerves.
The purpose of the guttural pouch is unknown. Speculation is that these air-filled sacs cool the blood entering the brain, especially during exercise, offering it protection from heat injur y. Since evolution has selected horses to be flight animals, this adaption to enhance athleticism makes sense.
Guttural pouches can also harbour the bacteria responsible for strangles long after clinical signs resolve. These carrier horses are suspected to be a source of infection to unvaccinated or naïve horses.
The fungus involved in these guttural pouch infections is most commonly Aspergillis. It normally lives in dirt, but how it causes infection in horses is unknown.
Symptoms and treatment
Clinical signs of guttural pouch fungal infection include opaque nasal discharge, nosebleeds and neurologic dysfunction (trouble swallowing or droopy face).
Examination of the pouches is necessary for diagnosis and involves passing an endoscope through the nose and into the pouch. This small fibre optic camera can see fungus growing on the vessels within the pouch.
Left untreated, sudden fatal bleeding can result if the fungus erodes the vessel wall. Nerve damage and bone infection can also occur.
Treatment involves permanently clamping off the vessel, which presumably stops the supply of nutrients to the fungus, effectively killing it. It also decreases the chance of a fatal bleed.
Another cause of nosebleeds in horses occurs after bouts of intense exercise. Some horses experience bleeding from the airways in the lungs, which is called exercise-induced pulmonary hemorrhage.
Racehorses are most commonly affected, but any performance horse can suffer from this disease. Although not fully understood, the cause is suspected to be weakening of the smallest blood vessels from stress.
Blood can be seen in the nostrils, but it is frequently swallowed and the only evidence of a problem is poor performance. Endoscope examination after exercise will show blood in the windpipe.
The most common treatment is a diuretic, furosemide (Lasix), which is denoted on the racing form when a horse has been administered this drug before racing.
In rare cases, blood-filled masses called ethmoid hematomas can grow at the back of the nasal passages. Intermittent nose bleeds from one or both nostrils with abnormal breathing sounds during exercise are the most commonly described clinical signs. Fatal bleeding is less of a concern with this disease.
Other common causes of nosebleeds in horses include clotting disorders, purpura hemorrhagica, which is blood vessel inflammation related to strangles infection, and equine infectious anemia, which is the disease tested for by a Coggins test.
Endoscopic examination with the horse sedated is the best option to differentiate these various causes of nosebleeds and determine the best treatment course.
Jamie Rothenburger is a veterinarian practising at Crossfield, Alta.