A lot of people have probably noticed thoroughbreds coming off the track at the end of a race with blood dripping out of their nose. Maybe we have even seen this in our own equine pals after an intense workout. We all get nosebleeds sometimes, right? No problem. Stick a tissue up there and call it good. Unfortunately, that’s not the case for horses. Nose bleeding is more often than not an indication of a problem brewing.
Going back to the human nosebleed, it's important to note we have many large veins under our skin inside our nose. Sometimes, when the epidermis layer gets dry and cracks, we bleed out our nose through that surface level skin layer, which you all know, is typically not a big deal.
However, the blood in the tired horse’s nose did not come from that skin layer within the nasal cavity – it came from the lungs. For those of you who aren’t all too familiar with the layout of a lung, the “big tube” that brings the breath of air down from your mouth to the lungs (the trachea) breaks into two smaller tubes (the bronchi) that each enter into the right and left lung lobes. Those continue to split, and split, and split until they resemble a sort of tree formation. At the very ends of these branches, there are small round sacs called alveoli, which look like grapes on a vine. Here’s the cool part: how does the oxygen sitting in the alveoli, brought in through the mouth, make it to the bloodstream to feed the tissues of the body? There are capillaries (which are tiny blood vessels) right along the alveoli, virtually attached to the outside of these little sac-like structures. How does the gas go from the sac to the bloodstream? It diffuses through the lining. It’s a tad more complicated than this, but we will keep it simple for now for the sake of understanding the problem here. When a horse gets going too hard, that tissue layer pulls and pulls and blood enters the alveoli (sacs) and comes up the respiratory tract and out the nostrils.
The moment you see blood is not necessarily time to panic, but if it happens repeatedly, it becomes a concern for athletic horses. Remember that lining where the gas (oxygen) exchange happens that I was talking about earlier? If it is torn multiple times, it will harden, much like how any other damaged tissue repairs itself. Once that lining is hardened, oxygen exchange becomes much less efficient, and the horse is unable to perform as it used to. In extreme cases, this can cause a horse to become hypoxic (lacking oxygen) and pass out upon heavy exercise.
There are currently two ways to prevent this in the equine world. Jockeys may use a nasal strip (yes, I am serious) to open the airways and decrease resistance. If you have ever had a cold and used one of those nose strips, it looks very similar to this. A second is a drug called Furosemide, which causes the horse to eliminate more, which lowers fluid in the body, and therefore drops the blood pressure, bringing less stress to the capillaries in the lungs. I’ll save you more of that physiological intimidation – diuretic drugs are a whole other post!
Anyways, just a quick explanation for those of you who have ever seen, and wondered, where post-exercise horse nosebleeds come from (besides an injury or trauma). Cheers!
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