Mystery Solved: Guttural Pouches

We know that all horses have a guttural pouch, and some of their distant relations have a smaller version of the same structure. But until very recently, we didn’t know why they existed.

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What an amazing athletic machine is the horse. Few other animals of similar size and bulk manage to move with such efficiency, grace, and sheer speed. But despite our having worked side by side for centuries, there’s still much we don’t understand about a horse’s inner workings.

Take the guttural pouch, for example. It’s a strange, fist-sized cavity high up in the horse’s skull, slightly behind his ears. Officially, it’s an “outpouching” of the eustachian tubes (the passageway that takes in soundwaves from the ears), which drains just behind the nasal septum. Technically speaking, there are two guttural pouches, separated by a thin membrane–one for each eustachian tube–but for the most part they’re referred to as a single structure. All the guttural pouch seems to hold is air–about 300 to 500 ml worth on each side.

We know that all horses have a guttural pouch, and some of their distant relations have a smaller version of the same structure (rhinos, tapirs, and hyraxes–those little short-eared mountain rabbits). We know that very few other animals have anything similar. But until very recently, we didn’t know why they existed.

Various fanciful functions for this big air space have been proposed over the centuries–a resonating chamber for the equine whinny, perhaps? A mechanism to help horses swallow? An air pressure regulator for the ear drum? A hearing aid? But basically, it seemed the guttural pouch’s raison d’etre was to be the equivalent of the human appendix–an apocryphal structure whose main function was to cause trouble. As anyone who has struggled with respiratory disease in his barn knows, the guttural pouch is a prime site for stubborn infections, either bacterial or fungal, which can cause persistent drainage of gunk from one or both nostrils. On occasion, the guttural pouch can suffer from a condition called tympany, in which it overinflates with air. (This happens most often with foals, who end up looking like chipmunks storing nuts for the winter.) It’s also prone to hemorrhages from the internal carotid artery, which runs for about 10 cm through the thin mucous membrane of the guttural pouch on its way to the brain

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Written by:

Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She’s written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.

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