Mystery and old wives’ tales surround the chestnut, the odd little growth on the inside of most horses’ legs.

chestnut ergot on hind leg
The chestnut, the oily, scaly callosity on the inside of some horses’ legs, is thought to be a vestigial toe from the prehistoric genus ‘Eohippus.’

The horse is truly a creature of mystery. If I ever had the chance, there are so many questions I would like to ask him.

Why do you carry us humans upon your back? What do you think about while standing around at odd hours of the night? Why must you stomp your feet at such inopportune times? And why exactly do you have chestnuts on your legs?

The chestnut has always baffled me. Now, let’s be clear, by chestnut I mean the callosity that always grows on the inside of the equine foreleg and below the hock on the hind leg as well. Some refer to them as “night eyes.” I noticed the chestnut for the first time when I was about 8, and thought that my horse had some sort of a strange growth or fungus. I fretted over what to do, even lost a little sleep over the deal. However, I finally deduced that each and every horse had the same thing as mine and I was able to rest peacefully, reasoning that they are perfectly normal.

And that’s the strange thing about a chestnut –  it is a perfectly normal part of the equine anatomy. It’s been theorized that the chestnut is a small reminder of either the horse’s long lost toe or a scent gland that has been lost via evolution from the equine ancestor Eohippus. To me, that theory sounds a little bit far-fetched and scientific, but since there is no other real explanation, it is perhaps the best explanation as to why our horses still have them. Strangely enough, zebras and donkeys do not have chestnuts on their hind legs.

Speaking of strange, there’s another little growth that occurs on many horses called the ergot. It too, is a callous type of growth that reminds me a bit of an eraser on a mechanical pencil. If present, ergots are found on the bulb of the fetlock of a horse, often undetectable as they are covered by hair. Some horses have them on all four legs, and others don’t have ergots at all.

Chestnuts are unique to each and every horse, much like a human fingerprint. Sometimes they stay smooth throughout a horse’s life, some have a rough and jagged surface, and others will grow and stack up and thicken over time. I’ve heard a theory that if you peel a chestnut off and then carry the peelings out to a pasture of other horses, they will come up to investigate it and therefore be easy to catch. Hmmm. Can’t say I’ve tried it.

After doing some research on this topic, I realize that there are only two types of people in life: those who leave a horse’s chestnuts and ergots alone, and those who cannot. I happen to be one of the latter. If, like me, the appearance of an overgrown chestnut irks you, the best thing to do is to soften it up with a bath or some sort of Vaseline or baby oil, and peel it with your fingers or trim it back with some sort of a safe tool. Naturally, you don’t want to take them down any deeper than skin level and always stop if the horse seems uncomfortable during the trimming attempt.

And as if they couldn’t get any more mysterious, I must say, the weirdest part about these funny little growths is the smell. Horses’ chestnuts have a pleasant, smoky, horsey odor to them. I actually kind of like it.

If you ever get the chance, have a little sniff yourself— though I recommend you do so only once they’ve been trimmed off of the animal’s leg.

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