Horses have a crusty remnant of evolution stuck to their legs

Horse Chestnuts

• Written by RACHAEL FUNNELL, IFL Science

EVOLUTION has a funny way of leaving the residue of past adaptations in strange places on animals’ bodies, and chestnuts on horses’ legs are a fine example. Nobody’s quite sure what horse chestnuts exactly are, but they’re believed to be a remnant left behind from horses’ five-toed ancestors.

For a long time, it was believed that modern horses had one toe on each foot, having evolved down from five digits. However, 2018 research argued that the digit reduction had been overstated, and that actually all five digits remain partially present in the forelimbs of modern adult horses.

Whether you like your horses five-toed or one is your business, but we’re on a mission to make you painfully aware of the crusty nodule that sits a little further up horses’ legs. Say hello to the horse chestnut.

Horse “chestnut”. Image by John Daniels. Fine Art America.

To the uninitiated, horse chestnuts look like crusty brown growths that can develop on the front and back legs of a horse. They can start off small and grow bigger in size, and eventually peel off without much resistance.

You might think it sort of sounds like a misplaced nail (which, by the way, a lot of seals have), but there are a few ideas as to what horse chestnuts once were. One idea is that they’re the vestigial remains of a scent gland that’s found in similar animals like deer. “Vestigial” is the name given to features that were once prominent but have fallen out of use in the course of evolution, like the human tailbone.

The good news is that while they may look a bit grim, horse chestnuts growing on legs aren’t a concern beyond cosmetics. They are benign growths that tend to fall off on their own. They are sometimes helped along by horse owners who may ease their removal with the application of oil [.]

Horse chestnuts tend to sit above the knees and, depending on the horse variety, may be present on all four legs or just the front ones.

Read complete article »

Featured Image: Horse Breeds, University of Maryland Extension »

Rachael Funnell is a fascinating writer. Read her other works at IFL Science »

NOTE: This is our final post for 2022 unless something major occurs over the next few days. See you again here in 2023. Thank you for being with us, taking part and caring about horses. You are all stars. — THE FUND FOR HORSES.

Tuesday’s Horse

Official Blog of The Fund for Horses

2 thoughts on “Horses have a crusty remnant of evolution stuck to their legs”

  1. I remember the first time I saw one come off. I called the Vet who kindly and patiently explained what it was, and he need not come out. It still seems odd to me. -Vivian, Editor of TH.


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