Equids, members of the horse family including horses, donkeys and zebras, share curious features called chestnuts. Found on every horse, they appear as toughened growths on their limbs, and can be clipped back if they grow too large. Anyone following the charming and rugged farrier Sam Wolfenden on TikTok will have seen his expert chestnut clipping.

Chestnuts are fascinating little entities – remnants of toe pads that were present in the prehistoric relatives of both domestic and wild horses. They’re also unique to each animal; you can think of them as an individual fingerprint.

Chestnuts are made of keratin, the same material found in the outer layer of skin. It’s protective, waterproof and durable, giving resilience and strength. It’s also found in hair and nails, which allow for important functions like trapping heat and providing sensory information to the brain.

The hooves and horns of animals are no different. Keratin-based and developed from the skin, they are designed for functions such as protection or even as weapons in battle.

Keratin therefore plays an important role across both human and animal species. And since we’re all built from similar biological materials, it may not surprise you that humans can develop horns too – though not quite like a horse or........

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