Horse hoof

A horse hoof is the special part at the end of each leg of a horse. It touches the ground and helps the horse carry its weight. The hoof is both hard and bendy, which makes it very useful.

The hoof surrounds the end of a small bone called the distal phalanx of the 3rd digit. This is part of the basic pentadactyl limb found in many vertebrates, which in horses has changed over time to just one main digit that helps with weight-bearing. The hoof is covered with soft tissue and a tough material called keratinised matter, which helps protect it.

Anatomy

The hoof of a horse has two main parts. The outer part, called the hoof capsule, is made of tough, hardened material. The inner part is made of soft tissues and bone.

The hoof capsule protects important structures inside, like tendons and ligaments. The top edge of the hoof capsule is called the coronet. The walls of the hoof start from the coronet and are longest at the front (toe), medium in length on the sides (quarter), and shortest at the back (heel). Between the heels is a flexible area called the frog. The bottom of the hoof is covered with a special material called the sole.

Characters and functions of the external hoof structures

The walls

The walls of a horse's hoof act like a shield, protecting the sensitive tissues inside. They are tough and stretchy, and they help the horse grip different kinds of ground. The walls are made of three layers: a colored layer, a water layer, and a white layer. These layers grow together and help keep the hoof strong. If the walls don’t wear down naturally, they can stick out and might break off to stay healthy.

When a horseshoe is put on, it attaches to the wall using special nails that go into the wall at a slant.

The wall is similar to human fingernails or toenails.

The frog

The frog is a V-shaped part on the underside of the hoof. It helps absorb shocks and gives grip on hard ground. It also helps move blood back to the heart. In horses that stay in stables, the frog can become soft and damaged, but in horses that roam freely, it hardens and stays strong. If a horse’s frog gets too wet, it can get an infection.

The frog is similar to human fingertips.

The sole

The sole is the bottom part of the hoof. Its color can be whitish-yellow or grayish. It can be soft if it doesn’t touch the ground much, or very hard if it’s always on the ground. If a horse steps on a sharp object, it can hurt the sole and make the horse limp.

The bars

Bars are folds in the wall that start from the heels. They help keep the hoof strong. If they grow too long, they can cover part of the sole.

Internal structures

The bone inside the hoof, called the coffin bone, is shaped like a crescent wrench and is almost completely covered by the hoof. There is a soft layer between the bone and the hoof that helps keep it strong. Under the back part of the sole, there is a cushion that protects the frog and other parts from injury. In young horses, this cushion is soft, but in adults, it becomes tougher to support the hoof.

The hoof mechanism

The horse hoof is not stiff like a rock. It is flexible and can change shape. When a horse puts weight on its hoof, the hoof flattens a little. This happens because of the curved shape of the hoof. When the hoof is not carrying weight, it only touches the ground at the front and back parts. But when the horse steps down, more of the hoof touches the ground.

When the hoof carries weight, it changes in several ways. The bottom part flattens, the front part spreads out a bit, and the hoof gets a little bigger. This helps the blood flow well in the hoof. When the hoof is lifted, it goes back to its smaller shape, helping to push the blood out. This movement helps keep the blood circulating in the hoof.

Time-related changes of the hoof

Hooves change over time in two ways: in the short term (days or weeks) and over the horse's whole life.

In the short term, a horse's hoof grows from its skin. Special cells in the skin make tough material that forms the hoof. This material hardens and moves downward, helping to protect the horse's foot. In the wild, a horse's hoof wears down naturally by walking on the ground. But for horses that live with humans, people need to help by trimming and caring for the hoof.

Over a horse's lifetime, its hooves change shape based on how the horse moves and any health conditions. This shows how hooves can adapt. Wild horses, like Mustangs, show this adaptability well, staying healthy in many different places.

Hoof evolution

Horse hooves developed over 55 million years through evolution of the horse. Long ago, the ancestor of horses, called Eohippus, had four toes on its back feet and three on its front feet. Today, all wild and domestic Equus animals have hooves that look and work in much the same way. Over time, horses lost some of their toes, which helped them run fast and move easily on hard, flat lands like prairies and deserts (this is called cursorial specialisation).

In 2018, scientists discovered that a horse’s hoof might still hold tiny pieces of the toes it once had.

Disorders

Horses can get several health problems in their hooves. Two of the worst are laminitis and navicular disease. Other common issues include thrush and white line disease, which are bacterial infections that need treatment. Quittor is an infection that affects the lower leg and is more common in draft horses. There is also a genetic disease called hoof wall separation disease.

Another issue is quarter cracks, which are vertical splits in the hoof wall. These are often found on the inside of front hooves or the outside of hind hooves. They can happen due to poor shoeing, how the hoof is shaped naturally, or from injuries to the leg and hoof.