Horse hooves are amazing structures that allow horses to run, jump, and carry heavy loads. They are also very complex and require proper care and maintenance to keep them healthy and functional. In this article, we will explore the anatomy of horse hooves and learn about their different parts and functions.
The Hoof Capsule
The hoof capsule is the outer part of the hoof that is visible to the eye. It is composed of various cornified (hardened) structures that protect the inner, living part of the hoof from injury and infection. The hoof capsule consists of four main components: the wall, the sole, the frog, and the bars.
The Wall
The wall is the most prominent part of the hoof capsule. It is the curved structure that covers the front and sides of the hoof. The wall is divided into three regions: the toe, the quarters, and the heels. The toe is the front part of the wall that bears most of the weight of the horse. The quarters are the sides of the wall that help to stabilize the hoof. The heels are the back part of the wall that support the frog and absorb shock.
The wall is made up of two layers: the inner wall and the outer wall. The inner wall is white and more pliable than the outer wall. It has a higher moisture content and can stretch more as the outer wall moves. The inner wall also contains laminae, which are thin, interlocking structures that attach the wall to the underlying bone. The outer wall is pigmented and stronger than the inner wall. It has a lower moisture content and is almost impermeable to water and other substances. The outer wall also acts as a spring, storing and releasing energy during movement.
The wall grows continuously from the coronary band, which is a ring of soft tissue at the top of the hoof. The growth rate of the wall depends on various factors, such as nutrition, genetics, season, and activity level. The average growth rate is about 6 to 10 mm per month1. The wall needs to be trimmed regularly to prevent overgrowth, cracking, or splitting.
The Sole
The sole is the concave structure that covers the bottom of the hoof. It is located inside the white line, which is a yellowish band that joins the sole to the inner wall. The sole has three parts: the body, the apex, and the crus. The body is the main part of the sole that covers most of the area. The apex is the pointed part of the sole that corresponds to the toe of the wall. The crus is the curved part of the sole that corresponds to the quarters of the wall.
The sole protects the sensitive structures beneath it from pressure and injury. It also provides some support to the weight of the horse, especially around the toe area. The sole is made up of cornified material that is softer and thinner than the wall2. The sole sheds periodically as new material grows from the corium, which is a layer of vascular tissue under the sole.
The Frog
The frog is a triangular structure that occupies the central part of the hoof. It has three parts: the apex, the central sulcus, and the collateral sulci. The apex is the pointed part of the frog that faces the toe. The central sulcus is the deep groove that runs along the middle of the frog. The collateral sulci are the shallow grooves that run along the sides of the frog.
The frog acts as a shock absorber and a traction device for the hoof3. It compresses and expands with each step, cushioning the impact and enhancing the grip. The frog also helps to pump blood back to the heart by squeezing the digital cushion, which is a pad of fibroelastic tissue under the frog4. The frog is made up of cornified material that is softer and more flexible than the sole or the wall. The frog also sheds periodically as new material grows from the corium.
The Bars
The bars are extensions of the wall that run along the sides of the frog. They terminate approximately half way along the frog. Their primary purpose is to control the movement of the back of the hoof, adding strength to the heel area and protecting it from excess distortion5. They also help to support the weight of the horse, especially when the heels are contracted or underdeveloped. The bars are made up of cornified material that is similar to the wall. They grow from the coronary band and need to be trimmed regularly to prevent overgrowth or impingement.
The Inner Hoof
The inner hoof is the living part of the hoof that is hidden by the hoof capsule. It is composed of various soft tissues and bone that provide blood supply, sensation, and attachment to the hoof capsule. The inner hoof consists of four main components: the corium, the laminae, the digital cushion, and the coffin bone.
The Corium
The corium is a layer of vascular tissue that covers the inner surface of the hoof capsule and the coffin bone. It provides blood supply and nourishment to the hoof capsule and the coffin bone. It also produces the cornified material that forms the hoof capsule. The corium has five regions: the perioplic corium, the coronary corium, the laminar corium, the sole corium, and the frog corium.
The Perioplic Corium
The perioplic corium is a narrow band of tissue that surrounds the coronary band. It produces the periople, which is a thin layer of horn that covers the outer surface of the wall. The periople protects the wall from drying out and cracking.
The Coronary Corium
The coronary corium is a thick band of tissue that lies under the coronary band. It produces the wall, which grows downward from the coronary band. The coronary corium also contains papillae, which are small projections that interlock with the laminae of the wall.
The Laminar Corium
The laminar corium is a thin layer of tissue that covers the coffin bone and the inner wall. It produces the laminae, which are thin, interlocking structures that attach the wall to the coffin bone. The laminae have two types: dermal laminae and epidermal laminae. The dermal laminae are produced by the laminar corium and contain blood vessels and nerves. The epidermal laminae are produced by the inner wall and contain no blood vessels or nerves. The dermal and epidermal laminae fit together like velcro, forming a strong bond between the wall and the coffin bone.
The Sole Corium
The sole corium is a layer of tissue that covers the sole area of the coffin bone. It produces the sole, which grows outward from the sole corium. The sole corium also contains papillae, which are small projections that interlock with the laminae of the sole.
The Frog Corium
The frog corium is a layer of tissue that covers the frog area of the coffin bone. It produces the frog, which grows outward from the frog corium. The frog corium also contains papillae, which are small projections that interlock with the laminae of the frog.
The Laminae
The laminae are thin, interlocking structures that attach the hoof capsule to the coffin bone. They have two types: dermal laminae and epidermal laminae. The dermal laminae are produced by the corium and contain blood vessels and nerves. The epidermal laminae are produced by the hoof capsule and contain no blood vessels or nerves. The dermal and epidermal laminae fit together like velcro, forming a strong bond between the hoof capsule and the coffin bone.
There are two types of laminae: primary laminae and secondary laminae. The primary laminae are long and leaf-like structures that run parallel to the wall. They have about 600 in number per hoof. The secondary laminae are short and finger-like structures that branch off from the primary laminae. They have about 100 to 150 per primary lamina. The secondary laminae increase the surface area for attachment between the hoof capsule and the coffin bone.
The laminae are responsible for transmitting the weight of the horse from the coffin bone to the hoof capsule. They also allow for some movement between the hoof capsule and the coffin bone during locomotion. However, if the laminae are damaged or inflamed, they can lose their attachment and cause the hoof capsule to separate from the coffin bone. This condition is known as laminitis or founder, and it can be very painful and debilitating for the horse.
The Digital Cushion
The digital cushion is a pad of fibroelastic tissue that lies under the frog and behind the coffin bone. It acts as a shock absorber and a blood pump for the hoof4. It compresses and expands with each step, cushioning the impact and squeezing blood back to the heart through the veins in the hoof. The digital cushion also helps to stabilize the coffin bone
and support the back of the hoof. The digital cushion varies in size and shape depending on the breed, age, and activity level of the horse. Generally, the digital cushion is larger and firmer in horses that have healthy hooves and live in natural environments. The digital cushion can also be improved by proper hoof care and exercise.
The Coffin Bone
The coffin bone is the main bone of the hoof. It is also known as the distal phalanx, the third phalanx, or the pedal bone. It is shaped like a cone, with a wider base at the top and a narrower tip at the bottom. The coffin bone has three surfaces: the dorsal surface, the solar surface, and the parietal surface.
The Dorsal Surface
The dorsal surface is the front surface of the coffin bone that faces the toe. It is covered by the laminar corium and attached to the wall by the laminae. The dorsal surface has a convex shape that matches the curvature of the wall.
The Solar Surface
The solar surface is the bottom surface of the coffin bone that faces the ground. It is covered by the sole corium and attached to the sole by the laminae. The solar surface has a concave shape that matches the concavity of the sole.
The Parietal Surface
The parietal surface is the side surface of the coffin bone that faces the quarters. It is covered by the laminar corium and attached to the wall by the laminae. The parietal surface has a flat shape that matches the flatness of the wall.
The coffin bone provides support and structure to the hoof. It also houses the distal interphalangeal joint, which is the joint between the coffin bone and the short pastern bone (the second phalanx). The distal interphalangeal joint allows for some flexion and extension of the hoof during locomotion.
The coffin bone is also connected to the navicular bone, which is a small, sesamoid bone that lies behind the coffin bone. The navicular bone acts as a pulley for the deep digital flexor tendon, which is a tendon that runs along the back of the leg and attaches to the bottom of the coffin bone. The deep digital flexor tendon helps to flex the hoof and stabilize the distal interphalangeal joint.
The coffin bone can be affected by various diseases or injuries that can compromise its integrity and function. Some of these are:
- Osteitis: inflammation of the bone due to infection or trauma.
- Osteomyelitis: infection of the bone due to bacteria or fungi.
- Osteoarthritis: degeneration of the cartilage and bone due to wear and tear or injury.
- Fracture: breakage of the bone due to excessive force or stress.
- Navicular syndrome: inflammation or degeneration of the navicular bone or its surrounding structures due to chronic stress or injury.
Conclusion
Horse hooves are complex and fascinating structures that enable horses to perform various activities and tasks. They are composed of various parts that have different functions and characteristics. Understanding the anatomy of horse hooves can help horse owners to provide better care and maintenance for their horses’ hooves, as well as to prevent or treat common hoof problems and diseases.