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Lecture – The Equine Hoof

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The Equine Hoof

EQS 110



Table of Contents

Functions of the Hoof .................................................................................................................................... 3

Basic Structure of the Hoof .......................................................................................................................... 3

Skeletal Components of the Hoof .............................................................................................................. 3

Sensitive and Insensitive Structures of the Hoof ...................................................................................... 4

Sensitive Structures .................................................................................................................................... 4

Insensitive Structures ................................................................................................................................ 4

Anatomy of the Hoof ...................................................................................................................................... 5

External Hoof Anatomy – Hoof Capsule .................................................................................................. 5

Hoof Wall ................................................................................................................................................... 5

Laminae .................................................................................................................................................. 6

Coronary Band ........................................................................................................................................... 6

Periople ....................................................................................................................................................... 6

External Hoof Anatomy – Solar/Ground Surface ................................................................................... 7

Sole............................................................................................................................................................... 7

Frog.............................................................................................................................................................. 7

Bars .............................................................................................................................................................. 8

Heel Bulbs .................................................................................................................................................. 8

Internal Hoof Anatomy ................................................................................................................................ 9

Digital Cushion .......................................................................................................................................... 9

Lateral Cartilages ........................................................................................................................................ 9

Blood Flow of the Hoof ............................................................................................................................... 10

Management of the Hoof – Thrush & Abscesses ............................................................................... 11

Thrush ........................................................................................................................................................... 11

Abscess .......................................................................................................................................................... 12

Diagrams of the External Hoof ................................................................................................................ 13

Glossary ............................................................................................................................................................ 14

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Functions of the Hoof

The equine hoof is a complex and strong structure that must

bear the weight of the horse and concussive forces during

exercise. There are five main functions of the hoof:

Provide a weight bearing surface

Protect the sensitive internal structures of the foot

Maintain moisture in the foot

Provide grip/traction

Act as a shock absorber

Basic Structure of the Hoof

In order to carry out the functions presented above, the hoof is comprised of both skeletal and

non-skeletal components. We will look at hoof structure and anatomy in great detail in order to

better understand its ability in facilitating locomotion and support.

Skeletal Components of the Hoof

There are three bones that are within the hoof capsule, starting most proximal to distal:

Distal end of the Middle Phalanx (P2/Short Pastern)

Distal Sesamoid (Navicular Bone)

Distal Phalanx (P3/Coffin Bone/Pedal Bone)

In order for locomotion (movement) to occur, these bones

are connected by joints, ligaments, and tendons, many of

which we discussed in the previous lecture on connective

structures:

Coffin Joint – synovial joint within the hoof capsule

Deep Digital Flexor Tendon (DDFT) – attaches to

the bottom of P3, allows the leg to bend or flex

One connective structure that we will add to this

discussion is the common digital extensor tendon. This

tendon attaches to the top/front of P3 and allows the leg

to straighten/extend.

Due to a hard cavity (hoof wall) surrounding these

components, issues with the hoof’s musculoskeletal

components can be difficult to treat.



Sensitive and Insensitive Structures of the Hoof

In addition to the skeletal components of the hoof, there are also sensitive and insensitive structures

within the hoof capsule that play a vital role in maintaining the main functions of the hoof.

Sensitive Structures

Sensitive structures lie underneath the hard, outer portion

of the hoof and contain many nerve and blood vessels. Also

referred to as corium, sensitive structures are named

according to the insensitive structure it underlies and

produces. For example, the frog corium (sensitive) lies

below and produces the insensitive frog, which is what we

visibly see when we clean out a horse’s hoof. Damage to

the sensitive structures of the foot can result in poor

development and growth of the corresponding structure.

Insensitive Structures

Insensitive structures are referred to as horny layer structures.

Insensitive structures of the hoof are those that are exposed (we

can see), such as the wall, bars, sole, frog, etc.

Frog Corium (Sensitive)

Note the visible blood vessels Insensitive Frog



Anatomy of the Hoof

We can categorize the various anatomical structures of

the hoof into two distinct categories:

External Anatomy

Internal Anatomy

External hoof anatomy consists of the hoof capsule and

the solar (bottom) surface; these are all the structures

that we can see and touch. Internal hoof anatomy

consists of those structures within the hard hoof capsule, many of which are elastic and help

absorb concussive forces.

External Hoof Anatomy – Hoof Capsule

Hoof Wall

The hoof wall is a multi-layered structure that functions to house and

protect the sensitive inner foot, support weight, resist wear, conduct

moisture and absorb shock. Externally, the hoof wall is divided into

three regions:

Toe

Quarters (Medial & Lateral)

Heel

A horse’s hoof wall is thickest at the toe and thins toward the heel.

The growth of the hoof wall begins at the coronary

band. A horse grows approximately 0.25 (1/4) inch

of hoof wall per month but this can vary; growth

tends to be slower in cold or dry environments.



Laminae

While the hoof wall looks like a relatively rigid,

inelastic structure, it actually has the ability to

expand around ¼ of an inch when contacting the

ground. Its ability to expand, absorb shock, and

support weight is due to laminae, which are “leaf-

like”, interlocking structures found on the

innermost layer of the hoof wall. Laminae are

responsible for attaching the hoof wall to the

coffin bone; this attachment is so strong that

laminae are able to sustain 2,000 pounds of force

landing on each forefoot during a running stride!

With the laminae junction absorbing up to 67% of

the impact force, they, unfortunately, weaken over time due to repetitive stress and/or disease.

This can result in inflammation, pain, and coffin bone instability, which are signs and symptoms

associated with laminitis.

Coronary Band

The coronary band is a rim of tough, vascular specialized skin

that is the primary source of growth and nutrition for the hoof

wall. It helps produce components of the outer hoof wall as

well as being a band of support to add strength to internal

structures. Damage to the coronary band can have a serious

negative effect on hoof growth and development, with severe

cases resulting in permanent disfigurement of the hoof.

Periople

The periople is found just below the

coronary band and it provides a protective

covering for newly formed hoof wall.



External Hoof Anatomy – Solar/Ground Surface

Sole

The sole is a thick plate of flaky horn that covers most the

solar surface, also called the ground (bottom) surface. Its

job is to protect the sensitive structures underneath it. A

common misconception about the sole is that it should

bear weight, but this is highly incorrect – the sole of the

horse is not designed to be constantly bearing weight from

the ground surface! If this occurs or if it hits a hard

structure (such as a rock) it can become bruised, resulting

in lameness.

When we discuss the sole we also have to mention a

structure called the white line. The white line is the

junction between the wall and the sole. The role of the

white line is to seal off the internal hoof from bacterial

infiltration. Improper care of the hoof can result in white

line disease, which weakens the white line, potentially

exposing it to bacteria.

Frog

The frog is a wide, thick, triangular-like structure that sits in the

middle of the hoof’s solar surface. It aids in protecting the sensitive

structures that sit underneath, providing traction, assisting in

circulation, and absorbing shock. On each side and in the middle of

the frog is a groove, called the collateral groove or collateral sulcus

(see above image). Special attention must be made to cleaning out

these grooves when picking the feet, as they can become invaded

with dirt, debris, and bacteria. An unhealthy frog is vulnerable to

infection that can result in severe lameness!



Bars

On the solar surface of the hoof, the bearing edge of the hoof wall is visible as well as the bars.

The bars are an extension of the hoof wall that adds strength to the heel area.

Heel Bulbs

A horse’s heel bulbs are located towards the back of the hoof and are similar to the fleshy part

of the palm of your hand. This particular structure is vulnerable to bruising as well as injury

since it is not protected by the hard hoof capsule.



Internal Hoof Anatomy

Digital Cushion

The digital cushion is the main shock absorber of

the hoof. It is located behind the coffin bone and

plays a vital role in the transfer of blood in the

foot. When the foot does not function properly or

is not exercising enough, the digital cushion can

atrophy, becoming “fatty” rather than “springy”,

which reduces its shock absorbing capability.

Lateral Cartilages

The lateral cartilages encapsulate the back of the coffin bone and act like a hammock to provide

resistance as the coffin bone descends when bearing weight. Competitive injury and repetitive

trauma can cause the lateral cartilages to ossify (change into bone), which can then restrict

their ability to support and reduce shock.

Video Clip – Good vs. Bad Digital Cushions

https://www.youtube.com/watch?v=o8K184QkJAU









Blood Flow of the Hoof

The strength of the hoof depends on nourishment from good

circulation and vascularity. The horse is a unique animal in

that there are no muscles in the lower leg or hoof to aid in

the return of venous blood back to the heart. Therefore, the

hoof and its structures have to assist in this mechanism.

Circulation of blood to and from the hoof is dependent on:

Activity

Hoof balance

Nutrition

Horses are designed to be in a constantly moving state, which promotes

good circulation. In situations where a horse is not able to freely roam

(such as the racehorse), we must incorporate activity via exercise, hand

walking, or turnout to assist blood flow to and from the hoof.

In addition to activity, the hoof must also be engaging its external solar

surface. A hoof that is balanced will appropriately engage its solar

surface whereas a hoof that is unbalanced (higher on one side then

another, too long in the toe, too high in the heel, etc.) will not.

Maintaining a routine schedule with your farrier for trims and shoeing

(if needed) will be key to keeping the hoof balanced. The surface that

your horse stands on will also impact his ability to engage the solar

surface; a footing that “cups” the hoof is ideal (such as shavings or

sawdust) while hard, concrete-like surfaces are not.

Lastly, the nutrition that your horse receives will have an overall effect

hoof health and thereby, circulation.

An Unbalanced Hoof



Management of the Hoof – Thrush & Abscesses Taken in part from Hoof Care for Racehorses” by T.A. Landers, April 30th, 2011

Everyone involved in the care and management of a horse has a role in maintaining appropriate

hoof health. Poor management of the hooves can lead to disease and lameness, which can

result in days lost in training and setbacks from racing, in addition to pain and discomfort felt by

the horse. Consistent, daily cleaning of the hooves, providing the horse with sanitary living

conditions, and routine farrier care are all vital to your horse’s hoof health. Unfortunately, not

all caretakers are diligent in these measures or there are hoof ailments that no matter how

persistent you are, still occur. With a foundation of hoof anatomy knowledge, we will look at

two of the most commonly seen hoof ailments – thrush and abscesses.

Thrush

Thrush is a bacterial infection affecting the frog

(particularly the collateral grooves/sulci) on one or

more feet. This issue is generally caused by general

neglect of the feet – allowing the horse to stand in

unsanitary conditions such as manure-filled and urine-

soaked stalls and paddocks. Extremely wet outdoor

living conditions and excessive frog growth due to

infrequent trimming may also contribute to thrush.

Diagnosing thrush is extremely clear from clinical signs

– the most obvious symptom is a foul odor, but other

symptoms include extensive moisture of the frog, heat, and a thick, black discharge from the

grooves. In severe cases, a horse may be lame and/or have a systemic bacterial infection.

Thrush is an easily curable ailment if treated as soon as it is diagnosed.

Depending on the severity, you may need your farrier to remove all dead frog

tissue, followed by washing the bottom of the foot thoroughly with warm

water and a mild disinfectant such as Betadine, and then applying a liquid

thrush remedy that will help clear out the bacteria. Less severe cases may call

for just a thorough cleaning of the foot, followed by application of a liquid

thrush remedy for 3-5 days or until the issue resolves. In addition to treating

the foot, make sure the horse is being kept on clean and dry bedding.

Preventing thrush comes from proper management: clean the horse’s feet

thoroughly (several times a day) and keep his living conditions sanitary,

whether it is in a stall or in a paddock. No competent horseperson allows a

horse in his or her care to develop a severe case of thrush!



Abscess

A hoof abscess is an infection in the soft tissues of the foot,

most commonly under the sole or hoof wall. Because the

soft tissues of the foot are encased in a rigid box (the hoof

wall and sole), the pus caused by an infection has no easy

avenue of escape. Pressure builds up, causing pain and

further disruption of the soft tissues. Because the pus tends

to move along the path of least resistance, most abscesses

break out at the coronary band.

Most abscesses start with a hoof crack or separation

(defect) of the wall and sole at the white line. This allows

dirt, mud, manure, tiny bits of gravel, and water to enter. As the horse puts weight on the foot,

this material packs deeper and deeper into the foot, causing disruption of the sensitive tissues.

Abscesses may also occur because of a bruise or wound to the sole.

Horses with a hoof abscess will often show sudden and

severe lameness, to the extent that they cannot put any

weight on the affected hoof. The hoof wall is often noticeably

hot to the touch over the abscessed area, and an increased

pulse in the arteries at the back of the fetlock is usually

evident. If you call out your farrier or veterinarian to examine

the horse, they may use a tool called hoof testers to squeeze

various areas of the hoof in order to identify sensitivity.

The most important part of treating an abscess is to identify

drainage. This is often accomplished by soaking the foot several

times daily in warm water and Epsom salts in order to encourage

the abscess to “pop” and drain. In severe cases, your veterinarian

or farrier may have to open up the sole or hoof wall to allow for

drainage. Once the abscess has started to drain, it is vital that the

area is kept clean and allowed to fully drain; abscesses can recur

if they do not heal properly the first time.



Diagrams of the External Hoof

Frog

Bars

Hoof Wall

White Line

Sole

Collateral Groove/Sulci

Sulci of the Frog

Heel Bulbs



Glossary

Abscess – An infection in the soft tissues of the foot characterized by hoof inflammation and lameness

Bars – Found on the solar surface of the hoof, an extension of the hoof wall to add strength to the heels

Coffin Joint – The only synovial joint found in the hoof capsule

Collateral Groove – A depression found on each side of the frog as well as in the middle of the frog

Common Digital Extensor Tendon – Found on the front of the limb, attaches to the top of P3

and allows the limb to extend/straighten

Corium – Refers to the sensitive structures of the foot that contain the many nerve and blood vessels

Coronary Band – A rim of tough, vascular specialized skin that is responsible for hoof growth and nutrition

Deep Digital Flexor Tendon (DDFT) – Found on the back of the limb, attaches to the bottom of

P3 and allows the limb to flex/bend

Digital Cushion – An internal elastic structure that is the main shock absorbed of the hoof

Frog – A thick, wide, triangular-like structure found on the solar surface of the hoof

Heel Bulbs – Found on the back of the hoof to aid in shock absorption, can be easily bruised or injured

Hoof Capsule – Hard covering that protects inner sensitive structures, comprised of the

coronary band, periople, hoof wall, and solar surface

Hoof Testers – A diagnostic tool used to check for hoof sensitivity

Hoof Wall – A multilayered structure that grows from the coronary band

Horned Layer – Refers to insensitive structures of the foot

Laminae – Leaf-like interlocking structures that help attach the hoof wall to the coffin bone

Laminitis – Inflammation of the laminae

Lateral Cartilage – An internal elastic structure that provides resistance to the coffin bone when

taking weight

Periople – Found below the coronary band, provides a protective covering for new hoof wall

Solar Surface – The ground or bottom surface of the hoof

Sole – A thick plate of flaky horn that covers most of the solar surface to protect internal

sensitive structures

Thrush – A bacterial infection of the foot that is often the result of general neglect of the feet



Trim – A practice performed by a farrier to remove excess hoof wall, frog, etc., should occur

routinely in order to maintain hoof balance

White Line – The junction between the wall and sole, seals off the sensitive structures of the

hoof from bacterial infiltration

White Line Disease – An ailment that results in the weakening of the white, often the result of

improper care of the hoof

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