Structures of the Equine Foot

Bulbs of the heel--These structures are at the back part of the ground surface of the foot, behind the angle of the hoof wall. Internally, they receive support from the digital palmar (front feet) or plantar (hind feet) cushion.

Frog--This is a triangular or wedge-shaped structure with the apex pointing toward the front or toe of the hoof. Two grooves, one on each side of this structure, are known as the collateral or frog sulci. The central ridge is named the frog stay or spine of the frog and contains a furrow called the central sulcus or the cleft.

Bars--Near the heel, the wall of the hoof turns back toward the front portion. This continuation forms a ridge bordering the collateral sulci on both sides of the frog; these ridges are known as the bars.

Wall--This structure surrounds the foot and all inner parts. It is tough, fibrous, and somewhat elastic in nature and continually grows downward from the coronet. It is divided into three general areas--toe, quarter, and heel.

Sole--The sole makes up a major portion of the surface area of the bottom of the hoof, but it is not designed to be the animal's primary weight-bearing structure. It provides support for the inner structures.

White line--This boundary serves as a junction between the wall and the sole and is clearly visible around the front three-fourths of the circumference of the sole in a freshly trimmed foot.

Third phalanx (3P)--It is also called the distal phalanx, os pedis, pedal bone, and coffin bone. It is the most distal (farthest out from the body) of the four bones comprising the digit (equivalent to man's finger or toe) and is completely enclosed by the hoof. Interaction between this bone and the surrounding hoof structures serves as a shock absorber for the horse in motion.

Second phalanx (P2)--This bone is also called the middle phalanx, os phalanx, and the short pastern bone. It rests on the third phalanx and articulates with it and the first phalanx, which is above P2.

Distal sesamoid--This structure is often called the navicular bone or shuttle bone and is located on the back surface of both the second and third phalanx. It is an integral part of the shock absorbing mechanism, along with its ligamentous attachments.

First phalanx (P1)--This bone is also called the os compendale, os saffragenous, and long pastern bone. The first phalanx is the longest bone of the digit. It rests on the second phalanx and also articulates with the third metacarpal (in the foreleg) or metatarsal (in the hind leg), also called the cannon bone. It is closely attached to the paired proximal sesamoids by strong ligaments.
Johnson and Asquith then provide nomenclature for other structures within the foot.

Corium or pododerm--This part of the foot, they say, can be divided into five parts, but for discussion purposes, they considered only the general term and its function as a nutritional source to the hoof. Within this structure lies a massive supply of blood vessels that feed the hoof. These blood vessels--combined with nerves--form a sensitive layer intimately attached to the inside of the hoof wall and the third phalanx.

Digital (palmar or plantar) cushion--This is a wedge-shaped, modified subcutaneous tissue located within the back part of the hoof and composed of elastic fibers and some cartilage. As the name implies, it reduces concussion to the foot and puts pressure on blood vessels with weight bearing, which helps pump blood out of the foot.

Tendon of the common digital extensor muscle--It is considered in this discussion, the authors say, because of its insertion onto a process (protrusion) of the third phalanx and on the anterior (front) surfaces of the second and third phalanges. Its action is to extend the digit.

Deep flexor tendon--This is an extension of the muscle lying on the back part of the leg and which inserts on the posterior aspect of the third phalanx. It flexes the digit.

Superficial flexor tendon--This structure runs parallel to the deep flexor tendon and splits below the fetlock to insert on both the first and second phalanges. It also flexes the digit, but not the coffin joint (between P2 and P3).

Contracted Heels in the Horse

--A contracted foot is one where the foot is more narrow than normal, especially in the heels. It is most common in the front feet, and is most often bilateral, but it can be in only a single foot. Donkeys and mules have a narrower foot that in a horse would be called contracted. Tennessee Walking Horses and American Saddlebreds may have contracted heels when placed in show plates, as the hoof wall is excessively long and there is no frog pressure. Contracted heel (or foot) often occurs from an improperly trimmed and shod hoof. These horses may have imbalance (medial-lateral and/or cranio-palmar) long toes, or under-run heels. It should be noted that bar shoes do not prevent the foot from expanding, especially if the nails are set forward. Lame horses may develop foot contraction; those with fractures, septic conditions, severe tendon problems, or when the foot is placed in a cast for a prolonged period. Dry feet cannot expand normally and may contract, as do feet with a long toe-short heel trim. Foot contraction can also be due to the use of a shoe that is too small. The foot is then fit to the shoe instead of the other way around. The foot will eventually grow to small shoe and contract. A contracted foot often has an increase in concavity of the sole, so that the frog does not reach the ground. The contraction may cause the horse to be “hoof-bound”, where the heels may contract around the navicular bone or coffin bone (distal phalanx), pressing firmly against the bone. In severe cases, the bars may contact each other. All of this results in destruction of the digital cushion, resulting in a weak foot with no internal support. In the chronically contracted foot, there may be loss of the circular shape of the foot. The digital cushion atrophies and becomes less resilient and fails to protect the deep flexor tendon and navicular bone, potentially leading to navicular disease. The atrophied frog may contain thrush, and the wall, sole, and frog may become hard and dry. Heel contraction occurs in feet with a full, soft frog. Thus, the contraction results from the foot conformation, lameness, or an abnormal environment. Management of contracted heels can take prolonged periods of time to correct if it can be at all. Any lameness issue should be diagnosed and corrected. The horse should be put in an appropriate shoe size and the nails should be kept forward of the bend in the quarter. It is not wholly necessary for the frog to contact the ground for heel expansion and blood flow; in fact, it is contraindicated in this type of foot as lowering the heel too much will cause other problems due to breaking the hoof-pastern axis even further. Over time, the frog may become more normal, with gradual changes to the hoof conformation. If the foot is trimmed properly, the foot will expand during weight bearing, allowing blood into the foot, and the hoof capsule will contract when the foot is removed from weight bearing. In most horses, balancing the foot and correcting the hoof axis is the first part of correction. The shoe can be set slightly wide at the heels and quarters and longer at the heels. Again, the last nail should be at the bend in the quarter. In horses with long toe-short heel, emphasis is placed upon shortening the toe, leaving the heel alone whenever possible. The heel should be supported with a bar shoe .Other methods of increasing heel expansion include thinning the quarters or placing a groove in them, parallel to the coronet. These are used for severe contraction of the heels.

The Equine Frog

-- The frog is a central structure on the bottom of the equine foot.  It serves a variety of functions to help keep a horse sound.  When the hoof has issues, the frog deteriorates and the problem is self-exacerbating, leaving the unhealthy frog prone to thrush and possibly canker, both bacterial and/or fungal diseases of the frog and surrounding tissues.  The frog is involved in shock absorption, blood flow, protection, coordination, and traction for the equine foot. The frog is a wedge-shaped rubbery tissue between the bars of the sole.  It should be wide and substantial, and while keratinized, the frog is about 50% water, making the frog soft.  The apex points forward and the base, at the heel, has a shallow central sulcus.  A healthy frog in the unshod horse should have full contact with the ground surface.  It loads with each step.  A contracted foot with a recessed frog that never reaches the ground is unhealthy. A big robust frog that hits the ground and has as much contact as the hoof wall and the bars (the folds of the wall on either side of the frog) is working as it was meant.  The bars, frog, and caudal two-thirds of the hoof wall should contact the ground in the unshod horse. Shod horses, especially those with caulks, do not have contact with the ground.  Club feet have a recessed frog, and even some barefoot horses have a more concave foot than others. It acts as a shock absorber from the ground and redirects force from the bony column through the lateral cartilages of the hoof. The frog also pumps blood through the foot every time the hoof lands on the ground.  Below the carpus and tarsus, blood is pumped back toward the heart via venous plexus just above the frog.  An unhealthy frog can cause significant loss of structure in the caudal portion of the internal hoof, leading to lameness.  Horses with an unhealthy frog are more likely to stock up.  A healthy frog makes the limbs healthier and affects the whole body. The frog works with the coronet, bars, and sole to provide resistance to distortion of the hoof capsule.  Frog pressure influences the digital cushion above.  The frog stay (triangular area cut out of the sole that in which the frog sits) allows independent movement at the heels as the horse lands on uneven ground. The frog also plays a part in protecting the sensitive structures beneath, providing traction, assisting circulation, and absorbing shock.  In the center of the frog, towards the caudal aspect is the central sulcus.  A healthy sulcus is wide and shallow, but if the frog is weak and narrow it can become a deep crease which is a haven for bacteria and fungus.  This deep crease is common, but abnormal. The collateral groove (sulcus) runs along either side of the frog.  The outer wall of the groove is made up of the wall of the bar and sole and the wall on the other side comprises the wall of the frog. The horse’s heel has many sensory nerve endings, and the frog plays a role in proprioception (an awareness of where the feet and body are in space and time).  It may affect the foot fall on various terrains.  Its many nerves enable the horse to feel what it is standing upon. The frog also provides traction on various surfaces.  This is most noted in snowy and icy conditions, when barefoot horses seem to have better purchase (because the frog is in direct contact with the ground) than shod horses—unless the horse is shod with special traction devices.  The frog will stick to slippery surfaces and dig into soft surfaces.  It may help to stabilize the foot during weight bearing; along with the bars, the frog may seal the caudal edge of the concave sole so that it will act as a suction cup, sucking the hoof to the ground surface. Most of the time, the frog requires little trimming.  It should be trimmed to match the dermal frog (the solid base from which it grows).  Loose edges should be removed, and enough frog to help prevent thrush from pockets where bacteria may flourish.  The frog also exfoliates, or sheds, once of twice each year, which can be perceived as the frog is “falling off”.  It is simply shedding the old dead tissue.  There is a natural separation between the old frog and the new tissue underneath.  This can be removed before it traps mud and debris, leading to thrush.  Daily hoof picking is advised to clean the collateral sulci, which also helps to prevent thrush. Fissures may form in the central sulcus of the frog, most likely due to shearing forces that move the heels in opposite directions.  This condition is seen in horses with hoof capsule distortion, and compromised frog tissue.  Such fissures may extend into the skin above the heel bulbs, causing hemorrhage and lameness. Fissure formation in the central sulcus begins when the frog loses functionality, usually because the frog is not in ground contact, causing atrophy.  This may occur in horses with low heels, sheared heels, club foot, low heels, or inappropriate farriery.  An atrophied frog can no longer self-clean, and debris more easily accumulates, creating pressure, further exacerbating deterioration of the frog.  Weakened by the reduced protective horn of the epidermis, the frog tissue Wikipedia becomes susceptible to penetration by bacteria and other organisms leading to the development of the thrush.  The frog / digital cushion complex forms the bulk of the palmar foot and forms the connection between the heels of the hoof capsule.  This causes an asymmetrical loading pattern at the heel bulbs causes shearing forces and a fissure at the caudal frog and heel bulbs. In the case of low heel conformation, the heels move dorsally, and the soft tissue structures (frog and digital cushinon) lose mass and prolapse caudally toward the ground. The frog is an important structure of the foot that can suffer from various disorders such as thrush, canker, penetration and infection, avulsion, bruising, and atrophy.  It is also a great reference point for the farrier to locate the coffin bone and assess sole depth.  Duckett’s dot is a point on the cranial frog used to locate the tip of the coffin bone.  The collateral grooves are also used to help assess sole depth.

Bars of the Heels

-- The bars are extensions of the hoof wall that turn-in at the heel and run partway along the frog.  The bars strengthen the heel area and control overexpansion of the heels.  This area also contributes to building the sole of the hoof and helps support the horse’s weight. The bars start at the heel buttress and then taper down to blend in with the sole about the 1/2 mark of the frog.  They serve an important role in maintaining the integrity of the foot. The bars have several functions.  First, they provide a vertical stop for expansion of the hoof.  This means the hoof is supported as it is loaded.  Along with the heels, the bars prevent the hoof from over expanding as the foot is loaded and keep the foot from excessive vertical downward pressure.  The bars work in conjunction with the lateral cartilages of the foot to enable the foot to expand upon impact and dissipate energy to the lateral cartilages and digital cushion. Next, the bars provide traction, along with the heels.  Last, they act as brakes as they dig into the ground as the hoof is loaded to help stop forward movement of the foot and horse. Excessive trimming of the bars (and heels) will cause the hoof to descend and expand further than designed causing the sole to thin which can lead to bruising and inflammation of the foot. It can be difficult to know how the bar should be trimmed in an individual horse.  Certainly, trimming the bar below the surface of the sole can cause serious harm.  The bar may need to be higher in some horses that have weak hoof structures, i.e., the heels and/or the digital cushion.  Most horses are comfortable when the bars are a couple of millimeters higher than flush with the sole.  Concavity of the foot, type of footing, environmental moisture, and how healthy other hoof structures are may change how the bar requirements.  As the foot heals, the bar eventually returns to a more normal shape and size. Bar height may need to be removed if it is overgrown enough to cause excess pressure inside the foot or bars that have laid over are putting pressure on the sole, where they cause bruising and subsolar abscesses under the bars, which may permanently damage the underlying corium.  Bruising and abscesses of the bar and heel buttress are often called corns.  Bruising commonly occurs with no abnormalities present on the keratinized sole, although solar changes may be present ranging from some red staining of the inner solar epidermis (due to minor hemorrhage) to the palpable presence of serum either under the solar epidermis or seeping through to the outside.   If untreated, the affected area can become infected (i.e., a subsolar abscess).  Persistent, nonresponsive bruised sole dorsal to the apex of the frog suggests possible distal displacement of the distal phalanx secondary to laminitis. A corn is most common in the forefeet at the inner buttress and may be caused by improper placement of the shoe, a shoe left on too long, causing pressure on the buttress, and shoes that are fitted too closely/too small for the foot.  Corns are described as dry (only mild bruising), moist (serous exudate present), or suppurative (infected or abscessed). Bruising may be associated with lameness, depending on the severity. Long bars may grow inward at the ends, pinching the frog, affecting its growth and function, and leading to pain for the horse.  Bar material that lays over may trap debris, leading to abscesses, thrush, and white line disease. Broken bars are fractures of the caudal portion of the bar, where it unites with the wall.  The hoof expands in this area, so broken bars are painful.  Such bars come from unbalanced feet, excessive softening of the wall, and lack of frog contact with the ground. Being part of the hoof wall, the bars are also subject to the same wear and exfoliation as the outer layer and should be addressed as such.  Bars left too high have been implicated as a contributing factor in navicular syndrome, while bars trimmed too short are associated with weak and collapsed heels.  There is no “standard” when trimming the bars – or the entire hoof — and that the whole horse, his environment, and the current condition of the internal structures need to be considered.  It is not as simple as applying a standard rule to each hoof.  If bar material grows back quickly post trim, it is an indication that it needs to be there. The bars of the equine foot have several functions and should not be taken lightly.  Without them, the hoof will weaken, and the horse will become lame.  When too long, they may put pressure on the foot, trap debris, and cause lameness from hoof abscesses, thrush, white line disease, and bruising.

Underrun Heels

-- The foot of the horse is the foundation upon which it stands.  If the foot is not cared for properly, the horse will not be able to function to its full potential.  Underrun heels are all too common, and if uncontrolled will degrade the integrity of the hoof structure, leading to lameness issues.  To head off this problem, you should be familiar with causes, what they are, and what you can do to prevent them. Underrun heels are defined as when the angle of the heel is at least five degrees less than the angle of the toe.  Normal feet have toe and heel angles that are the same.  Basically, this is a long toe/short heel syndrome.  Severe cases may stand upon their heel bulbs.  The hoof-pastern axis is broken backward so that the slope of the hoof is greater than that of the pastern.  Radiographically, horses with underrun heels may have a flat coffin bone, or one that is lower at the heel than at the toe (negative palmar angle- normal horses have a slightly positive palmar angle). There are many contributing factors that cause or exacerbate underrun heels.

Conformation--A long toe/low heel conformation is one cause of underrun heels, and the Thoroughbred horse has such a foot quite commonly, though it may be seen in other breeds as well.  Normally, the hoof grows downward, but with long toe/low heel conformation, the hoof grows forward.  Since direction of heel growth follows direction of toe growth, as the toe becomes longer, the heel grows forward and drops lower. Horses with conformation flaws, such as long pasterns, might be more likely to develop underrun heels because of increased weight-bearing in the heels.

Shoeing and trimming--Improper shoeing and trimming is a common cause of underrun heels.  Most foals are born with good heels which are maintained until they go into training.  Trainers may ask farriers to lower a horse's heels and allow the toes to grow long, incorrectly believing that this will extend the horse's stride.  A shoe that is too small simulates the effect of a long toe because it places the weight-bearing surface of the foot in front of the vertical axis of the limb.  Similarly, the use of a toe-grab on a hoof that already has a long toe and low heel can increase the severity of underrun heels by increasing pressure on them.  Asymmetrical feet, irregular trimming or shoeing intervals, and allowing trimming or shoeing intervals to go beyond eight weeks are all causes of underrun heels.

Genetics—Many foals are born with or acquire the same foot conformation as one or both parents.  This could be because breeders tend to weigh other attributes more heavily than hoof conformation when making breeding decisions.

Nutrition--Nutritional deficits can exacerbate underrun heels simply by leading to lower hoof quality.  Horses with poor hoof quality may need added biotin and/or methionine in the diet.

Environment--Hooves that are exposed to extreme changes from dry to wet and/or unsanitary conditions might have loss of laminar strength.  The more wet the environment, the weaker the hoof wall.  When the strength of the heels is undermined, they are more readily able to reshape or collapse.

Workload-- Demanding performance requirements may cause underrun heels, particularly if the horse has other negative factors present.  Underrun heels and performance may reduce the horse’s lifespan. Poor hoof structure affects the hoof wall, which is essential to protecting the internal hoof structure from the demands of the horse's environment.  The heel plays a vital role in the hoof's structure, and larger problems may occur if the heel is not correct. The underrun heel structure leads to long-term effects; bruised heels, quarter and heel cracks, coffin joint synovitis, interference problems, and navicular disease may all occur. The long toe brings the heel forward and thus lower, bending the horn tubules at the heels.  When they become parallel to the ground, the ability to support the horse's weight is lost.  The poor quality of hoof wall at the heels no longer allows the heels to transfer concussion to other soft tissue supporting structures above the heels, such as the frog, digital cushion, deep digital flexor tendon, navicular bursa, and suspensory ligaments.  This can lead to bruising in the heels and associated soft tissues structures. The hoof wall at the heels becomes thin, and may collapse, and roll under the horse's foot, destroying the bars.  Corns and quarter or heel cracks appear.  With the heel out of commission, the frog, deep digital flexor tendon, and digital cushion take over more of the weight-bearing role than they are designed to handle. Increased tension in the deep digital flexor tendon increases pressure on the navicular bone and bursa, often leading to degeneration of those structures- navicular disease. Shoes further damage the heels when they rub against the shoe during the expansion phase of each step, wearing a trough in the shoe.  By contrast, the horse with a thick, solid heel base will not wear into the branches of the shoe on the bearing surface. Poor-fitting shoes inhibit growth of the hoof wall in the overstressed heel area, while the toe continues to grow.  This exacerbates the long-toe problem, increasing the distance from the point of the frog to the point of breakover. There now is delayed breakover with every stride, which creates more tension in the deep digital flexor tendon and can lead to interference problems such as overreaching, forging, or scalping.  The overlong toe acts like a mechanical lever arm, applying outward force to the horn tubules with every step.  The horn tubules in the toe area become bent, creating a "dish" (concavity) in the dorsal hoof wall, often accompanied by a toe crack. The bony column will now receive more concussion.  When the laminae inside the hoof wall stretch and tear, the bony column lowers into the hoof, thinning the sole and placing additional pressure on the blood vessels inside the foot.  The wings of the coffin bone can become lower than the coffin bone at the toe, increasing bruising and pain.  Then the toe will land first to protect the sore heel. Toe first landing leads to other problems.  The horse is more likely to stumble, and the white line will widen, leading to white line disease and abscesses.  This process can contribute to numerous hoof problems, causing the horse pain and effectively limiting his useful life. To limit the progress of underrun heels, the foot should be trimmed as close to the ideal foot as possible, then apply a shoe of some type.  An egg bar shoe is commonly used, but sometimes the heel will require additional support from pour pads or composite materials.  Wedge pads may maintain the pressure upon the heels, continuing to damage the internal structure.  In some cases, glue on shoes may be necessary to allow the heel to grow and to support the caudal portion of the foot.  These horses may need to be trimmed and shod every four weeks. Catching the problem early and taking steps to correct it makes the prognosis much more favorable, leading to a longer useful, pain free life for the horse.

Equine Hoof Fractures

-- Hoof cracks are fractures of the hoof wall.  They may occur at the toe, quarter, or heel of the hoof capsule.   These cracks may be superficial or deep and of various angles, horizontal and perpendicular to the coronet being the most common.  Like fractures of bone, some hoof cracks are more problematic than others. To understand hoof cracks, it is important to understand the structure and function of the hoof.  The horse stands on the phalanges of the third metacarpus/metatarsus, the bones of the hand and foot.  There is similarity, but more complexity of the hoof capsule compared to the human fingernail.  The hoof wall is divided into the toe, quarters, heels (or angles) and bars.  The toe is the front one-third and the quarters are the sides, while the heels are where the hoof wall folds back on itself at the end of each quarter to form the bars. The hoof must deform to loads placed upon it, though this may not be appreciated without slow motion cinematography. The frog is a triangular mass of keratinized tissue with a forward pointing apex and a base at the back of the foot.  Its appearance and consistency are similar to hard rubber.  It protrudes downward the ground between the bars of the foot.  There is a deep sulcus on each side, and a shallow sulcus (groove or cleft) in the base.  It should not be deep, nor should it extend into a crack between the heel bulbs. The outer hoof capsule (hoof wall) is made of insensitive keratinized tubules and intertubular matrix, comprising the epidermis, while the inner hoof capsule, or dermis, interdigitates with the former by its own living (sensitive) lamellae, which are, in turn, attached to the bone of the third phalanx.  It grows downward form the coronary dermis. The dermis is quite vascular and well supplied with nerves.  It may sometimes be called the corium, when referring to the foot. The nerves help to control blood flow, as well as sensation and placement of the foot.  The coronet (corona) is the region of the digit where the skin meets the hoof capsule.  It bulges slightly due to fat in the subcutaneous tissue and is called the coronary cushion.  There are numerous causes of hoof cracks, including the environment, nutrition, genetics (small feet, underrun heels, thin walls or soles, long toes) shoeing, trauma, and stable management.  Feet that are wet can imbibe water. The hoof should have a stiffness gradient, so that the stiffest tissue is external, and the least is internal.  When feet are chronically wet, the external tissue becomes weaker, and more prone to cracking.  The effects of a wet environment can begin to impact the hoof within 24 hours. Nutrition is difficult to control for in scientific studies due to the enormous number of other factors; however, biotin has been shown to improve hoof growth when fed for five months.  Overall quality may be affected, but the data has been inconclusive.  It would seem that horses on a good plane of nutrition have better hooves than those on poor nutritional diets. Hoof balance also plays a role.  Conformational defects create capsular distortion which weakens tissue, leading to hoof fractures.  Likewise, long toes cause increased bending of the horny tubules, which are then subject to failure.  Some cracks will start at the coronet due to damage to the coronary papillae leading to poor hoof quality, which is predisposed to fracture. Cracks at the toe may be due to coronet damage, severe hoof abscesses which undermine the hoof wall and break out at the coronet, compromised white line from laminitis, or chronically overgrown toes.  There may also be mechanical tearing from a club foot or other hoof deformity. Quarter cracks are often the result of short shoeing, long toes, underrun heels, medial to lateral hoof imbalance, injury to the coronary band, and thin hoof wall at the quarters.  These cracks often involve the dermis, are commonly infected, involve the dermis, and are lame.  Heel cracks are due to trauma, short shoeing, and the shoes being left on too long. Bar cracks are from these factors as well as lack of trimming. Horizontal cracks are parallel to the coronary band, and may be termed ‘blowouts’.  They are caused by severe abscesses that break out through the hoof wall or to trauma to the foot, causing disruption in horn production.  These are often not a big problem, but should be kept clean if they are deep.  Horizontal cracks will eventually grow out and be removed by trimming.  Those in the heel may catch on objects and rip the hoof, so they should be kept trimmed. Vertical cracks may begin at the top or the bottom of the hoof; at the coronet or at ground level.  They may be classified as superficial or full thickness.  The former are not associated with lameness as there is no dermal involvement.  These feet often do not have the correct moisture content, feet that go from wet to dry daily, or from poor nutrition.  Full thickness cracks are painful; the dermis is involved.  These cracks are unstable, being able to spread or pinch, or even have vertical movement when the horse bears full weight or picks up the foot.  There may be hemorrhage or purulent discharge.  Although many of these can be identified via simple thumb pressure or hoof testers, perineural anesthesia can help identify the area causing lameness. Treatment of cracks begins by evaluating the hoof quality, moisture content, wall thickness, hoof balance, and any dermal involvement, along with infection.  There are many treatment methods, meaning that horses should be treated as individuals, not by recipe.  As many cracks are from abnormal stresses on the hoof capsule, always start with balance.  Most will require a bar shoe.  If the crack is near the ground surface, the wall will need to be floated, or taken out of weight bearing to prevent stresses from promulgating the crack. Stabilization of the crack can be achieved via radiator horse clamps, wire to lace the crack, etc.  Deep cracks will need hoof repair composites to help fill in the open area, but care must be taken to not affect the dermis as these products produce heat when mixed.  There are various methods to protect the dermis.  The crack will need to be opened and cleaned prior to stabilization.  A bar shoe is placed for support and to decrease independent movement of the heels.  Clips may be placed on each side of the fracture to help limit hoof expansion.  If there is infection, it will need to be treated prior to placing any composite, which often takes only a few days, but in severe cases, may take several weeks. Most full thickness fractures will need to be laced with wire to support the composite.  This acts like reinforcing rods in concrete, strengthening the repair.  Local anesthesia and sedation are necessary.  Again, the corium will need to be protected by play-doh or putty, and a drainage tube may be necessary for seepage from the soft tissue underneath the hoof capsule. Cracks beginning at the ground may be trimmed out, as they are often from overgrowth of the hoof.  A groove should be created by rasping or burning above the crack by ¼ inch to help stop its perpetuation.  The groove isolates the crack as it follows the horn tubules. Fractures that begin at the coronet are difficult to treat, but the previous recommendation of balancing the hoof, a bar shoe, and hoof composite will help stabilize these cracks.  Heel cracks may be debrided and floated so that it is non-weight bearing.  Those heel cracks that begin at the coronet may need full foot support, including sole impression material to help prevent shearing and separation. These are only general recommendations, and consultation with an experienced farrier and veterinarian should be sought.  Radiographs can be helpful for some cracks, and, as mentioned previously, some will require perineural anesthesia and sedation. Some hoof fractures are so bad that the only choice is to remove the entire hoof wall behind the crack.  There may be significant soft tissue damage and infection in these cases.  Treatment with antibiotics is required, but soaking the foot will only lead to additional wet tissue, which may further weaken the wall.  In some cases, maggot debridement therapy may be helpful as they can remove dead tissue more completely and with less pain and hemorrhage than is caused by sharp debridement of tissue.

Common Questions and Answers

Hood, his colleagues involved with the Hoof Project, and other foot care professionals put forth frequently asked questions on equine feet for which they have given answers, and the logic behind the answers:

Q: Are white hooves weaker than dark hooves?
A: No. This is a statement that has been around for quite some time and is still commonly believed by many. Several studies have critically examined the question and all have produced the same results. There is no difference in strength or elasticity between white and dark hooves. It is likely that the impression that white feet are weaker came about because it is much easier to see defects--such as wall bruising and small cracks--in them than in dark hooves.

Q: Which is better, barefoot or shod?
A: There is no accurate answer to that question. To shoe or not to shoe a horse depends on many factors. The intended use of the horse, the previous shoeing history, the potential for problems in the feet, and the availability of a qualified farrier all impact the appropriate answer to this question. Because of the number of variables, it is necessary to answer the question for each horse as an individual rather than an absolute statement that applies to all horses.
One important part of this question is the ability of the foot--both internally and externally--to adapt to its environment. The foot of a horse that has never been shod and the foot of a horse that has always been shod will be different, as each has structurally adapted to the non-shod or shod state. It is for this reason that the occurrence of lameness is not uncommon when horses are shod for the first time as well as when those that have always worn shoes are left unshod.

Q: What causes white line disease?
A: The first theory as to the underlying cause of white line disease is that it is due to a fungus that invades and destroys the non-pigmented regions of the inner hoof wall. It is usually assumed the route of entry is the foot's solar surface. The second most popular theory is that fungi (or bacteria) are present, but that some other insult, such as trauma, is required before they can invade and damage the hoof wall. A third school of thought is that white line disease is a consequence or form of chronic laminitis. More recently, it has been proposed that white line disease is a metabolic disease in which the cells of the wall's inner layers of the hoof are prematurely aging.

Q: What causes a frog to fall off?
A: Most frogs have the tendency to shed or come off periodically. This can occur so that it looks like the entire frog is being lost at one time. The frog of the horse's foot--like the hoof wall, sole, bulbs, and periople--are composed of highly modified skin. Compared to soft skin, these hoof structures are biochemically unique in that the individual cells that make them up are cemented together so that loss of individual cells occurs rarely or very slowly. This allows the hoof components to grow outward or downward until it is either cut away by the farrier or worn away by contact with the ground. Some frogs have a tendency to shed or come off periodically. When this happens, it is only the outer layers that are shed so that there is ample frog left with the foot. This appears to be a normal way for the frog to control its thickness.

Q: What causes the white, flaky appearance sometimes seen on the upper part of the hoof wall (coronary band)?
A: The outer-most layer of the hoof wall is technically known as the stratum externum and is often called hoof varnish. Like the rest of the hoof wall, it is produced at the coronary band and grows down the wall. Except for its thinness, it is similar in structure to the rest of the hoof wall, but biochemical differences do exist between this outer layer and the rest of the hoof wall. When this layer gets thicker than normal, it wears away. As it dries out, it tends to turn white and flake off. By itself, the condition poses little problem to the horse, but its cause should always be investigated.

Q: What's normal hoof size?
A: This one is answered by Doug Butler, PhD, American Farrier's Association Certified Journeyman Farrier, Fellow of the Worshipful Company of Farriers, who has written books on equine feet and hoof care and has been quoted in this magazine and others in the past. A hoof that is proportional to the horse's body size, he has declared, allows for the ideal distribution of body weight over the foot's laminar surface. When the foot is proportional to body size, he explains, it prevents over-compression of the sensitive and bony structures and allows the hoof to expand normally during movement.
Hoof size, he says, is influenced both by heredity, management, and nutrition. Horses fed an optimum diet, he avers, have an 80% increase in hoof-sole-border area size compared to those fed a limited diet.

Q: What influences a hoof's growth rate?
A: Butler says first that the rapidly growing hoof is often the healthier one, and that young horses have a higher hoof growth rate than older horses. Warm temperatures produce a higher hoof growth rate than cold temperatures. Exercise can increase growth rate, and front hooves generally grow faster than rear hooves. Generally speaking, the average rate of growth is about three-eighths of an inch or one centimeter per month. Growth rate can also be affected by hoof trauma and injury. Vitamin A is essential for proper hoof growth and health. Also essential is moisture, although an excessive amount of moisture in the hoof can be unhealthy.

Take-Home Message

In summary, it is obvious that ongoing hoof care is essential in maintaining good feet in our horses. It also is obvious that not all feet are created the same and that foot care should be carried out on an individual basis, based on each individual's normal foot conformation and anatomy.