Horse hoof
Encyclopedia
Phalanx bones
In anatomy, phalanx bones are those that form the fingers and toes. In primates such as humans and monkeys, the thumb and big toe have two phalanges, while the other fingers and toes consist of three. Phalanges are classified as long bones.The phalanges do not have individual names...
of the 3rd digit (digit III of the basic pentadactyl limb of vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, evolved into a single weight-bearing digit in equids) of each of the four limbs of Equus
Equidae
Equidae is the taxonomic family of horses and related animals, including the extant horses, donkeys, and zebras, and many other species known only from fossils. All extant species are in the genus Equus...
species, which is covered by complex soft tissue and keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
ised (cornified) structures. Since a single digit must bear the full proportion of the animal's weight that is borne by that limb, the hoof is of vital importance to the horse. The phrase "no hoof, no horse" underlines how much the health and the strength of the hoof is crucial for horse soundness.
Hooves in the natural state
Both wild and feral equid hooves have enormous strength and resilience, allowing any gait on any ground. A common example of the feral horse type is the MustangMustang (horse)
A Mustang is a free-roaming horse of the North American west that first descended from horses brought to the Americas by the Spanish. Mustangs are often referred to as wild horses, but there is intense debate over terminology...
. The Mustang is, in part, descended from the Iberian horse
Iberian horse
The Iberian horse is a title given to a number of horse breeds native to the Iberian peninsula. At present, 17 horse breeds are recognized by FAO as characteristic of the Iberian Peninsula....
s brought to the Americas by the Spanish
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, but most herds also have ancestry from other breeds. Therefore, the famous Mustang hoof strength is in part a result of natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
and environment. Thus, it is proposed that other domestic breeds could develop similar hooves if raised under similar conditions.
The recent barefoot movement claims that such a strength can be almost completely restored to domesticated horses, when appropriate trimming and living conditions are applied, to such an extent that horseshoe
Horseshoe
A horseshoe, is a fabricated product, normally made of metal, although sometimes made partially or wholly of modern synthetic materials, designed to protect a horse's hoof from wear and tear. Shoes are attached on the palmar surface of the hooves, usually nailed through the insensitive hoof wall...
s are no longer necessary in almost any horse. If true, it would undermine the belief that "the horseshoe is a necessary evil."
The barefoot management system has not, however, gained a foothold among serious equine professionals, due to the increased strain placed on the hoof in sports, such as eventing
Eventing
Eventing is an equestrian event comprising dressage, cross-country, and show jumping. This event has its roots in a comprehensive cavalry test requiring mastery of several types of riding...
and endurance riding.
Anatomy
Pedal bone
The pedal bone, commonly known as the coffin bone , is the bottommost bone in the equine leg and is encased by the hoof capsule. Also known as the distal phalange, third phalange, third phalanx, or "P3"....
, PIII). Palmarly/plantarly, it covers and protects specialised soft tissues (tendons, ligaments, fibro-fatty and/or fibrocartilaginous tissues and cartilage). The upper, almost circular limit of the hoof capsule is the coronet (coronary band), having an angle to the ground of roughly similar magnitude in each pair of feet (i.e. fronts and backs). These angles may differ slightly from one horse to another, but not markedly. The walls originate from the coronet band. Walls are longer in the dorsal portion of the hoof (toe), intermediate in length in the lateral portion (quarter) and very short in palmar/plantar portion (heel). Heels are separated by an elastic, resilient structure named the 'frog'. In the palmar/plantar part of the foot, above the heels and the frog, there are two oval bulges named the 'bulbs'.
When viewed from the lower surface, the hoof wall's free margin encircles most of the hoof. The triangular frog occupies the center area. Lateral to the frog are two grooves, deeper in their posterior portion, named 'collateral grooves'. At the heels, the palmar/plantar portion of the walls bend inward sharply, following the external surface of collateral grooves to form the bars. The lower surface of the hoof, from the outer walls and the inner frog and bars, is covered by an exfoliating keratinised material, called the 'sole'.
Just below the coronet, the walls are covered for about an inch by a cornified, opaque 'periople' material. In the palmar/plantar part of the hoof, the periople is thicker and more rubbery over the heels, and it merges with frog material. Not all horses have the same amount of periople. Dry feet tend to lack this substance, which can be substituted with a hoof dressing.
Characters and functions of the external hoof structures
The walls
The walls are considered as a protective shield covering the sensitive internal hoof tissues (like the exoskeletonExoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
of arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s), as a structure devoted to dissipating the energy of concussion, and as a surface to provide grip on different terrains. They are elastic and very tough, and vary in thickness from 6 to 12 mm. The walls are composed of three distinct layers: the pigmented layer, the water line and the white line.
The pigmented layer is generated by the coronet, and its color is just like that of the coronet skin from which it is derived. If the coronet skin has any dark patch, the walls show a parallel pigmented line, from the coronet to the ground, showing the wall's growth direction. This layer has predominately protective role, and is not as resistant to ground contact, where it can break and flake away.
The water line is built up by the coronet and by the wall's corium (the living tissue immediately beneath the walls). Its thickness increases proportionally to the distance from the coronet and, in the lower third of the walls, is thicker than the pigmented layer. It is very resistant to contact to the ground, and it serves mainly a support function.
The white line is the inner layer of the wall. It is softer and fibrous in structure and light in color; white in a freshly trimmed hoof, yellowish or gray after exposure to air and dirt. From the underside of the healthy hoof, it is seen as a thin line joining the sole and the walls. The white line grows out from the laminar connections. Any visible derangement of the white line indicates some important derangement of laminar connections that fix the walls to the underlying P3 bone. Since the white line is softer than both the walls and the sole, it wears fast where it appears on the surface; it appears as a subtle groove between the sole and the walls, often with some debris or sand inside.
The three layers of the wall merge in a single mass and they grow downwards together. If the wall does not wear naturally, from sufficient movement on abrasive terrains, then it will protrude from the solar surface. It then becomes prone to breakage, and the healthy hoof will self-trim, by breaking or chipping off.
When a horseshoe is applied, it is fixed to the wall. Nails are driven in, oblique to the walls. They enter the wall at the outside edge of the white line and they emerge at the wall's surface, about 15 to 20 mm from the base of the wall.
The wall is anatomically analogous to the human finger or toe nail.
The frog
The frogFrog (horse)
The frog is a part of a horse's hoof, located on the underside, which should touch the ground if the horse is standing on soft footing. The frog is triangular in shape, and extends from the heels to mid-way toward the toe, covering around 25% of the bottom of the hoof...
is a V shaped structure that extends forwards across about two-thirds of the sole. Its thickness grows from the front to the back and, at the back, it merges with the heel periople. In its midline, it has a central groove (sulcus
Sulcus
Sulcus may refer to:* Sulcus , a groove, crevice or furrow in medicine, botany, and zoology* Sulcus , a long parallel groove on a planet or a moon-See also:...
), that extends up between the bulbs.
It is dark gray-blackish in color and of a rubbery consistency, suggesting its role as shock absorber and grip tool on hard, smooth ground. Actually, the frog acts like a pump to move the blood back to the heart, a great distance from the relatively thin leg to the main organ of the circulatory system.
In the stabled horse, the frog does not wear, but degrades, due to bacterial and fungal activity, to an irregular, soft, slashed surface. In the free-roaming horse, it hardens into a callous consistency with a near-smooth surface.
It is anatomically analogous to the human fingertip.
The frog can also be referred to as the subhoof. Sub meaning below or under. Therefore literally meaning the part below the hoof.
The sole
The sole has a whitish-yellowish, sometimes grayish color. It covers the whole space from the perimeter of the wall to the bars and the frog, on the underside of the hoof. Its deep layer has a compact, waxy character and it is called 'live sole'. Its surface is variable in character as a result of ground contact. If there is no contact, as in shod hooves or when the walls are too long or the movement poor, the lower surface of the sole has a crumbly consistency, and it is easily abraded by scratching it with a hoofpick. Conversely, it has a very hard consistency, with a smooth, bright surface, when there is a consistent, active contact with the ground. The front portion beneath the front of the pedal bone is called the 'sole callus'.A stone bruise affects the sole
Sole (foot)
The sole is the bottom of the foot.In humans the sole of the foot is anatomically referred to as the plantar aspect. The equivalent surface in ungulates is the hoof.- Human sole :...
of the horse's
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
foot. It is often caused by a horse treading on a stone or sharp type of object, landings from high jumps and excessive exposure to snow. A major symptom is lameness
Lameness (equine)
Lameness in horses and other equidae is a term used to refer to any number of conditions where the animal fails to travel in a regular and sound manner on all four feet...
.
The bars
Bars are the inward folds of the wall, originating from the heels at an abrupt angle. The strong structure built up by the extremity of the heel and of the bar is named the 'heel buttress'. The sole between the heel walls and the bars is named the 'seat of corn', and it is a very important landmark used by natural hoof trimmers to evaluate the correct heel height. The bars have a three-layer structure, just like the walls (see above). When overgrown, they bend outwards and cover the lower surface of the sole.Internal structures
Pedal bone
The pedal bone, commonly known as the coffin bone , is the bottommost bone in the equine leg and is encased by the hoof capsule. Also known as the distal phalange, third phalange, third phalanx, or "P3"....
; P3;) is completely (or almost completely) covered by the hoof capsule. It has a crescent shape and a lower cup-like concavity. Its external surface mirrors the wall's shape. The corium, a dermo-epidermal, highly vascularized layer between the wall and the coffin bone, has a parallel, laminar shape, and is named the laminae. Laminar connection has a key role in the strength and the health of the hoof. Beneath the rear part of the sole, there is the digital cushion, which separates the frog and the bulb from underlying tendons, joints and bones, providing cushioning protection. In foals and yearlings, the digital cushion is composed of fibro-fatty, soft tissue. In the adult horse, it hardens into a fibro cartilagineous tissue when sufficient, consistent concussion stimulates the back of the hoof. Normal transformation of the digital cushion into fibrocartilagineous tissue is now considered a key goal, both for prevention of, and for rehabilitation of recovering cases of navicular syndrome http://www.hoofrehab.com. The flexor tendon lays deeper, just along the posterior surface of the small pastern
Pastern
The pastern is a part of the leg of a horse between the fetlock and the top of the hoof. It incorporates the long pastern bone and the short pastern bone , which are held together by two sets of paired ligaments to form the pastern joint...
bone (PII) and navicular bone
Navicular bone
The navicular bone is a small bone found in the feet of both humans and horses.- Human anatomy :The navicular bone is one of the tarsal bones, found in the foot. Its name derives from the bone's resemblance to a small boat, caused by the strongly concave proximal articular surface...
, and it connects with posterior surface of P3; the navicular functions as a pulley.
The hoof mechanism
The shape changes in a loaded hoof are complex. The plantar arch flattens, the solar concavity decreases in depth and heels spread. The hoof diameter increases to a 'dilated' configuration and P3 drops marginally into the hoof capsule. There is some recent evidence that a depression takes place in this phase, with blood pooling ('diastolic phase') mainly into the wall corium. When unloaded, the hoof restores its 'contracted' configuration, the pressure rises and the blood is squeezed out ('systolic phase'). There is a secondary pumping action, with the flexion of the foot, as it is raised.
The hoof mechanism ensures an effective blood circulation into the hoof, and it aids general circulation, too.
Time-related changes of the hoof
Hooves have to be considered as a plastic structure and their time-related, very complex changes can be considered in the short term (days/weeks), in the medium term (the horse's lifespan) and in the long term (the evolution of equids).Hoof changes in the short term
Just like the cornified layer of epidermis and of any mammalian nail, the hoof capsule is created only from epidermis, the outer living layer of the skin. From a microscopic point of view, epidermis is a multi-layered, specialised cornifying epithelium. It overlays the dermis, and it is separated from it by a basal lamina. It has no blood vessels and living cells acquire their oxygen and nutrients by fluid exchanges and molecular diffusion, from underlying dermis, flowing into microscopical spaces among individual cells. Products of metabolism are cleared by a reverse of this process. Epidermis growth take place by mitoticMitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
activity in its deepest layer, into the basal layer, with slow outward migration and maturation of cells. As these cells approach the surface, special proteins accumulate into their cytoplasm, then the cells die and 'dry', into microscopic, tightly-connected individual layers, composed mainly of keratin. The resulting 'dead' superficial layer serves a protective function, saving underlying living tissues from injury, from dehydration and from fungal and bacterial attack. The constant thickness of the cornified layer results most commonly from regular superficial exfoliation. When a specialised cornified structure has a particular toughness, as in nails and hair, little or no exfoliation occurs and the cornified structures must slowly migrate away from their original position.
Thus, the specialised cornified structures of the hoof are the wall, the sole, the frog and periople. The wall does not exfoliate at all; it is constantly growing downward (about 1 cm per month), and self-trims by wearing or chipping by ground contact, in wild and feral horses. Solar, frog and periople material grow outwards and exfoliate at the surface by ground contact and wearing. In the domesticated horse, movement and typical ground hardness are insufficient to allow self-trimming, so humans have to care for them, trimming the walls and the frog, and scraping off the dead sole.
Hoof changes in the medium term
Front and hind hooves are identical in the foal, but differ visibly in the adult horse. This is good evidence of medium-term plasticity of the whole hoof shape, as a result of variation in its use. Slow changes in hoof shape occur under any consistent change in the horse's movement pattern and under a wide variety of pathological conditions. They can be seen now as a clear example of a complex adaptive systemComplex adaptive system
Complex adaptive systems are special cases of complex systems. They are complex in that they are dynamic networks of interactions and relationships not aggregations of static entities...
, a frequent feature of living beings and structures.
Self-adapting capabilities of the hooves show their maximal effectiveness in wild equids (but domesticated horses show this too, to a lesser extent), as shown by the perfect soundness of feral horses, such as Mustang
Mustang (horse)
A Mustang is a free-roaming horse of the North American west that first descended from horses brought to the Americas by the Spanish. Mustangs are often referred to as wild horses, but there is intense debate over terminology...
s, in a wide variety of environments.
Hoof changes in the long term
Equid hooves are the result of the 55-million-year evolution of the horseEvolution of the horse
The evolution of the horse pertains to the phylogenetic ancestry of the modern horse from the small dog-sized, forest-dwelling Hyracotherium over geologic time scales...
. Wild and domesticated Equus species share a very similar hoof shape and function. The present-day conformation of the hoof is a result of a progressive evolutionary loss of digits I, II, IV and V of the basal pentadactyl limb, with changes in bones, joints and hoof capsule. The resulting conformation allows a heavy, strong body to move with high speed on any ground, and most efficiently on open, hard, flat areas like prairies and deserts (i.e., 'cursorial specialisation').
See also
- Natural hoof careNatural hoof careNatural hoof care is the practice of keeping horses so that their hooves are worn down naturally and so do not suffer overgrowth, splitting and other disorders...
- Equine forelimb anatomyEquine forelimb anatomyThe equine forelimb of the horse is attached to the trunk of the animal by purely muscular connections...
- FarrierFarrierA farrier is a specialist in equine hoof care, including the trimming and balancing of horses' hooves and the placing of shoes on their hooves...
- Evolution of the horseEvolution of the horseThe evolution of the horse pertains to the phylogenetic ancestry of the modern horse from the small dog-sized, forest-dwelling Hyracotherium over geologic time scales...
- HorseshoeHorseshoeA horseshoe, is a fabricated product, normally made of metal, although sometimes made partially or wholly of modern synthetic materials, designed to protect a horse's hoof from wear and tear. Shoes are attached on the palmar surface of the hooves, usually nailed through the insensitive hoof wall...
External links
- Horse Hoof Care Information Horse Hoof Care Net (CA)
- American Farrier's Association American Farrier's Association
- How a Horse Hoof Grows from eXtension