An overview of the equine distal limb; including distal limb anatomy and external factors impacting the health and condition of the hoof and distal limb

Jennifer Stoltz

Tuesday June 20th, 2017

The equine distal limb and hoof capsule are critical to the overall health and well-being of the horse.  Through understanding the anatomy and external factors, one can have a greater understanding of how to best provide care for the horse as a whole.  As a barefoot trimmer it is critical to understand the functional anatomy and understand how different styles of trimming or shoeing will impact the anatomy and locomotion of the horse.

Bones

The distal limb, defined as the equine limb below the knee in the front end and below the hock in the hind end, is made up of 9 bones (Romenanko, 2017).  The equine distal limb is unique from many other mammals as there are no muscles in the distal limb.  This means that each bone and ligament and tendon have very important roles to play in the equine’s locomotion.  The bones in the equine distal limb can be grouped into three metacarpal bones, three sesamoid bones and three phalanx bones (Romenanko, 2017).

Metacarpal Bones

The second, third and fourth metacarpal bones are in the distal limb (the first metacarpal is higher up the leg).  The second and fourth metacarpal bones are commonly known as splint bones and are located on either side of the third metacarpal bone, commonly known as the cannon bone (Romenanko, 2017).

The second metacarpal bone is located on the inside of the leg and the fourth metacarpal bone is located on the outside of the limb.  The splint bones are typically free from the cannon bone, however it is common in older or well used horses to develop “splints”. This common ailment is when the splint bones fuse in one or more location to the cannon bone; this does not typically cause lameness issues (Romenanko, 2017).

The cannon bone has a ridge on the diatal articular surface that is often the location in which small “screwdriver” fractures occur (Romenanko, 2017).  This type of fracture on the cannon bone are thought to be a result of bone fatigue (Whitton, 2010).  The bone heals through modeling and remodelling.  Modelling heals the bone by adding bone material and volume to the bone without removing any of the damaged bone although this is a bodily function intended to compensate for the fragile bone, modelling does not adequately off set the damage done.  Bone remodelling heals fatigued or damaged bone through replacing old bone material with new bone material adding strength back into the bone (Witton, 2010).  Regular intensive loading of the distal limb decreases the ability for the horse to remodel their bone; without the ability to remodel the bone, modeling is the only process for the horse to heal the bones in their distal limb, increasing the likely hood of fatigue fractures (Whitton, 2010.  This is commonly seen as screwdriver fractures in the cannon bone of racehorses and other high performance equine athletes (Whitton, 2010).

Sesamoid Bones  

There are two related sesamoid bones (medial proximal sesamoid bone and lateral proximal sesamoid bone) that are located on the palmar side of the MCP joint between the cannon bone and the proximal phalanx bone (Romenanko, 2017).  The third sesamoid bone is called the navicular bone, and is located in the hoof capsule on the palmar side of the DIP joint between the middle phalanx and the distal phalanx bones.

The medial proximal and lateral proximal sesamoid bones act as similar to a pulley, aiding in the function of the deep digital flexor tendon (Cornelissen, 2002).  However, the torque on these small bones often results in an ailment called sesamoiditis; a degenerative bone disorder impacting medial proximal sesamoid bone and lateral proximal sesamoid bone as well as the surrounding area (Cornelissen, 2002).  Sesamoiditis is diagnosed through identifying intermitted lameness of a particular limb, then performing radiographs.  Radiographs may depict widened vascular channels, irregularity of bone structure and the presence of osteophtes (Cornelissen, 2002).  It is though that the primary cause of this degenerative disorder is due to high impaction, yet the exact cause is unknown.

The navicular bone has two primary functions associated with blood flow and locomotion.  The navicular is a small spindle shaped bone with only two surfaces, covered in the hyaline cartilage (Belknap, 2017).  This small bone articulates between the middle phalanx and the distal phalanx bones, like the medial proximal and lateral proximal sesamoid bones, the navicular also facilitates the movement of the of the deep digital flexor tendon (Belknap, 2017).

The navicular bone also has two grooves through the bone where arteries pass through, allowing the flow of blood in and out of the hoof capsule and the whole distal limb (Belknap, 2017).  The horse’s heart is not strong enough to pump blood all the way back up each leg, so the navicular bone and the frog aid in blood flow.  The paired palmar digital vessels extend through the navicular bone channels and the navicular bone acts as a pump as the bone articulates with the horse’s locomotion, it crimps and opens the arteries (Belknap, 2017).  This function pushes the blood into the distal phalanx and then the soft tissue of the hoof capsule, first the laminae, digital cushion and finally the frog, where the blood moves back through the navicular bone and up the limb (Belknap, 2017).  Although not accurate to how the process works, the frog is often colloquially referred to as the fifth heart because of the pumping action that occurs in each limb.

Navicular disease is a common ailment in horses who have shoes put on at a young age.  The contracted heels and upright hoof angles, which are associated with shoeing decrease the navicular bones’ ability to pivot (Romenanko, 2017).  This will impact the way in which blood flows through the hoof capsule and will erode both the navicular bone and will often cause stalking up of the distal limb (swelling in the soft tissue surrounding the cannon bone and proximal and middle phalanx bones (Romenanko, 2017).  Navicular disease not only causes permanent on and off lameness for the horse, but will also impact the blood flow in the limb, increasing blood flow into the limb and decreasing blood flow out of the limb (Romenano, 2017).

Phalanx Bones  

            The equine distal limb has three phalanx bones, the proximal phalanx (P1) commonly known as the long pastern, the middle phalanx  (P2) commonly known as the short pastern and the distal phalanx (P3) commonly known as the coffin bone (Belknap, 2017).  Both the P1 and P2 bones rarely suffer from injury or degeneration issues.  However, they are connected by a complex network of ligaments that aid in the stabilization of the distal limb and hoof capsule, allowing horses to comfortably traverse across uneven footing without major injury (Belknap, 2017).  However P3 or coffin bone, is related to a large number of potential ailments in the distal limb; including ring bone and side bone, founder and a variety of fractures (Romenanko, 2017).

The coffin bone has three surfaces, the articular surface, solear surface and the parietal surface.  The junctions between these surfaces aid in different processes.  For example, the coronary boarder (made up of the articular and parietal surfaces at the dorsal aspect of the limb) aids during the extensor phase of locomotion (Belknap, 2017).  The parietal surface of the bone is very rough, allowing the soft tissue to attach itself to the bone.  The coffin bone as a whole also has a large amount of bone perforations, allowing blood to pass from the navicular bone into the soft tissue (Belknap, 2017).

The coffin bone has two rhomboid shaped ungual cartilages dorsally located on both the inside and outside of the bone called the collateral cartilages; this cartilage is thicker distally than proximally (Belknap, 2017). Ring bone or side bone occur when some (side bone) or all (ring bone) of the collateral cartilage undergoes calcification (Romenanko, 2017).  In a healthy hoof capsule, the cartilage is immediately proximal to the bars of the hoof and will cause significant pain if calcification occurs.  The cartilages exact function and interaction with the coffin bone are realatively unknown; however, it is known that the cartilage helps during the loading phase of stance through expansion and contraction (Belknap, 2017).  These two cartilages are connected to each other by a hammock like structure that is located just above the bars on the inside of the hoof capsule (Romenanko, 2017).  When the bars are left to get too long due to improper trimming or shoeing, they can create pressure on the bottom of this hammock forcing the cartilage out of place; creating bulges in the pastern area of the horse’s leg.  The coffin bone is also susceptible to foundering; founder occurs when the coffin bone rotates down (Belknap, 2017).   Many people in the horse industry use the words founder and laminitis interchangeably, however this is inaccurate.  Founder impacts the bone and is often a result of a laminitis episode that can be brought on by a variety of imbalances in the horse’s body (Romenanko, 2017).

Tendons and Ligaments

The horse’s distal limb has incredibly complex set of tendons and ligaments, entire textbooks have been written on this subject alone.  The primary ligaments are the check ligament and the suspensory ligament, the primary tendon groups are the suspensory and extensor tendons.  Although there are several other ligaments including the annular ligaments, sesamoid ligaments, medial patella ligament and others these smaller groups of ligaments are primarily for stabilization rather than for locomotion (Romenanko, 2017).

Ligaments

The set of check ligaments are composed of superficial check ligament and the inferior check ligament.  Although these two ligaments are in the same general location, the superficial check ligament is closer to the outside of the leg, while the inferior check ligament in tucked underneath (Ramey, 2011).  The check ligament set begins behind the knee and attached along the radius of the cannon bone.  The check ligaments is tucked between the two splint bones, and can become damaged if the splint bones fuse to the cannon bone (as discussed previously) (Ramey, 2011).  The inferior check ligament connects directly to the deep digital flexor tendon and the superficial check ligament connects to the superficial flexor tendon (Romenanko, 2017).  The check ligaments’ main function is to disable the function of the flexor tendons, limiting the movement a horse is able to experience in the forward motion of their locomotion (Ramey, 2011).  This limiting function allows the horse to avoid tendon injury due to overextension.   The secondary function of the check ligaments are to interact with the check apparatus.  The check apparatus is the mechanism which allows horses to sleep in a standing position (Ramey, 2011).  As the horse begins to relax into sleep, the check apparatus automatically engages, preventing the horse from losing balance.  The check ligaments act as a tension band locking the knee.  In the hind end the check ligament hooks around a small boney area in the stifle joint (Ramey, 2011).  In the hind end, a secondary stabilization ligament, the medial patella ligament, also hooks onto the boney area in the stifle joint to prevent the hind end from falling or collapsing during sleep (Ramey, 2011).

Another primary ligament is the suspensory ligament, this ligament’s main purpose is to cushion the impact of concussion created during locomotion and overextension.  The suspensory ligament supports the fetlock from sinking past the point of over extension (Trump, 2014).  The suspensory ligament begins at the top of the cannon bone and ends on the upper third of the P2 bone and is the widest ligament in the leg (Trump, 2014).  At the medial proximal and lateral proximal sesamoid bones, the suspensory ligament separates into two bands.  The splitting action of this ligament allows both the medial proximal and lateral proximal sesamoid bone to interact and influence the horse’s the locomotion (Trump, 2014).

Injuries to the suspensory ligament are very common in equine athletes and are often a serious prognosis. Suspensory injuries are a leading soft tissue injury in domestic horses, and most commonly in the foreleg.  Racehorses commonly have suspensory ligament injuries that often results in euthanasia (Trump, 2014).  Although most horses can continue to live a comfortable life after a suspensory injury, they will never gallop again, so most owners choose to put the horse down, rather than pay for a long and expensive recovery (Trump, 2014).

Horses who participate in eventing (a single or three day triathlon like competition which includes a dressage phase, stadium jumping phase and cross-country jumping phase) are the most likely group of horses to suffer from suspensory ligament injuries (Trump, 2014).  Event horses are so susceptible to suspensory injuries due to their need to both regularly gallop at high speeds and jump, both activities pushing both the horse and their ligaments to the far end of their limit.  In a study of 1,527 horses there was 52 event horses and 92% of them suffered from suspensory injuries in varying degrees (Trump, 2014).  A suspensory injury can occur in an acute injury, where the fetlock can be visually seen sinking much lower to the ground than normal, in some cases it can even drop to touch the ground; a suspensory injury can also occur in chronic scenario, where the ligament is damaged slowly over a long period of time (Trump, 2014).

Tendons         

There are two flexor tendons that stretch down the back of the equine limb.  The superficial digital flexor tendon is on the outside of the horse’s leg and the deep digital flexor tendon is underneath it (Sullivan, 2007).  The flexor tendons aid in bending the joints of the leg moving the horse’s leg backward.   This tendon is under more stress then the extensors as both flexor tendons are weight bearing during rest and during locomotion.  The flexor tendons are also under stress because they are extended during the first weight bearing action of the stance phase (Sullivan, 2007).

The superficial flexor tendon provides the “spring” during movement.  In high level equine athletes this tendon is often pushed to its limit as the spring gives the horse the competitive edge during galloping and / or jumping (Sullivan, 2007).  The superficial flexor tendon is the second most common soft tissue injury in equine athletes (Trump, 2014).

Dressage horses (a flat style of riding that asks the horse and rider to perform complex movements on the flat) more commonly have deep digital flexor tendon injuries (Sullivan, 2007).  Deep digital flexor tendon injuries are more commonly chronic and occur over a long period of time, compared to superficial digital flexor tendon injuries which commonly occur in acute situations (Sullivan, 2007).  Both the superficial and deep digital flexor tendon injuries are seen as “bowed tendons” that are caused by tearing and swelling of the tendon, causing it to visually bulge or “bow” outward on the distal limb.  The swelling often takes 1 – 3 weeks to go down enough to make a clear assessment of the severity of the injury (Sullivan, 2007).

The digital extensor tendons originate at the superficial flexor muscle, just behind the horse’s elbow in the front end and the stifle in the hind end.  This tendon also splits around the medial proximal sesamoid bone and lateral proximal sesamoid bone but is located on the front of the limb, and connect to the P3 bone (Butcher, 2007).  This tendon aids in the extension of the foreleg during locomotion and is not weight bearing when the horse is at rest. This tendon is not often subject to injury or stress (Sullivan, 2007).

Tendon injuries can be classified in four types: type one is when the tendon is enlarged but only appears slightly dark on the ultrasound; type two is the disruption of the tendon fibre and injury is seen as some dark spots on the ultrasound; type three is some tearing of the tendon fibre and is seen as mostly dark spots; type four is when the tendon fibres are torn and filled with blood, which will appear as complete black on the ultrasound (Dyson, 2011).

Although these primary tendon and ligaments are relatively well understood, the complex network of tendons and ligaments in the equine distal limb have barely begun to be understood (Dyson, 2011).  In a study by Dyson (2011) new fibrous bundles on the accessory ligament of the deep digital flexor tendon.  This relatively recent discovery is an indication that more research is needed in order to fully understand the complex nature of the equine limb.  It is speculated that further research has not been conducted due to the high cost of research and the comparatively low financial benefit that may come from a study (Dyson, 2011).

Hoof Capsule Anatomy

            The anatomy of the hoof capsule has five primary functions; shock absorption, circulation, traction, protection and protein and waste excretion. In order to achieve this, the hoof capsule has a unique anatomy.  Looking at the underside of the hoof, one can see the wall, the outer support structure, which can also be seen from the outside of the hoof.  This part of the hoof is made out of a horn structure (Romenako, 2017).  The next visible part of the anatomy is the white line.  The white line is the dead lamina and corium that have grown out.

When the hoof is radiographed there is are two visible layers: superficial radiographic layer and deep radiographic layer.  The superficial radiographic layer is made up of the stratum externum and the stratum medium.  The stratum externum is commonly known as the periopal and is a very thin waxy, protective layer.  The stratum medium is the bulk of the wall horn (Goulet, 2015).  The deep radiographic layer is made up of the stratum internum and the dermis parietis.  The stratum internum is the lamina layer and the dermis parietis is the corium layer (Goulet, 2015).

The lamina have several functions within the hoof capsule; connection, cushioning and filtering.  There is a layer of lamina on the P3 bone, called the dermis parietis or corium layer and the stratum internum or lamina layer is attached to the stratum externum or wall.  Although these two layers have different names, they have almost the same function (Romenanko, 2017).  These two layers interlock to create a strong connecion between the supporting structures (hoof wall) and the internal structures (P3 bone) (Romenanko, 2017).  Due to the fact that these layers are interlocking rather than connecting, they aid in the expansion and contraction of the hoof that reduce impact force on the limb (Ramey, 2011).  The dermis parietis and stratum internum give the hoof capsule the unique ability to be simultaneously strong and flexible (Ramey, 2011).

The lamina structures (both dermis parietis and stratum internum) are influential in the blood flow patterns of the hoof capsule.  As the blood flows through the lamina, excess proteins and toxins are filtered from the blood (Ramey, 2011).  These proteins and toxins are then excreted from the body in the form of horn, seen as wall growth.

When a horse’s body experiences changes within in their body, the horn on their hoof will tell the story through various rings and varying tightness or looseness of horn tubules (Ramey, 2011).  Factors that can cause wall rings include but are not limited to deworming, use of medication, diet change, exercise or weight change and season change (Ramey, 2011).  A study by Lewis et al (2014), found that seasonality had a significant impact on the growth rate of the hoof wall.  The growth rates in their study were highest in the fall, followed by the spring, summer and the slowest growth occurred in the winter (Lewis, 2014).

Laminitis is a common ailment that occurs in domestic horses. This disease can be caused by a multitude of factors, including nutritional deficiencies or abundances, stress, infection, obesity, acute trauma, chronic mechanical issues, Cushing’s disease, corticosteroids, hormone imbalances and insulin resistances (Ramey, 2011).  Laminitis is the swelling of the laminlar layers because they are unable to process or filter the blood quickly enough.  Laminitis is a strong prognosis, because it causes a weakening of the entire hoof capsule, as the various components are no longer strongly held together.  Laminitis often leads to founder, the rotation of the P3 bone which can be an extremely painful experience (Ramey, 2011).

The large plane of the bottom of the hoof capsule is the sole.  In a healthy foot, the sole should be a waxy texture and have a concave arch or cup like appearance to it (Romenako, 2017).  During locomotion the concavity allow the sole to drop and act as a suction cup to provide traction to the horse (Romenanko, 2017).  Many domestic horses suffer from a thin sole that easily bruises and can cause significant pain to the horse.

The bars of the hoof capsule are an extension of the hoof wall which curl in adjacent to the frog.  The bars visually extend along the outside of the hoof capsule, but also extend inward and are a support mechanism on the inside of the hoof capsule (Romenako, 2017).  The buttress is the heel location where the hoof wall curls and the bars begin.

The frog is the more sensitive structure on the horse’s hoof.  This triangular shaped, rubbery structure extends out of the heel bulbs and ends at an apex approximately in the middle of the hoof.  Directly above the frog, the internal structure of the digital cushion resides (Romenanko, 2017).

The heel bulbs are at the rear of the hoof, and should be slightly raised of the ground, the horse should land on the buttress of the heel, not the heel bulbs.  In contrast a donkey should land on the heel bulbs and not the buttress of the heel (Romenanko, 2017).

External Factors

There are a wide array of factors that can impact the hoof.  The first factor that impacts a horse is the environmental conditions in which they are expected to live and work.  The second being the shoeing or trimming methods that they are exposed to.

Environmental Conditions

            Environmental conditions to which the horse is exposed to are theorized to be critical to the hoof morphology.  However, due to the numerous unnatural conditions to which we expose domestic horses (ex. Stable, farrier, riding, etc.) it is difficult to assess environment as an independent factor in the morphology of the domestic hoof (Hapson, 2012).  This inability to isolate environment as a factor, leads many researchers to examine the conditions of wild horse hooves, in varying conditions to determine the role environmental conditions play.

One study Ramey (2011), examined the feet of two groups of wild horses.  Both groups of horses were tracked with GPS monitors and were determined to have reasonably similar behaviour patterns, but one group of horses was located in an area with soft wet footing and the other were located in hard, rocky terrain.

Another study of five wild populations of horses in Australia concurred that environment played a significant role in hoof morphology (Hapson, 2012).  In this study, the wild horses habitat ranged from wetland like environment to hard and rocky soil, as well as horses who’s territory encompassed both types of environments.

Hapson (2012) discovered that various terrain types had direct correlation with specific morphology markers, and the study by Ramey was in agreement with Hapson’s conclusion.  Toe length was a marker that changed significantly in the varying environments; the harder the ground the shorter the toe and shorter the break over distance (Hapson, 2012).  This is speculated to occur because in the hard footing, the hoof wall is subject to more abrasion.

A deeper more concave sole is present in horses living in soft footing and a more shallow and thick sole in harder footing.  This is speculated to occur because it is critical for horses in rocky terrain to have thick soles that will not become sore when they walk across rocky terrain for extended periods of time (Hapson, 2012).

Horses living in soft footing environments tended to have splayed feet with larger flares while horses in hard footing environments tended to have upright feet with minimal flaring (Hapson, 2012).   This is speculated to occur because a wide, flared foot will give a wild horse an advantage in wet footing.

Understanding how environmental conditions can impact the hoof is critical for owners of domestic horses, as the equine athlete is often expected to live in one environmental condition, but expected to work in another.  For example, it is common practice for horses to live in soft grassy pastures and rubber and straw lined stalls, then be taken to a sandy riding ring to compete.

Further, many domestic horses are forced to stay inside stalls (average at 10 feet by 12 feet) with minimal turn out or outdoor activity.  This can change how the hoof functions and how it processes blood, shifting the health of the hoof (Romenanko, 2017).  Horse owners also often shift the natural diet, encouraging the horse to eat high sugar, high fat and high protein concentrates with minimized hay and roughage consumption.  The change in diet can impact the health of the horn that is grown, and there for the health of the whole hoof capsule (Romenanko, 2017).

Shoes

Shoes and various farrier techniques have been a significant environmental factor in the development of hoof morphology.  However, the history and origins of the first horse shoe are long and complex, without being well documented.  A study by Roche (2008) complains that there is a “general lack of interest in which historians across Europe, have displayed for this [horse shoes] subject…”due to the fact that “in horse history there are two totally separate and mutually ignorant literatures.  One written by horse professionals and another by trained historians” (Roche, 2008).  The conflicting histories make the subject complex to understand, as the horse professionals often forget to report any significant social or cultural histories tied to the horse shoe and the historians often omit how the horse shoes may impact the horse (Roche, 2008).

A historic text written in 1859 by F.N.L. reports that the first written reference to horse shoes was in 1384 in Ireland.  The 1384 Irish text recounts that Doachain Tomaltagh MacDorey was murdered while he was shoeing his horse (F.N.L., 1859).  At this time Iron was of utmost value and was a rare commodity in Ireland and blacksmithing was likely limited only for the wealthy.  There was also a discovery of five ancient horse shoes in the area, reported by the 1384 text, however due to their condition they were unable to be dated (F.N.L., 1859).

Another historic text by Bates, written in 1902 recounts evidence of horse shoes found in Corneto, ancient Eturia, part of what is now Italy.  The shoes discovered in Corneto were four bronze shoes that could be dated back to about the fourth century B.C.  The shoes were in near perfect condition, as they were found buried in a tomb (Bates, 1902).  In the tomb the shoes were found near a skeleton that can be aged at about twelve years old, as well as the horse’s tack.  It is hypothesised that at this time it was common practice to slaughter a horse and bury it with its wealthy master (Bates, 1902).

The shoes found in this tomb have a slightly different style compared to modern day horse shoes.  These horse shoes have the same arched style, but from medial toe quarter to lateral toe quarter the shoe is considerably wider and is almost covering a quarter of the hoof’s solar surface (Bates, 1902).  The shoes had three large holes, compared to modern shoes that have six to eight small holes.  It is hypothesized that the horse would wear a snug leather boot, then the iron horse shoe would be strapped onto the hoof when the horse was in work (Bates, 1902).  It is interesting to note that the ancient style of horse shoeing recounted here does not include nailing into the hoof wall.  After thousands of years of accepting this practice, modern equestrian professionals are beginning to move away from nailed on shoes in the form of synthetic hoof boots and glue on shoes.

Another historic text by Fraser recounts the discovery of 19 horse shoes found in ancient ruins in a Mattium Strong hold, part of what is now Germany, which can be dated back to A.D. 15 (Fraser, 1934).  These roman horse shoes are much more similar to what is found in modern day farrier practice.  There are three nail holes on each side the horse shoe and appear to be for draught style horses.  These shoes are estimated to be from the third or fourth century (Fraser, 1934).

Although the exact origins of the horse shoe remain unclear both in location and time frame, it is clear that during the Middle Ages, the practice of shoeing a horse went from uncommon and an indication of status and slowly became more common place and used for merchants and some farmers (Roche, 2008).  As previously mentioned, it is difficult to decipher the impacts of the early horse shoe on the equine, as the histories are split and not well recorded.  However, in the late Middle Ages horses began being regularly kept in stalls, both in castles and in homesteads (Roche, 2008).  It was at this same time that shoes began being put on horses outside of the wealthiest classes.  Although it is not written in a text, when understanding how the hoof functions, it is a plausible jump to conclude that the increase in stalled horses made shoeing a necessity rather than a privilege.

Blood flow is critical to ensure a healthy hoof capsule as it is filled with live tissues and structures that will die off if blood flow is not maintained.  With minimal blood flow, the horn will grow weaker, the sole will become this and susceptible to injury as well as a plethora of other potential hoof problems including but not limited to soreness, misshaped heels and decreased strength of soft tissue (Ramey, 2011).  The issue of blood flow in related to a horse being kept in a stall because in a natural and healthy lifestyle a horse gets “a shot of blood with every step” (Ramey, 2011).  As the hoof capsule expands with impact on the ground, the capsule fills with blood, and as the hoof comes up and begins to contract again the blood is forced out of the capsule and back up the leg (Ramey, 2011).

This blood circulation is related to how the hoof provides shock absorption for the horse.  The high transient energy forces are dissipated with the hoof capsule, through the rapid movement and expansion of tubules and vascular channels in the hoof (Ramey, 2011).  This is called the hemodynamic flow hypothesis.  The hemodynamic flow hypothesis is based on the principles of biomechanical hydraulic fluid theory (Ramey, 2011).  In the simplest of words, the vascular channels fill with blood reducing impact on the bone structures.  When this function does not have the ability to work (when the horse does not move) it increases stress on the bones and decreases the overall health of the hoof capsule.

Without the ability to move, the blood flow significantly slows down.  The horse may experience stalking up, where the blood continues to fill the distal limb and hoof capsule, but the body is unable to push the blood up and out of the leg, greatly reducing circulation and the health of the hoof (Ramey, 2011).  Shoes were then seen as the solution to fix the hoof, as they bind the hoof together and allow the horse to continue working, even if it has a poor quality hoof.

Although there are many contradicting pieces of information about the benefits or harmfulness of shoes, the practice of horse shoeing persists.  I feel that minimal research has been conducted because of the horse shoe’s ability to keep a horse sound.  Although there are many potential health risks to shoes, they have an uncanny ability to hold a hoof together and allow a horse to continue work, even with a plethora of unsoundness.

There is also an idea that shoes can aid in making a horse faster and stronger in competition.  One barefoot trimmer recounts how he convinced the owner to take the race horse’s shoes off and go barefoot in a race.  After winning a significant race, the owner insisted that shoes go back on because the horse was running so well, and they will run even better with their shoes back on.  After the shoes were returned to the horse’s feet, the horse was a full second (or five horse lengths) slower than their previous winning race (White, 1998). Hopefully as more research is conducted on the anatomy and function of the distal limb, equestrian culture will shift to a future based in research and not tradition.

 

 

Work Cited

Bates, W. (1902). Etruscan Horseshoes from Corneto.  American Journal of Archaeology. 6(4).398-403.

Belknap, J. K. and Durham, A. E. (2017) Overview of Laminitis Prevention, in Equine Laminitis. John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9781119169239.ch47

Butcher, M., et al. (2007). Superficial digital flexor tendon lesions in racehorses as a sequela to muscle fatigue: A preliminary study. Equine veterinary journal. 39(6),540-545.

Cornelissen, B.P., Rijkenhuizen, A. B., Buma, P., Barneveld, A. (2002). A Study on the Pathogenesis of Equine Sesamoiditis: The Effects of Experimental Occlusion of the Sesamoidean Artery, Transboundary and emerging diseases. 49(5) 244–250.

Dyson, A., et al.  (2011). Anatomical, magnetic resonance imaging and histological findings in the accessory ligament of the deep digital flexor tendon of forelimbs in nonlame horses. Equine veterinary journal. 43(3) 309 – 316.

F.N.L. (1859). Ancient Horse Shoes. Ulster Journal of Archaeology, First Series. 7. 167-169.

Fisher, H. (1973). ‘He Swalloweth the Ground with Fierceness and Rage’: The Horse in the Central Sudan II. The Journal of African History.  14(3). 355-379.

Fraser, A. (1934). Recent Light on the Roman Horseshoe. Classical Association of the Middle West and South 29(9) 689-691.

Goulet, C., et al. (2015). Radiographic and anatomic characteristics of dorsal hoof wall layers in non – laminitic horses. Veterinary Radial Ultrasound. 56(6) 589 – 594.

Hapson, B., Laat, M., Mills, P., Pollitt, C. (2012). The feral horse foot. Part A: observational study of the effect of environment on the morphometrics of the feet of 100 Australian feral horses.  Australian Veterinary Journal. 91(1-2) 14–22.

Lewis, C., et al. (2014). Effect of season on travel patterns and hoof growth of domestic horses. Journal of equine veterinary science. 34, 918 – 922.

Ramey, P. Rehabilitation and Care of the Equine Foot. Lake mont, GA: Hoof Rehabilitation Pub.,Print.

Roche, D. (2008). Equestrian Culture in France from the Sixteenth to the Nineteenth Century. 113-145.

Romenanko, K. (2017). Natural barefoot trimming course.  Nature’s barefoot hoofcare guild.

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