Mitch L. Taylor, CJF

The role of a properly trained farrier is very important in the life of our equine companions. The performance level of a horse has a direct correlation to the skill requirements of the farrier. For example, a pasture animal living in a large arid environment will tend to need less frequent foot care. This animal can be maintained by a farrier with a lower skill level than an athlete that is stalled and used hard.

 

Mitch Taylor

Mitch Taylor, was born in Denver, Colorado.  He has been a professional farrier since 1975 and has been an AFA Certified Journeyman Farrier since 1982.  After receiving his primary farrier training at Colorado Mountain College, Mitch served his apprenticeship in southern California specializing in jumping and dressage horses.

Mitch received his bachelors’ degree in Biology and Chemistry from western State College of Colorado in 1983 and did his post graduate work in Equine Physiology at the University of Kentucky. As a graduate student at UK, Mitch worked as an assistant to Dr. James Rooney, the former director of the Maxwell Gluck Equine Research Center and a noted authority on equine anatomy and Biomechanics.  Under Dr. Rooney’s tutelage, Mitch performed many case studies of the equine leg and hoof in order to further his understanding of hoof and leg biomechanics and lameness.

Currently, Mitch is the director of the Kentucky Horseshoieng School in Mt. Eden, KY.  He is an avid national and international farrier, competitor and currently works worldwide as a noted clinician in the field of equine limb anatomy and biomechanics.  Mitch continues to pursue his interest in equine research by continually investigating equine biomechanics and how that is affected through various shoeing modalities.    Working with his students at the Kentucky Horseshoeing School and through his private work, Mitch is able to continue his interest in the area of promoting sound farrier principles to all horses.

Why is it so important to have a properly trained farrier for the equine athlete? It all revolves around achieving and maintaining “balance”. The term balance in farriery is a complex idea that might best be described as the efficient use, storage, and return of energy in the horse’s foot.


Farriery is often referred to as “the master’s craft”; a trade that takes years to become proficient at and requires achieving a level of competency in numerous areas. Correct farriery is much more than removing excess horn and tacking on a shoe. Farriers can be thought of as the mechanics of the team that manage an athlete. We must have an above- average working knowledge of horsemanship, service industry business skills, and the physiology of the musculoskeletal system; including bone growth and development, gaits, locomotion, conformation, pathology of the limb, and metallurgy. In addition, farriers must attain expert skills on lower limb anatomy, biomechanics and hoof dynamics, foot trimming, shoe building, fitting, and nailing. On average, it takes about 3-5 years of training to become competent in these areas.

Limb Design: Over time, the horse has evolved as a cursorial? animal with exceptional athletic qualities that can attain relatively fast speeds (40+ mph) for short distances and can maintain a moderate rate of speed for long distances. The limb and foot are uniquely designed to facilitate efficient locomotion, to maximize speed and endurance and to dissipate the concussion of ground impact.

When compared to humans (whose limb orientation to the ground, is referred to as “plantigrade”), horses (who are considered “unguligrade”) carry on average 6 times the weight and have 5 times less surface area of the foot to carry load than we do. In other words, horses have a 10:1 body weight to surface area ratio, compared to humans who have a 2:1 ratio. In addition, horses reach speeds twice that of humans and can maintain that speed for 15 times longer. In short, the horse is a much heavier and faster animal that generates tremendous amounts of concussion on feet that have much less area to support weight and dissipate shock than humans. The specialized biomechanical adaptations of the lower limb, in particular the foot, are designed to respond to these forces in a most automated way. That is why the horse’s lower leg and foot is generally thought of as a wonder of nature.

In order for the equine limb and foot to maintain soundness it must function as it was designed. In order for us to maintain that function we must first have an idea of the horse’s general anatomy. There are no muscles in the lower leg of a horse to aid in support of the bone column or to aid in venous blood return to the heart. Therefore, it is critical to trim the bottom of the foot perpendicular to the long axis of the bone column so that the joint surfaces are congruent when viewed from the front or back. When one trims the feet to this standard the foot will be positioned under the center line of the leg.

Anatomy of the Distal Limb
The Foot: Few species of large herbivores demonstrate the degree of anatomical specialization of the foot that the horse does. For every ‘insensitive’ structure of the hoof there is a ‘sensitive’ counterpart. These sensitive structures nourish the insensitive structures (horny structures) which allows them to grow. Any injury, deformity or deficiency of these sensitive structures will have a direct effect on their insensitive counterpart.

The inner sensitive structures are unique as well, with the digital cushion, ungular cartilages, laminae and venous blood plexi being prominent and ideally suited to yield under load, dissipate energy and return to its original shape.

Hoof wall grows from the coronary band via the arterial blood supply from the coronary plexus. Normal growth rates are about ¼ inch per month, but can vary depending on time of year, age and exercise regime of the horse. The insensitive sole grows from the sensitive sole situated on bottom of the coffin bone and derives its arterial blood supply from the circumflex artery. This artery courses around the solar margin of the coffin bone which can be compromised by flat soled feet, sole pressure from shoes, and over pairing of the horny sole.

The external parts of the foot (wall, sole, frog, bars and white line) must be trimmed and maintained in a balanced state in order for the foot to function properly. There are four main functions of the foot:
To bear weight while standing and at speed;
To dissipate shock;
To aid in venous blood return; and
To give traction to the animal.

Bones of the Leg: Over time some bones of the limb have reorganized and adapted to facilitate efficient locomotion. The cannon bones and phalanges have elongated to provide a greater lever for propulsion. The sesamoid bones have become more prominent in order to increase the mechanical advantage of the suspensory apparatus. Some bones have reduced their mass in order to minimize weight. The splint bones are a good example of this adaptation. More weight means more energy needed to move them. The coffin (P3) bone is probably the most unique or specialized bone of the limb. A highly porous bone that weighs 2.5-3 oz. on average and is covered in dermis, commonly referred to as the sensitive laminae and sensitive sole. P3 houses the terminal arch and radial arteries that perfuse the sensitive laminae on its parietal surface. The solar surface of the coffin bone anchors the sensitive sole from which the horny sole is produced. Its articular surface which communicates with the short pastern bone makes up the floor of the coffin joint. The coffin bone is the only bone of the limb that is not encased by periosteum but by coriums, i.e., sensitive laminae and sensitive sole. The coffin bone is very susceptible to remodeling when not adequately protected.

Hoof Capsule Characteristics
Shape: The overall shape of the hoof capsule is wider at its base; facilitating a strong exterior architecture well suited for bearing weight. The horn of the wall and sole are thick and dense and the frog is well defined, taking up about 1/3 of the bottom area of the foot. The bars are a continuation of the wall and white line, whose function is to give stability and structural integrity to the back half of the foot.

Form: Because form follows function, front and hind feet have different shapes. The better shaped or symmetrical the foot, the better it functions. However, healthy feet are not totally symmetrical because of the different weight bearing requirements of different parts of the hoof wall. Most feet will have a distinct medial and lateral side, with the lateral side being more rounded and the medial wall being more upright. Front feet are generally larger and rounder with less concavity to the soles when compared to hind feet. Additionally, the dorsal, medial, and lateral walls have a lesser angle in front feet than those in the hinds.

There are three biomechanical characteristics of the hoof capsule:
It is constantly growing;
It is elastic and dynamic; and
It changes shape according to how it bears weight.

The hoof wall, white line and sometimes the frog are the main weight bearing structures of the capsule. The sole and bars bear weight intermittently. In order for the capsule to function well as a whole, all of the individual hoof capsule structures must be healthy. The hoof wall of a normal sized horse should be approximately 3/8 inch thick and should be straight with no flairs from the coronary band to the ground.

The sole should be about the same thickness, be concave, and tightly connected to the wall via the white line. There should be minimal wall separations between the sole and wall. The sole, having concavity to it, functions as a secondary weight bearing structure similar to an arched doorway. The thicker the sole the better it can give structural integrity to the capsule and protect the coffin bone from contacting the ground, conversely, the flatter the sole the thinner it usually is and the less protection it gives the solar aspect of the coffin bone.

An important element of farriery is how farriers can in influence the health and integrity of the hoof. By understanding anatomy and foot dynamics farriers can help to control growth and build strong feet. A lack of understanding of these elements commonly results in farriers that over trim feet and put them into a constant state of mechanical stress and compromised blood perfusion, which effects growth rates and quality of horn.

The Suspensory Apparatus
Since there are no true muscles in the distal limb, there must be a mechanism in place to keep the fetlock from slamming into the ground and to lift the loaded fetlock joint from its position at midstance, to a position that will allow the foot to breakover. This is accomplished very economically by storing and releasing the elastic energy stored within the suspensory apparatus; much the same way a rubber band stores and releases energy.

The suspensory apparatus is a term that describes the mechanism of support and function of the fetlock and coffin joints of the leg during the static and dynamic loading phases of the stride. It is the combination of sesamoid bones, tendons and ligaments that work in concert to support the fetlock in a manner which minimizes muscular involvement. This system of levers, pulleys and fulcrums serves to maintain the fetlock, pastern, and coffin joint in its normal position when standing. It also serves to resist over dorsiflexion of the fetlock and hyper flexion of the coffin joint under load. The suspensory apparatus has three main functions:
Support;
Shock absorption; and
Impulsion.

The anatomical structures involved in the suspensory apparatus are:
The main body of the suspensory ligament;
The medial and lateral extensor branches of the suspensory ligament;
The superior and inferior check ligaments of the digital flexor tendons;
The superficial and middle sesamoidian ligaments; and
The superficial and deep flexor tendons.

Additionally, the sesamoid and navicular bones are critical to the system by providing significant mechanical advantage to the tendons and ligaments.

The Mechanics of Locomotion
Phases of the stride: There are five main phases of the stride in any gait of the horse. Although the timing and animation of the individual phases change with speed and gait, these five elements make-up every stride from a walk to a full on run:
Heel strike
Slide phase
Loading Phase
Breakover
Swing phase

A highly organized sequence of events must transpire with every stride in order for the animal to travel clean and maintain soundness. When the foot breaks over, its toe and begins to protract the limb forward during the swing phase, there is an increase in velocity of the limb in order to catch up with the body. At the end of this phase the leg is straight and centrifugal forces have caused the joints to be open, or to have space between the bones within the joint. Hitting the ground at this moment would result in an increase in joint concussion and injury. Therefore the muscles of the forearm contract and actively pull or retract the limb toward the ground. Two things occur during this moment in time; the velocity of the limb and foot is slowed down thereby reducing ground impact forces, and, the joint spaces are brought together into what is referred to as the close packed position which helps to minimize joint cartilage injury. Any change in these sequences exponentially increases the chances of limb interference or musculoskeletal breakdown.

Principles of Correct Farriery for the Healthy Limb and Foot
Hopefully, the at this point reader has a better idea of how complex the functional anatomy of the equine distal limb is, and how important competent hoof care is to the health and longevity of the equine athlete. It is the horse owners responsibility to breed or buy animals that are sound, have adequate limb and foot conformation and to train the animals to stand for the farrier. It is the farrier’s responsibility to become adequately trained and to provide reliable service to the horse and owner. A good general rule in hiring a farrier is that you generally get what you pay for.

Handling Feet and Legs:
Position yourself as close to the animal as possible and make sure he is squared up
Ask for the foot by using universal queues and try not to “take the foot”
Always handle the leg by holding on to the foot from the bottom, not the leg or pastern
Note any pre-existing lameness

Evaluation of Foot Balance
Because the hoof is constantly growing, the foot and limb become progressively more out of balance throughout the shoeing cycle. Hopefully, your shoeing schedule takes this into consideration with the usual shoeing cycle being between 4-6 weeks. It is very difficult to accurately assess a shoeing job at the end of the cycle.

There may be a time in which you have a need to evaluate some basic parameters of hoof balance. Farriers evaluate the foot using four basic planes; mediolateral and toe to heel balance planes are viewed from the bottom of the foot. The two hoof pastern axis planes are viewed from the side and the front or back when the limbs are evenly loaded. CAUTION the ability of one to accurately see and relate this information to any conformation fault or pre-existing conditions takes years to develop.

Sighting Feet for Mediolateral Balance: Assessing mediolateral balance gives us the ability to objectively see if the bottom plane of the foot is parallel to the joints of the leg and if the bone column is perpendicular to the ground surface of the foot. Position the leg directly under the body while flexed. The leg should hang freely while being held with an open hand in front of the fetlock. Your head should be under or next to the body. Hind legs should hang freely while sighting down the point of the hock and plantar aspect of the cannon bone, pastern and foot.

Sighting Feet for Toe to Heel Balance: The healthy foot should have certain spatial ratios that if achieved, promote strength and minimize tension and compressions within the foot, or in other words, are balanced. When viewing the foot from the bottom, the length from toe to heel should be equally bisected by an area in the front 1/3 of the trimmed frog. The widest part of the foot at the quarters should also align with this landmark. Usually, the heels will be trimmed to the widest part of the frog.

Sighting Feet to Access the Hoof Pastern Axis: Viewing the foot by squatting down in front of and behind the legs gives one a good look at the dorsopalmar/plantar (front and rear views) hoof pastern axis. When viewing from the front, the cannon bone should be positioned centrally above the hoof and perpendicular to the ground. The coronary band should be parallel with the ground and the inside and outside hoof walls should be straight and of similar distance from the midline of the foot and leg. When viewing from behind, you should see a similar hoof, cannon bone alignment and the bulbs of the heels should be of equal distance from the ground.

To get a good look at the lateral view of the hoof pastern axis simply squat down beside the leg and see if the front of the hoof wall is parallel to the pastern. You will also be looking at the other leg to confirm that it has a similar alignment. From this view, a plumb line dropped from the front face or mid-line of the cannon bone should bisect the heels. Again, there should be no dishes in the wall of the toe, and the heels should be straight and approximately parallel with the dorsal wall at the toe. The coronary band should have a gradual slope from the toes to the heels.

Criteria for Shoeing
Not all horses need to, or should be shod. Barefoot horses can manage to balance themselves given enough space to live in. Once we take on the responsibility to shoe a horse we need to understand the possible negative consequences as well as the potential benefits. Unlike barefoot horses, the foot with a shoe on is forced to walk and perform on the planes we trimmed it to. If we did a poor job of balancing the foot, the joints and hoof structures are not able to function optimally and we could contribute to early lameness. If we did a good job, we have minimal impact on these structures. Nailing shoes on a foot is referred to as a necessary evil, meaning that it does impact the structures in a negative way but, the alternative is worse. Nailing shoes on limits the normal expansion and contraction of the rear half of the foot and although they do elevate the sole off the ground, they make it harder for the frog to maintain healthy contact on hard ground. When needed, the benefits of shoes far outweigh their negatives if done correctly. When done incorrectly, however, it sometimes would have been best to let him fend for himself.

We shoe horses for a variety of reasons but most commonly because the rate of wear is greater than the rate of growth resulting in a sore foot. Therefore, horses wear shoes for protection, not unlike humans. We shoe feet to support the capsule. A rigid shoe will yield support for the working animal like a steel shank helps the working man get through the day. We shoe horses to increase and sometimes decrease traction, depending on the discipline and terrain. Also, we shoe horses for therapeutic and (or) gait alteration reasons.

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