A New Angle on Hoof Wall Growth
Hoof wall growth - a simple function of the equine foot; or is it? We have been taught that the hoof takes about twelve months to grow from hairline to ground, that growth averages about 1/4 inch per month. This statement would qualify the common belief that hoof wall growth originates at the coronary band. I would like to take this opportunity to offer an alternative hypothesis. When I began to remove horseshoes and transition horses to barefoot, some five years ago, I began to notice a number of changes occurring that somehow challenged the accepted beliefs of how the hoof grows.
Most obvious to all involved was an increase in the growth rate of horn. The growth that was observed, however, was not so predominant at the coronary band where you would expect, but rather in wall thickness. If we are to accept the theory that the largest percentage of hoof growth occurs at the coronary band then this new growth should not have been possible at the distal end of the hoof capsule. But there it was, in the wall, sole, bars and frog. Wall thickness increased dramatically in as little as twelve weeks. Bars grew back down in far less time.
A number of questions began to develop. Was this truly new growth? What caused it, if it were? Was it simply a matter of increased circulation? What was the stimulus for this new growth? And most importantly, a very basic question that has not been clearly answered, in my opinion, how was the hoof wall growing?
I have made a number of observations in the barefoot hoof trimmed with the HPT Method (High Performance Trim). As stated, increased thickness of the wall became apparent. Secondly a diminishing of stress lines or growth lines just below the coronary band has been documented.
A visit with Dr. Robert Bowker, VMD, PhD at Michigan State University offered insight as to what may have been taking place in the newly de-shod hoof. In our discussions on hoof growth Dr. Bowker theorized that the increased growth being observed was being produced at the secondary laminae in direct response to stimuli. Simply put, this new growth was coming from the inside out. The question now became what were the stimuli? And was this new growth going to be beneficial to the barefoot horse? As I looked closer at this new growth it became clear that it was in fact coming from the inside out and not from the hairline - no huge surprise. Considering my belief that Structure + Function = Performance, it should follow that this increase in wall thickness would be of benefit to the hoof, but you must take into consideration that in the HPT Method hoof wall is not a major weight bearing component. It is however a major component in shock absorbency providing resistance. Now it was becoming increasingly apparent that the wall is much more complex and does play a huge role in managing shock, just not how we believed it to be.
In my teaching of the HPT Method students often mistook what I will label as the "inner wall" for the white line. What my students were observing was the area of hoof wall adjacent to and outside of the white line (stratum internum). Was this area of hoof wall the same as the outer wall with moisture content being the only difference? It is believed by most experts that the innermost wall contains a higher percentage of moisture than the outer portion of wall and I do agree with this. It is this moisture in part that allows the inner wall to deform and absorb concussion that the outer wall is not meant to take. That's correct; I did say that the outer wall was not meant to take concussion. I propose that the hoof wall is far more complex than previously considered and that the outer wall and inner wall are distinctly different with the growth for each originating from two opposing, very definable areas.
First let's take a look at how we believe the hoof wall grows. In most modern texts on hoof wall growth it is stated that the hoof wall grows from coronary band originating at the papillae. In a recently released textbook by Dr. Hiltrud Strasser, "Hoofcare Specialist's Handbook: Hoof Orthopedics and Holistic Lameness Rehabilitation", this description of hoof wall growth was given: "the papillae produce around themselves very hard horn in a spiral shape. Between the papillae, soft and sticky horn is formed, which glues together the hard spiral horn tubules, resulting in the hoof. The constant horn production at the coronary band bulge causes the hoof wall to grow down toward the ground." (Strasser and Kells, 2001)
I found an interesting note in "Horse Anatomy" (R. Kainer & T. McCracken, 1994) that I believe is very relevant to this discussion: 'hoof' and 'foot' are not the same. In short, the hoof (like your fingernail) is a highly cornified (horny) epidermal structure lacking in blood vessels and nerves. The foot includes the hoof and underlying corium (dermis) and all structures including and distal to the coronary band.
In Dr. Doug Butler's book, "The Principles
of Horseshoeing II" the author states that the hoof is designed
to bear weight. The hoof tubules have a spiral columnar structure
that makes them resist compression and flexion. More significantly,
he states that the laminar attachment of hoof to bone suspends the
skeleton and weight of the body from the hoof wall. (This union
viewed at the sole is seen as the white line.)
Butler further explains that the laminae redirect the forces acting on them and dissipate the concussion coming up from the ground and down from the body. The primary and secondary laminae increase the surface area for dissipating concussion as much as 30 times.
My question is this: how does the hoof wall move downward along the laminae attachment and still provide for weight bearing and structural stability? Is it simply a matter of providing surface area? I don't believe it is and offer the following hypothesis based on my observations.
As I stated earlier I was observing new growth in the feet of the horses where shoes had been removed. Upon closer examination it appeared that the growth was in actuality an increase in mass and density. In the study of cadaver hooves and live horses both shod and unshod, there was evidence that the inner wall of the shod hoof was very different from that of the barefoot hoof. In the shod hoof the inner wall tends to be thickest at the toe, while very thin through the quarter and the heel area. In contrast the hoof that had been shoeless for more than three months had an inner wall that appeared more consistent in its thickness from toe to heel. Was this just a matter of moisture content and increased circulation, or as of yet some other unknown factors? Another bit of evidence presented itself over time that I think provides crucial evidence supporting my hypothesis. Over time the horses that have had the HPT Method applied showed fewer growth or stress rings distal to the coronary band.
When I looked closely at how the HPT (High Performance Trim) is applied to the wall of the foot it was clear that the outer wall was non-weight bearing. In the HPT the outer wall is beveled away from the white line relieving the outermost surface area of the wall from concussion. The inner wall shares the responsibility of weight bearing and concussion with the sole.
My hypothesis is that growth of the wall is two-part and the growth in the outer wall is separate to that of the inner wall. It is theorized by Dr. Bowker that cells responsible for forming tubules of the wall form at the secondary laminae (epidermal laminae) throughout the laminar corium and produce tubules of varying lengths and girth in response to given stimuli. I hypothesize further that the secondary laminae's primary function is the production of the tubules responsible for the inner wall and that the tubules produced here differ from those produced by the papillae of the coronary corium. How they differ will require further study; however my observations in the field may help us to better understand their independent functions.
Based upon observing the apparent effect of unloading the outer wall, it would seem logical, due to the density and rigidity of the outer wall, that it be best suited for the prevention of abrasion and not as a means by which to absorb concussion. In traditional shoeing it is recommended and deemed correct to load the entire wall, though in my observations of the shod hoof there is a higher percentage of the appearance of growth rings than on that of the unshod hoof. I believe that the tubules of the outer wall do originate at, and are produced by, the papillae of the coronary corium and grow from there to the ground. The outer wall tubules provide a means to protect the inner wall and its tubules from the elements and the function of the inner wall is to absorb concussion. The growth of the inner wall, being always in motion both laterally and distally, and the tubules being of varied length and girth would produce a wall that is made up of hundreds - perhaps thousands - of independent tubules, each allowing for distortion and shock absorption. Due to its higher moisture content and perhaps even unique keratin base, the tubules of the inner wall are pushed about in response to various stimuli (pressure, shock). The length and girth of the tubule would also be determined by this stimulus.
Here is how I hypothesize hoof growth: In response to stimuli (pressure, shock) the capillaries of the secondary laminae provide cells that form into tubules, with the orientation of these tubules running vertical to the laminae corium and with the length and girth of the tubule being determined by stimulus. The tubules that make up the inner wall are always in motion being pushed outward and downward by the production of new tubules behind and above the previous. The outer wall growing from the coronary band down moves over the inner wall providing protection. It is the stacking of tubules of the inner wall and their softer consistency that provides for the absorption of concussion. Think of the inner wall as a lava flow and the outer wall as the top crust that moves along with it. Though there are differences, you should get the idea. When the stimuli are correct the growth of the two walls is in equilibrium and each functions correctly, with the outer wall providing protection to the inner wall and the inner wall absorbing concussion and providing adequate structure. This hypothesis would explain how the bone column can be suspended from the laminar corium and still maintain stability. The number of laminae increase in response to stimulus, providing additional production of tubules in the inner wall where needed, with stimulus being dictated by a simple trim or the application of a shoe.
Think of the ramifications if this hypothesis
is proven out. It would show that in our attempts to soften the
outer wall with hoof dressings we were actually compensating for
a diminishing inner wall (due to incorrect stimuli) by having the
outer wall do the job of the inner wall, absorbing concussion. It
would also point to the fact that how the horse is shod is incorrect,
that the growth rings could be a direct result of loading the outer
It never ceases to amaze, how nature seems to provide the evidence only to have man ignore it.
© 2002 KC La Pierre, RJF, EP
About the author:
Keith "KC" La Pierre, a horseman for over two decades, a graduate of the Brewer School of Harness Racing, and holder of a USTA trainers license in the early 80's, became a professional farrier after becoming dissatisfied with the work being performed on his own horses. KC has been a professional farrier for almost 18 years, certified with the AFA since 1989, passing their Journeyman written exam in 1990, and he recently has become a Registered Journeyman Farrier and member of the Guild of Professional Farriers.
After working 11 years at doing it traditionally, KC realized something was missing and thought that by increasing his forging skills he would be able to produce therapeutic and finely crafted hand-made shoes that would help him to rehabilitate the deformed hoof and help the lame horse. To this end, in 1994 he began an apprenticeship as a Traditional Blacksmith at the Farmer's Museum in Cooperstown, NY under the guidance of Master Blacksmith Paul Spaulding. After completing a two-year apprenticeship, KC became a Traditional Journeyman Blacksmith. Armed with his improved forging skills KC began applying hand-made shoes of all types, only to come to the conclusion that the shoe was not the answer. Through the teachings of the Master Smith, KC had learned to break things down to the simplest denominator and determine how things worked before forging them. It was this mindset that allowed KC to look closely at the hoof and determine that the answers were to be found on the inside.
The results: The HPT Method and Barefoot Equine Podiatry. KC has lectured and demonstrated at numerous events including Equitana USA, PA Horse Expo and the TN Volunteer Horse Fair. He is currently traveling the US providing educational workshops and clinics to interested horse owners, farriers and veterinarians. The HPT Method has been displayed at the 2002 American Farrier's Association Conference and at Tufts University Symposium, "Hoof Care for the New Millennium". Additional information on the HPT Method has recently been published in the May/June issue of the "American Farrier's Journal". For more information, contact KC at 508-248-4444 or visit www.thenaturalequine.com.