Farrier Takeaways

  • Farriers must be able to communicate with owners about toe length, particularly those who don’t understand negative consequences of excessive shortening.
  • Preserving sole depth is of the utmost importance in trimming the foot and in regard to toe length.

Which toe length do we talk about? What — there is more than one?

No doubt we all discuss toe length, but exactly what toe length do we mean? Most people will comment that feet are too long simply by looking at the dorsal aspect of the hoof.

There are actually three places to measure toe length; all are interconnected structurally and usually have minimums, which are required to have a hoof that is protective, mechanically optimum and strong. There are anatomical and mechanical strengths gained from that interconnection. A sacrifice of any one of those lengths will compromise the hoof and its function.

Three Measurements

The first measurement — the most visual and one frequently referred to by veterinarians and horse owners — is the dorsal wall toe length, measured along the dorsal wall. Often done by sight (the complaint would be that “it just looks long”), it is generally considered the shorter measurement would be the better. For some reason, the concept that a horse cannot move with any hoof length has become the leader of thought process in shoeing horses. That perception is so far from the truth that it bears no resemblance to a common-sense approach to having a mechanical length that is mechanically beneficial to the limb. In addition, that length contributes to maintaining mechanical strengths and protection to the coffin bone.

The second measurement is the length of foot horizontally (horizontal/longitudinal component) from the center of the foot to the toe of the hoof wall on the ground. That distance is the lever arm of the deep digital flexor tendon (DDFT). That lever arm length is the tool used to vary the mechanical timing of the hoof rollover so it doesn’t roll over before the knee opens. That distance should also vary in regard to the differing lengths of pastern conformation above the hoof.

Force application is provided by a stationary DDFT insertion and the toe of the hoof becomes the fulcrum for that lever. That distance from insertion to toe is varied by toe length and angle. That defined second-class lever also provides for a mechanical advantage to the force application by increasing the length of that lever arm. Couple that statement with the fact that all weight-bearing studies have shown that the weight centers move toward the heel during loading and mid-stance and to the toe before rollover. This shows that Mother Nature knows more about biomechanics than we do. You can measure this lever arm by placing a square at the base of the toe, with a leg of the square upright and measuring parallel to the ground to the coronary band. You also can measure it from the tip of the frog to the toe in non-displaced P3 digits.

The third measurement is the sole depth of P3 from the ground plane (which is included in total hoof vertical depth) and adequate cup to that sole. This is the most important length to consider. That sole depth and cup are required to maintain P3 protection from excessive internal movement and cushion from ground interaction during weight-bearing. An adequate sole cup provides support to the base of P3, yet allows depth for P3 normal displacement within the hoof capsule during weight-bearing. That protection resists crushing the vasculature suspended from the distal borders of P3, ensuring damage does not occur during normal movement. Lack of adequate sole depth makes sole or vascular compression a higher risk from the factors above. In addition, a strong cup under the toe of P3 supports the toe of the foot (and coffin bone) from excessive loads by the DDFT on the lamina. Without adequate dorsal wall length, you will have inadequate sole depth or cup.


That required dorsal toe length is arbitrary, but at a bare minimum it must be protective ...


Changing the Thought Process

None of this is new. Professor William Russell states in the introduction of his 7th edition of Scientific Horseshoeing, “The long-pastern horse needs to be shod in front and behind with long toes, while the short-pastern should be shod all around with short toes.” This practice makes the vertical depth the most important length to maintain and the horizontal relationship between toe length and pastern length.

We have all been there on the first one. Either a client or one of their intelligent friends has asked, “Why are those feet so long?” or “Don’t you know that long feet cause lameness?” You then have to come to the defense of the horse and try your best to inform them of the necessary length the hoof must be. Of course, you know full well that if you cut the bottom so short that the base is flat and the sole is soft, you will do more harm than good and will soon be out of that job. Clients have read more than one article on shoeing that harps on any toe length becoming problematic. Some horseshoeing schools have taught a “prescribed length” that those students should cut the hoof’s dorsal wall length to.

That required dorsal toe length is arbitrary, but at a bare minimum, it must be protective. Dorsal wall toe length varies due to the conformation of the limb (see note previously on Russell’s comments) and the horse’s work requirement (shoeing a Western pleasure horse is different than a five-gaited horse). Some medical or mechanical conditions may allow P3 to displace distally within the hoof capsule, making it “look longer than normal.” These feet can be easily cut shorter on the solar surface from that displacement. Considering that into the equation confuses many people so they just go back to the sight of the foot — “it looks long.”

Dorsal toe length also is coupled to the angle of the hoof and the horizontal (longitudinal) component (lever defined from the hoof center to the edge of the toe). Lowering the dorsal wall angle will increase the horizontal component while raising the hoof angle will shorten it. There are combinations of dorsal wall length and angle changes that will provide the same horizontal component, which means the DDFT application lever is the same. An example of that is raising the hoof angle (shortens the lever arm) and then lengthening the dorsal toe length proportionately so that the horizontal lever arm is the same as you started. Executing these changes with a mechanical goal in mind is a priority in performance horses. Making decisions like this for lame horses also is important if you are trying to reduce tension on damaged soft tissue or if one of the three lengths is markedly short and possibly a source of pain. Many of us were taught and became locked into believing that shorter is always better. We need to stop that thought process. We should instead consider what the horse needs mechanically and that required length for protection rather than the influence of “I don’t like the looks of that.”

The length of the second-class lever from a vertical line drawn from the center of rotation to the ground and then measured from that point cranially to the dorsal tip of the hoof wall. This measurement is the one that becomes the optimum measurement for balancing the fetlock horizontal mechanics with the hoof’s applied horizontal mechanics (again, reread Russell’s statement). You often see this out of equilibrium before you understand it. If you watch a horse work and see it slipping from the ground (for example a reining horse cantering with very slippery sliding plates on the back), you will see an application of force that is greater than the resistance required to maintain stability during ambulation. It is harder to see this on an average horse using our slow operating eyes. Slow-motion video has helped in ascertaining these subtle failures of application or weight-bearing. Shoe wear is another way to differentiate that failure from normal. Uneven toe wear (out of center or excessive means sagittal or horizontal plane misalignment) is an example and one branch worn differently than the other would be another (transverse plane). Information gathered in this manner is factual and needs to have factual application changes to address those problems.

It is the sole depth that is of primary importance to the horse. Normal proprioception of ground interaction by the base of the hoof is required for the horse to “feel” the ground correctly to accept load and apply force. I often teach that I can feel bubble gum on the bottom of my shoe and will eventually remove it because of that aggravation. No doubt a horse can feel those subtle differences as well. The normal hoof bears 60-78 psi on the base of the hoof so correct ground interaction is imperative for normal function. We bear about 7 psi on our feet and we complain about standing on concrete.

Those massive forces of weight-bearing are supported by external and internal strengths of the foot from anatomical connections and mechanical shapes. So 60-78 psi is a huge number to have to mediate during movement (and some movement increases those forces in the hoof by up to three times). So not only is the hoof used for force loading and application, it is a huge factor in protecting circulation and soft tissue within the confines of the wall. Lamina integrity is important to maintain attachment strength of P3 to the wall for transfer of DDFT forces to the wall. Frog weight-bearing is important to help hold up the bone column within the hoof. The conical shape of the wall (including the bars) and its structured arc supports add strength to help resist deforming forces applied during ambulation.


It is the sole depth that is of primary importance to the horse…


Sole cup, not just in front of the frog but through the base of the hoof, is extremely important in augmenting strength supplied to the terminal lamina. That cup allows the similarly cupped P3 to remain more stable and limits the coffin bone’s movement during weight-bearing. Excessive P3 movement could potentially compromise circulation suspended from its distal border and excessive stretching or tearing of the terminal lamina. It has been reported that a minimum depth of sole would be about 15 mm of depth on the average horse. That might be acceptable in some cases, but a more conservative approach (say 20 mm or more) would offer the horse with any solar problems (bruising, abscesses or P3 border damage, for example) more protection from ground interaction.

How do you gauge that while shoeing a horse? Good question. We do not always have the luxury of radiographs to confirm the amount of sole depth on the horse standing before us, we can still do something positive to restore or maintain adequate sole depth. First, do not cut the wall straight out of the box. Simply take your knife and just clean a layer of the sole so that you are visually inspecting while palpating for soft areas or any visible (bruising or serum history) information that sole compression is occurring. Look for stretched and discolored (red or yellow indicating blood or serum) lamina in any area of the hoof indicating excessive tearing, shearing or compression forces. Lay a ruler from medial to lateral just in front of the frog so that you can measure that depth to the sole. If you consider that the physical sole depth at the tip of the frog is approximately 5 mm, then that measurement to the ruler should be at a minimum of 10 mm (approximately a ½ in.), but in actuality should be closer to 15 mm.

Now use your knife to cut a sole cup that is uniform and the sole remains the same thickness throughout (assess that by palpation with your thumb and fingers) and clear out to the white line circuitous the hoof wall. Don’t get busy cutting the frog either, as its relationship to the center of the foot allows it to be a major player in support to the bone column and sole cup by decreasing internal forces of weight bearing being transferred to anatomical connections. Overworking those anatomical connections tortures the anatomy so that eventual failure may occur (like lamina fatigue and damage or sole bruising). Cut the wall length to the limit created by the cup defined by the sole edge at the lamina and don’t cut the cup flat anywhere. The deeper and more uniform the cup, the more strength it has. If you want a deeper cup, then just allow some wall length to remain so you can create a deeper and stronger cup.

LEARN MORE

Read other essays by Randy Luikart that may lead you to rethink commonly held hoof-care beliefs among farriers at
AmericanFarriers.com/0521

These three lengths of toe are important in their own right, both for hoof health and meeting the specific mechanical ambulatory needs and performance requirements for the various conformations above that hoof. Each measurement contributes its functional merits and minimums to the horse during ambulation. Prudent farriers will prioritize these lengths by the obvious necessity to maintain the vertical depth of P3 from the ground for soundness issues. The other two function to establish some linear relationships to distal limb joint equilibrium on the longitudinal (sagittal) plane during ambulation. How farriers gather that information and apply it to the conformation they are working with is most certainly dependent on their training and knowledge of that application.

Far too many times we just hear, “It just doesn’t look right,” and “Can you shorten that toe?”


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