• theequinedocumentalist

Horse Shoeing - How Much Length?

Updated: Mar 10, 2020

There is a long list of factors that influence the amount of length a farrier shoes a horse with, many are environmental; type of work, type of turnout and shoeing cycle, to mention a few. Even without these variables the ideal amount of length of shoe remains highly subjective, research into the different biomechanical effects of different lengths needs to be done to work toward a standardisation of the industry, however we can use some physical principles to help establish some ideals to work towards, understanding that these may still have to be compromised according to the environmental factors.

The hoof is a structure that responds to the biomechanical forces that act upon it following the laws of physics, therefore we can use maths and physical laws to help establish the ideals in shoeing that structure. When applying a shoe we are looking to create centralised load and biomechanical efficiency to preserve all biological structures, so shoeing around the centre of rotation (COR), in the authors opinion, has got to be the first step in establishing the correct length of shoe. We also have to appreciate that the front and hind hoof have different conformations and should be assessed differently for their appropriate shoe lengths.

This picture from Progressive equine ( https://www.facebook.com/hoofscanandhoofcarecentre/ ) raised this question online, suggesting that establishing heel length to correspond with the dorsal wall angle is possibly a viable protocol. The author suggests this is a method that deserves investigation.

The following principles are the authors protocols for establishing length, as stated previously the industry requires evidence-based research to validate shoeing length.

Shoeing around the COR goes some way to establishing the authors chosen shoe length.

Foot mapping helps to establish the COR with the absence of radiographs.

Trimming to the highest widest part of the frog helps to point at the appropriate length of shoe. This point is expressed by O’Grady (2019) as the point at which to ideally trim and could be our first potential for shoe length fit, a common protocol for many farriers would then be to shoe to the widest part of the frog, being slightly further back, so this is our second potential shoe length. The length can be worked out as a 50/50 split around the COR instead of to an external anatomical point, although some would argue that 50/50 is not practical in some circumstances it does remain, in the authors opinion, an ideal and is often achievable by shoe fit.

The length of shoe should help to establish the balance around the centre of rotation. Had this foot been in a toe clip with the same fit it would have remained at 45/55 which may be acceptable to some, or 50/50 could still be achieved with even more shoe length at the heels, essentially, in this context, shoe length depends on toe length and toe length depends on the length of lever arm from the COR. The author most often choses to come under the toe and add length at the heels in appropriate proportions to establish the 50/50. For further reading on shoeing around the COR https://www.theequinedocumentalist.com/post/hoof-balance-shoeing-around-the-cor-in-3-dimensions

Radiographic appearance of 50/50 split around the COR. The length of shoe (assuming appropriate toe length) establishes this dorso-palmer balance.

This is a fundamental basic of the authors establishment of shoe length but there are other factors and reinforcing principles. When establishing balance around the COR a centralised load is established because both halves of the foot have the same surface area and therefore pressure.

We can then look at this from a lateral view.

From a lateral view we can see where this length equates to in terms of the digit, before and after applying a larger shoe around the COR, the author would suggest that this is the basic minimum length of shoe fit (with environmental factors removed) with a foot with minimal distortion, one could argue this foot still looks like it could have more length, so how do we establish maximum length? When does length turn from support to leverage? Other factors begin to also come into play, what about when the bulbs are prolapsed? What about when the heels end forward of the highest widest part of the frog? Often these morphologies come hand in hand, we can use geometry to help re-establish reference points.

An important point to drive home is that trimming plays a huge role in creating optimal physical influences, the shoe should enhance this, trimming down the heels to the highest widest part of the foot is a good start. Often farriers are reluctant to lower heels too much, however often the heels that require lowering are of such a low angle that the gain in basal length far outweighs the drop in hoof angle, trigonometry can help to explain this.

This image shows how underrun heels can be taken down with a smaller effect on hoof angle compared with more upright heels this is relevant because “length” of shoe applied depends on how close to the heel length required the heels already are with the trim.

In physics the triangle is the strongest shape and O’Grady (2013) expressed how the ideal conformation of the digit should present with a triangle, Balchin (2017) also discussed the applications of Pythagoras in assessing hoof conformation in his assessment of the golden ratios in the hoof.

Balchin (2017) right angle triangle created in 59% of feet, feet outside of this range were thought to have been pathological in some way. This finding could point at another suggestion for shoe length, the golden ratio, the length of the shoe is divided by 5 to have the same figure as the dorsal wall divided by 3 and the hairline divided by 4 and creating a right angle triangle with the dorsal wall and hairline. However this could still be questioned when we have pathological feet not following the golden rule.

We can continue the use of triangles to create further perhaps more practical possibilities for ideal shoe length.

A plum line taken from the centre of the distal condyle of the 3rd metatarsal, which often follows the middle of the leg mass close to the back of the bone, creates a right angle triangle with a straight hoof pastern axis, where this lands at the ground could be an indicator of appropriate shoe length. Radiograph courtesy of Progressive Equine.

The author uses this geometrical indicator and has found that anecdotally it commonly correlates to shoe placement around the COR, which also commonly correlates with the widest part and base of the frog. However, again this is not always practical especially if the horse has particularly sloping pasterns but could point toward a possible ideal.

With prolapsed heels/bulbs often this point can still appear too short, the heels will be run forward of the widest part of the frog often with parts of the bulbs almost becoming weight bearing in extreme cases, the author will then often use a line dropped from the back of the bulb as an appropriate shoe length. This correlates with O’Grady (2018) which discussed the appropriate length of hind shoe.

Illustration of O’Grady (2018) and a common authors reference point for the fitting of hind shoes. Hind feet often have a shorter distance from the COR to the base of frog/end of heel, in order to still maintain COR balance they may require more apparent length then fronts. When there is substantial forward migration in a fore foot the same proportions can present, therefore they may require the same increase in length. This point often corresponds with the same line dropped from the distal condyle as in the fronts.