An overview on affected tissues and movement implications of horseshoes.
Shoes dramatically alter biomechanics.
Along with causing other physical issues in the body of the horse, shoes are most commonly seen to increase load to soft tissues during movement which alters biomechanics.
Three videos showing barefoot, plastic, and iron shoes at a canter in slow motion (4 frame/ps). In watching each video very closely, one may start to appreciate the severe increase in tensile loads to the flexor tendons with the implement of shoes. Keeping in mind there are also increased ground reaction forces running through the axis of each of the bones and joints. Looking specifically at the fetlock and pastern joints illuminates the degree to which these joints are being pushed out of safe ranges of motion.
Original footage retrieved from Eylon Joseph in 2019 https://www.facebook.com/100008094679070/videos/2445932172353248/
Repetitive strain is one of the most common risk factors for injury and promotes the perfect conditions for pathologies such as early onset arthritis, flexor tendon tearing, suspensory ligament damage and many more orthopaedic dysfunctions.
Beyond biomechanical stress, shoes also inhibit blood flow in and out of the hoof, increase ground reaction forces, contribute to peripheral loading, and disrupt communication between proprioceptors and the spinal cord.
How Is Blood Flow Affected?
The hoof contains a structural component known as the "frog", which covers the deeper structure of the hoof known as the digital cushion, a vessel-filled tissue. When the horse places weight on a leg, the ground pushes upward on the frog, compressing it and the underlying digital cushion (Kauffmann & Cline, 2018). This results in squeezing blood out of the digital cushion, which then helps to pump it back up the leg, helping the heart to work against gravity and allowing for used blood (de-oxygenated) to make its way out of the hoof (Kauffmann & Cline, 2018). Shoes inhibit the frog’s natural pumping mechanism by blocking their contact with the ground (Kauffmann & Cline, 2018). This not only leaves CO2 rich blood pooling in the limb but also contributes to atrophy in the structures of the foot. All structures in the body require adequate blood flow in and out to maintain function and vitality.
https://pixels.com/featured/horse-hoof-blood-vessels-christoph-von-horst.html
Why Are Proprioceptors Important?
In the human foot there are over 7000 receptors on the sole and heel. Similarly in horses we can see the majority of receptors being found at or near the heel (Bowker et al., 2010). Proprioceptors serve to tell the horse where their limb is in space and provide important sensory feedback on touch, pressure, and vibration (Bowker et al., 2010). Their main role is to detect stretching and movement of the muscles, tendons, and joints and relay this message to the spinal cord which then travels up to the brain (Budras, 2009).
Shoes remove the ability of these surfaces to contact the ground which reduces their ability to relay messages. The result is uncoordinated movement in limbs and difficulty feeling the feet. Over time, much like humans, neurons lacking stimulation atrophy which leads to further sensory deficits.
In light of the video shared with this, it would be negligent to leave ground forces out of this discussion. Shoes amplify ground forces by causing peripheral loading and increased ground reaction forces running up the joints of the horse.
How Do Ground Reaction Forces Play a Role?
According to Newton's third law the so-called ground reaction force (GRF) is the force exerted by the ground on a body in contact with it. When a body is just standing, the GRF corresponds with the person’s weight (Kent, 1994). When the body is moving, the GRF increases due to acceleration forces (Kent, 1994). For example, while running [trotting in horses], the GRF increases to up to two or three times the body weight (Kent, 1994).
Now add the weight of a rider and an immovable piece of steel and consider the subsequent increase in ground reaction force (GRF) and consider the ability for the foot to:
Feel the ground and receive sensory information
Effectively pump blood out
Mold and contour to various surfaces (joints above have to work extra hard to compensate for lack of slide and glide at the digital cushions)
Expand and retract to manage ground forces
The result, force running straight up the limb rather than being dissipated throughout the intended structures in the foot (Kauffmann & Cline, 2018). From my perspective, this can cause additional strain to musculotendinous units and joints up the entire leg into the shoulder further altering biomechanics especially at the high speeds seen in most performance horses.
What is Peripheral Loading?
Peripheral loading occurs when the hoof wall is so long that the frog, bars and sole are not touching the ground (Kauffmann & Cline, 2018). Often this dysfunction goes unrecognised but is a serious issue which can cause significant damage to the hoof over time (Kauffmann & Cline, 2018). This puts extreme stress on the wall and exposes the vital laminae to forces for which they are not designed (Kauffmann & Cline, 2018). This creates inflammation and disrupts proper blood flow in and out of the foot which can be very painful.
Image taken from the Essential Hoof Book, Kauffmann and Cline (2018)
Final Thoughts
The areas of concern noted in this post are limited to the limbs of the horse but there are multiple other structures up the chain that will be affected with altered biomechanics. Loading patterns to spinal segments are compromised and alignment issues may become very apparent which is why it is always important to take a whole horse approach when assessing the horse. A problem with hoof and limb biomechanics may present as pain and dysfunction in areas seemingly distant to the cause.
Moreover, in an article written by the Equine Documentalist, “Malone and Davies (2019), Clayton (2011) and Proske et al (2017), all found improved hoof morphology in the barefoot out of shoes” providing further evidence of more recent research in the field.
Now of course, there are situations when shoes are indicated. If this is the case for your horse, it is strongly recommended to provide breaks in shoeing cycles systematically. Many competitive horses are seen to go barefoot through the off season in order to allow these structures rest and recovery. In the case of severe or acute injury where shoes are indicated, it is again crucial to closely monitor recovery times and seek to address root causes above all else. Working with a competent hoof care professional is key in these situations.
From a personal standpoint, I have seen all four of my horses thrive barefoot. Each coming from situations where shoes were previously a regular part of life. Their recovery was not quick or easy but with patience and other therapeutic support they were able to grow and develop new viable feet within the first year. Hoof boots quickly became our friend and one of the most valuable investments I have ever made in my horses. Arthritic pathologies dwindled away, and soundness issues rarely present these days with respect to the feet. Overall, though, I think the most important and evident changes presented was in the rest of their bodies. Improved spinal mobility, increased joint range of motion, development of muscles in previously atrophied areas, and almost no more digestive issues (regular pain free movement is key for digestion). When the feet were in pain, they lacked the ability to move freely, and their bodies suffered the consequences. As an equine and human therapist, functional movement patterns (i.e., biomechanics) are always a major goal of therapy and the reason behind me sharing this perspective.
Works Cited
Bowker, R. M., Linder, K., Sonea, I. M., & Guida, L. A. (2010). Sensory nerve fibres and receptors in equine distal forelimbs and their potential roles in locomotion. Equine Veterinary Journal, 27(S18), 141–146. https://doi.org/10.1111/j.2042-3306.1995.tb04907.x
Budras, K.-D. (2009). Anatomy of the horse. Schlütersche.
Clayton, H. M., Gray, S., Kaiser, L. J., & Bowker, R. M. (2011). Effects of barefoot trimming on hoof morphology. Australian Veterinary Journal, 89(8), 305–311. https://doi.org/10.1111/j.1751-0813.2011.00806.x
Clayton, H. M., & Hobbs, S. J. (2019, May). Ground Reaction Forces: The Sine Qua Non of Legged Locomotion. Journal of equine veterinary science. https://www.ncbi.nlm.nih.gov/pubmed/31084749.
Kauffmann, S., & Cline, C. (2018). The essential hoof book: the complete modern guide to horse feet: anatomy, care and health, disease diagnosis and treatment. Trafalgar Square.
Kent, M. (1994). The Oxford dictionary of sports science & medicine.
Malone, Sara R.; Davies, Helen M.S. 2019. "Changes in Hoof Shape During a Seven-Week Period When Horses Were Shod Versus Barefoot." Animals 9, no. 12: 1017.
M. Moleman, M. van Heel, P. van Weeren, W. Back. Hoof growth between two shoeings leads to a substantial increase of the moment about the distal, but not the proximal, interphalangeal joint. Equine Veterinary Journal, 38 (2006), pp. 170-174
D.K. Proske, J.L. Leatherwood, K.J. Stutts, C.J. Hammer, J.A. Coverdale, M.J. Anderson,
Effects of barefoot trimming and shoeing on the joints of the lower forelimb and hoof morphology of mature horses. The Professional Animal Scientist, Volume 33, Issue 4, 2017,
Tortora, G. J., Derrickson, B., Tortora, G. J., & Tortora, G. J. (2017). Tortora's Principles of anatomy & physiology. Wiley.
https://www.theequinedocumentalist.com
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