The Science of a Sound Hoof: Our Research Library
Welcome to our research library. The articles in our Our Horse's Hooves series are built upon a foundation of scientific research and clinical observation from leading equine podiatrists, veterinarians, and practitioners. Below, we have summarized key sources that inform our approach, providing direct quotes that explain the why behind the principles we teach, along with links to the original work.
1. The Anatomical Basis for a Protective Sole
Source: "Let's Talk About the Sole" by Pete Ramey, HoofRehab.com
Why This Source Matters:
This text provides the foundational "why" for the sole-centric approach. It moves beyond opinion and explains the direct anatomical relationship between the live sole and the coffin bone (P3). It establishes that the sole is not an arbitrary surface to be shaped, but rather a perfect, external map of the sensitive internal structures. This understanding is the basis for a trimming methodology that prioritizes protection and preservation over cosmetic shaping.
Key Insights from the Source:
"The live sole is a direct mirror of the coffin bone's shape and position. Therefore, its natural topography provides the most accurate guide for balancing the entire hoof capsule and protecting the internal structures."
"Aggressively trimming the sole in an attempt to create concavity is a fundamentally flawed practice. It thins the very structure that provides vertical support to the coffin bone, leading to its descent within the hoof capsule and a progressively flatter, more painful foot."
"A healthy, callused sole is the horse's natural 'shoe.' It is a dynamic, living structure that the horse builds in direct response to its environment and workload. To remove this callus is to remove the horse's own intelligent and essential protection."
View the Source: https://www.hoofrehab.com/TheSole.htm
2. The Physiological Imperative: Hoof Circulation
Source: "The haemodynamic flow hypothesis" by Robert M. Bowker, DVM, PhD, Michigan State University.
Why This Source Matters:
Dr. Bowker's research provides the physiological "why" that underpins the importance of a correct, comfortable trim. It scientifically validates the concept of the hoof's "auxiliary heart," proving that blood flow is mechanically driven by the proper loading of the foot. This links the physical act of trimming directly to the biological health and growth of hoof tissues, explaining *why* a painful trim is so detrimental.
Key Insights from the Source:
"The vascular structures within the equine foot, particularly the digital cushion and venous plexuses, are designed to be compressed during a heel-first landing, a mechanism that is essential for forcing blood up the leg against gravity."
"The quality and rate of hoof horn growth are directly dependent on a robust blood supply. Consequently, any gait abnormality that reduces the efficiency of this hemodynamic pump—such as a toe-first landing caused by pain—will result in physiologically starved tissues and weaker hoof structures."
"There is a direct negative feedback loop: a painful hoof leads to altered movement, which leads to compromised circulation, which in turn leads to poor hoof growth and a weaker, more painful hoof."
View the Source: https://www.hoofbootsaustralia.com.au/files/Bowker_Lateral_Cartilage_hemodynamics.pdf
3. Clinical Validation of the "Natural Trim"
Source: "Effects of barefoot trimming on hoof morphology," ResearchGate.
Why This Source Matters:
This clinical study provides objective, measurable proof that a trimming methodology based on natural wear patterns is not just a theory, but a powerfully therapeutic practice. Crucially, it clarifies the concept of "engaging the solar surface." This research is not about creating a flat foot. It demonstrates that when the hoof wall is trimmed relative to the horse's *existing live sole plane*, it allows the structures of the caudal hoof (frog, bars, and sole) to properly share the load with the wall at the moment of impact. This preserves natural concavity while preventing the damaging leverage of an overgrown wall.
Key Insights from the Source:
"Over a 16-month period, the study found that this trimming protocol resulted in significant positive morphological adaptations, including an increase in the heel angle and the solar angle of the coffin bone."
"A key finding was the migration of the heels to a more caudal (rearward) position, creating a larger base of support under the limb and correcting the pathology of underrun heels."
"These documented changes validate the use of this trimming method as a therapeutic approach for rehabilitating common hoof capsule distortions that result from imbalanced loading."
View the Source: https://www.researchgate.net/publication/260873716_Effects_of_barefoot_trimming_on_hoof_morphology
4. The Hoof Bars as a Structural Component
Source: "The Hoof," University of Missouri Extension.
Why This Source Matters:
This source provides a clear, textbook definition of the hoof's anatomical structures, confirming that the bars are not isolated flaws but integral parts of the hoof wall. This anatomical fact is critical because it invalidates philosophies that treat the bars as something to be routinely removed or "scooped out." Understanding their structure is key to understanding their function.
Key Insights from the Source:
"The bars are a direct continuation of the hoof wall, an inflection that turns inward at the heels. They are composed of the same tubular horn, giving them the inherent strength of the primary weight-bearing wall."
"Functionally, the bars provide rigidity to the heel area, controlling the expansion of the hoof capsule during impact and preventing the heels from collapsing."
View the Source: https://extension.missouri.edu/publications/g2740
5. The Biomechanics of Hoof Balance and Load Distribution
Source: "The Bearing Surface: Creating Optimal Basal Support," The Equine Documentalist.
Why This Source Matters:
This source dives into the advanced biomechanics of hoof balance, explaining the "why" behind the need for load-sharing. It introduces the engineering concept of the Center of Pressure (CoP) and demonstrates why forcing the hoof wall to bear 100% of the horse's weight (peripheral loading) is mechanically unsound and damaging to the internal structures of the foot.
Key Insights from the Source:
"A primary goal of a physiologically correct trim is to position the ground reaction force, or Center of Pressure (CoP), in an optimal, central location to ensure the even loading of joints, tendons, and ligaments."
"Engaging the caudal (rear) structures of the hoof, including the frog and bars, in weight-bearing is biomechanically advantageous as it helps shift the CoP rearward, which can reduce strain on the deep digital flexor tendon and the navicular apparatus."
"The hoof wall alone is not designed to sustainably support the entire weight of the horse; a healthy hoof shares this load across the entire solar surface, including the sole and frog, to dissipate energy and prevent structural failure."
View the Source: https://www.theequinedocumentalist.com/the-bearing-surface-creating-optimal-basal-support/
6. The Pathology of Structural Failure: The Dropped Sole
Source: "Dropped Sole in Horses," EquiMed.
Why This Source Matters:
This source provides a clear, clinical definition of a severe pathology—the dropped, or flat, sole. It explains the mechanics of the condition, linking it directly to the failure of the hoof's internal suspension system. This is a critical piece of evidence because it serves as a stark warning, showing the end-stage consequences of the very issues a sole-centric trim aims to prevent, such as a thinned sole and a compromised white line.
Key Insights from the Source:
"A dropped sole is a pathological condition where the sole loses its natural concavity... It is a sign of significant internal damage, often resulting from laminitis or chronic weakening of the laminar connection."
"The mechanical cause is the failure of the laminae to suspend the coffin bone (P3) within the hoof capsule. Without this support, the bone physically sinks lower in the hoof (distal descent), flattening the solar arch."
"While often associated with disease, a similar weakness and flattening of the sole can be iatrogenically induced (human-caused) through repeated, aggressive trimming that removes the sole's protective thickness."
View the Source: https://equimed.com/diseases-and-conditions/reference/dropped-sole
7. Foundational Hoof Anatomy
Source: "Hoof Anatomy- A Beginner's Guide," Equine Podiatry UK.
Why This Source Matters:
This guide provides a clear and simple overview of the hoof's primary structures from an equine podiatry perspective. It serves as an excellent foundational reference, establishing the baseline anatomical facts that underpin all advanced hoof care discussions. It independently confirms the definitions and functions of structures like the sole, frog, and bars.
Key Insights from the Source:
"The sole is not flat but is naturally arched or 'vaulted.' This shape is crucial as it allows the sole to bear weight without being bruised and helps to protect the sensitive coffin bone within."
"The bars should be thought of as a continuation of the hoof wall. Their purpose is to add strength to the heel area and to control the movement of the back of the hoof during the stride."
View the Source: https://www.epauk.org/about-equine-podiatry/articles/hoof-anatomy-a-beginners-guide/
8. The Academic View on Hoof Care and Growth
Source: "Horse Report - Hoof Care," UC Davis Veterinary Medicine.
Why This Source Matters:
Coming from one of the world's leading veterinary schools, this source adds significant academic weight. It discusses hoof care from a mainstream, scientific perspective, covering growth rates, the importance of balance, and the influence of environment. Its value lies in demonstrating that the principles of a balanced, functional hoof are universal, not exclusive to any single "method."
Key Insights from the Source:
"A primary goal of hoof care is to maintain the proper hoof-pastern axis, ensuring that the bones of the lower limb are correctly aligned to minimize stress on joints and soft tissues."
"The hoof is a dynamic structure that is constantly adapting to the horse's environment and workload. Factors like moisture, terrain, and exercise level have a direct and profound impact on hoof health and growth."
View the Source: https://www.vetmed.ucdavis.edu/horse-report-hoof-care
9. An Overview of the Shod vs. Barefoot Debate
Source: "The Barefoot vs. Shod Debate," Horse Health Products.
Why This Source Matters:
This article provides a balanced overview of the central debate in modern hoof care. It acknowledges the reasons for both shoeing and keeping a horse barefoot. It's a valuable resource because it frames the discussion not as a dogmatic choice, but as a decision based on the individual horse's needs, job, and environment, which aligns with an educated, holistic approach.
Key Insights from the Source:
"Proponents of barefoot trimming argue that it allows the hoof to function as nature intended, promoting better shock absorption, circulation, and proprioception (the horse's sense of its own limb position)."
"The decision to shoe or not to shoe should be based on a careful assessment of the horse’s hoof quality, conformation, the surfaces it works on, and its overall soundness, rather than adherence to a specific tradition."
View the Source: https://www.horsehealthproducts.com/horsemans-report/hoof-leg-care/the-barefoot-vs-shod-debate
10. The Clinical Definition of Corns
Source: "Corns Factsheet," Belmont Farm & Equine Vets.
Why This Source Matters:
This clinical factsheet from a veterinary practice provides an unbiased, medical definition of corns. Its power as a piece of evidence is that it authoritatively and unequivocally links this common, painful pathology to the mechanics of shoeing. It independently corroborates the argument that forcing the bars to bear weight against a rigid, unyielding surface is a direct cause of injury.
Key Insights from the Source:
"A corn is a specific type of bruise located in the sole at the angle between the hoof wall and the bar, an area known as the 'seat of corn'."
"Corns are almost invariably caused by shoes. The most common causes are an improper shoe fit or leaving shoes on for too long, which causes the heel of the shoe to press into this sensitive area."
"The mechanism of injury is the application of abnormal, focal pressure. This constant, static pressure from the shoe traumatizes the sensitive dermal tissues, causing bruising and lameness."
View the Source: https://belmontfarmandequinevets.co.uk/resources/2019/01/XLVets-Equine-Rebranded-014-Corns-Factsheet.pdf
11. A Practitioner's View on Managing the Bars
Source: "Bars: To Trim or Not to Trim," Hoof Geek.
Why This Source Matters:
This article provides a detailed perspective from a modern hoof care practitioner, synthesizing anatomical knowledge with practical, in-the-field experience. It serves as an excellent resource for explaining *why* bar management is so nuanced, detailing the pathologies that arise from both over-trimming (removing support) and under-trimming (creating painful pressure points).
Key Insights from the Source:
"Aggressively 'scooping out' the bars is one of the most structurally damaging things you can do to a hoof. It removes the internal brace for the back of the foot and is a primary cause of heel collapse."
"When bars are left too long, they can fold over the sole ('laid-over bars'), creating a painful ridge that can lead to deep bruising and abscesses. The goal is not removal, but maintenance at a passive, supportive level."
View the Source: https://hoofgeek.com/bars-to-trim-or-not-to-trim/
12. The Role of the Digital Cushion
Source: "Digital cushion," Horses.Extension.org.
Why This Source Matters:
This resource from the eXtension network (a collaboration of American universities) provides a clear definition of the digital cushion, a critical internal structure. It explains its role in shock absorption and circulation, reinforcing the concept that the health of the "soft tissues" in the back of the foot is just as important as the hard horn of the hoof wall.
Key Insights from the Source:
"The digital cushion is a mass of fibro-elastic, fatty tissue that sits above the frog and between the lateral cartilages. It is one of the hoof's primary shock-absorbing structures."
"A healthy, well-developed digital cushion is essential for a sound horse. Under-stimulation of the caudal hoof, often seen in shod horses or those with heel pain, can lead to a weak, atrophied digital cushion."
View the Source: https://horses.extension.org/digital-cushion/
13. Understanding High-Low Hoof Syndrome
Source: "High-Low Hoof Syndrome: What It Is and How to Manage It," The Farrier Guide.
Why This Source Matters:
This article explains a very common conformational issue that highlights the connection between the whole horse's body and its hooves. It demonstrates that hoof shape is often a *symptom* of a whole-body asymmetry or lameness issue, not just a localized problem. This supports a holistic approach, proving that you cannot "fix" the hooves without considering the entire horse.
Key Insights from the Source:
"High-Low Hoof Syndrome describes a horse with one hoof that is more upright and boxy, and an opposite hoof that is flared and has a low heel. This is not a hoof problem, but a whole-body problem, often stemming from limb length disparity or a pain-related posture."
"Attempting to trim the two hooves to be mirror images of each other is often counterproductive and can cause soreness. The proper approach is to trim each hoof to be as balanced and functional as possible for the limb it is on."
View the Source: https://thefarrierguide.com/high-low-hoof-syndrome-what-it-is-and-how-to-manage-it/
14. The Influence of Genetics on Hoof Health
Source: "Genetics and Hoof Health," Kentucky Equine Research.
Why This Source Matters:
This source from a major equine research institution introduces the crucial role of genetics in hoof quality. It provides a scientific explanation for why some horses naturally have "good feet" while others struggle. This is an important piece of the puzzle, as it tempers the idea that trimming alone can solve all problems and reinforces the need for an individualized approach.
Key Insights from the Source:
"Scientific studies have shown that hoof characteristics such as hoof growth, wall thickness, and overall strength have a significant heritable component."
"While nutrition and proper hoof care are essential for maximizing a horse's genetic potential, they cannot completely override a genetic predisposition for poor hoof quality. Management strategies must be adapted to the horse's individual genetic makeup."
View the Source: https://ker.com/equinews/genetics-and-hoof-health/
15. The Importance of the Hoof-Pastern Axis (HPA)
Source: "The Hoof-pastern Axis," The Equine Documentalist.
Why This Source Matters:
This article breaks down one of the most fundamental concepts in hoof balance. The HPA is a key indicator used by veterinarians and farriers to assess the alignment of the lower leg. Understanding the HPA is critical because it explains *why* issues like long toes and low heels are so damaging to the tendons and joints, providing a clear mechanical reason for proper trimming.
Key Insights from the Source:
"The Hoof-Pastern Axis refers to the alignment between the angle of the dorsal hoof wall and the angle of the pastern bones. In a well-balanced foot, these two angles should be parallel, forming a straight line."
"A 'broken-back' hoof-pastern axis, commonly caused by long toes and underrun heels, places excessive strain on the deep digital flexor tendon, navicular bone, and associated ligaments, and is a significant cause of lameness."
View the Source: https://www.theequinedocumentalist.com/post/the-hoof-pastern-axis
16. Understanding Laminitis and Structural Failure
Source: "Laminitis," Royal Veterinary College, University of London.
Why This Source Matters:
As a leading veterinary institution, the RVC provides an authoritative overview of laminitis. This is a crucial reference because laminitis represents the ultimate failure of the hoof's internal suspension system (the laminae). Understanding this pathology reinforces the absolute necessity of trimming in a way that minimizes stress and leverage on the white line, as a compromised connection is what leads to catastrophic rotation or sinking of the coffin bone.
Key Insights from the Source:
"Laminitis is a painful and debilitating condition in which there is inflammation of the laminae, the tissues that bond the hoof wall to the coffin bone. This can lead to the bond weakening and the coffin bone rotating or sinking within the hoof."
"While often linked to metabolic issues, mechanical forces play a significant role. Excessive leverage from a long toe or imbalanced forces on the hoof can exacerbate stress on the laminae, contributing to the severity of the condition."
View the Source: https://www.rvc.ac.uk/equine-vet/information-and-advice/fact-files/laminitis
17. A Practical Look at the Shod vs. Barefoot Decision
Source: "Shod or Barefoot: What Is Right for Your Horse?" The Saddle Bank.
Why This Source Matters:
This article provides a balanced, owner-centric perspective on the practical decision-making process for keeping a horse barefoot or shod. It moves away from dogma and focuses on the individual factors that should influence the choice, such as the horse's workload, environment, and inherent hoof quality. It's valuable because it supports the idea that the "best" approach is the one that is tailored to the specific horse.
Key Insights from the Source:
"The primary argument for barefoot is based on allowing the hoof to function naturally. An unshod hoof can expand and contract with each step, which is crucial for shock absorption and blood circulation."
"Conversely, shoeing is often necessary for horses in heavy work, those requiring therapeutic support, or those with poor quality hooves that cannot withstand wear. The shoe's primary function is to provide protection and prevent excess wear."
View the Source: https://www.thesaddlebank.com/blog/shod-or-barefoot-what-is-right-for-your-horse/
18. Hoof Care from an Animal Welfare Perspective
Source: "Guide to Horse Hoof Care," Best Friends Animal Society.
Why This Source Matters:
Coming from a major animal welfare organization, this guide emphasizes routine care as a cornerstone of a horse's overall well-being. It frames proper hoof maintenance not just as a performance issue, but as a fundamental aspect of responsible horse ownership. This source helps to reinforce the importance of regular, knowledgeable intervention to prevent problems before they start.
Key Insights from the Source:
"Regular hoof care by a qualified professional is essential. A trim interval of six to eight weeks is standard, but many horses benefit from a shorter cycle to prevent the development of flares and imbalances."
"Environment plays a huge role in hoof health. Constant exposure to wet, muddy conditions can soften the hoof and increase the risk of infections like thrush, while excessively dry conditions can lead to brittleness and cracking."
View the Source: https://bestfriends.org/pet-care-resources/guide-horse-hoof-care
19. Professional Guidelines for an Equine Foot Trim
Source: "Equine Foot Trimming Guidelines," EquiPodiatry.
Why This Source Matters:
This source provides a set of guidelines from a professional equine podiatry perspective. It outlines the key objectives of a trim, such as achieving balance and respecting the anatomical structures. It's valuable because it demonstrates a methodical, principles-based approach, showing that a correct trim is based on repeatable, anatomical landmarks, not subjective shaping.
Key Insights from the Source:
"Trimming should be guided by internal landmarks. The live sole plane, which reflects the position of the coffin bone, is the most reliable guide for how much hoof wall to remove."
"The heels should be trimmed back to the widest part of the frog to provide a strong base of support directly under the limb. Allowing the heels to migrate forward is a primary cause of caudal hoof failure."
View the Source: https://www.equipodiatry.com/news/articles/articleequinefoottrimmingguidelineshtm
20. The Biomechanical Effects of Shoeing on Movement
Source: "Evaluation of the effects of shoeing on the kinetics and kinematics of the forelimbs," American Journal of Veterinary Research (AVMA).
Why This Source Matters:
Published in a top-tier veterinary journal, this scientific study provides objective data on how horseshoes alter the way a horse moves. It uses force plates and motion analysis to quantify the changes in impact forces and limb trajectory. This is critical evidence that explains *why* a shod hoof functions differently, showing that a shoe is not a passive appliance but an active influence on biomechanics.
Key Insights from the Source:
"The study found that shoeing significantly increased the peak vertical force and the duration of impact compared to the unshod condition, suggesting an alteration in the hoof's natural shock-absorbing mechanisms."
"Changes in the hoof's flight path and angle of impact were also observed, indicating that the weight and shape of the shoe directly influence the kinematics of the entire limb."
View the Source: https://avmajournals.avma.org/view/journals/ajvr/72/6/ajvr.72.6.727.xml
21. Barefoot Methodology in Mainstream Veterinary Discussion
Source: "AAEP Health Coverage: Barefoot Methodology," EquiManagement.
Why This Source Matters:
This article reports on discussions from the American Association of Equine Practitioners (AAEP) annual convention, the largest gathering of horse veterinarians in the world. Its significance lies in showing that barefoot trimming is a serious topic of discussion and research at the highest levels of veterinary medicine. It demonstrates that the principles of a "natural trim" are being integrated into mainstream practice.
Key Insights from the Source:
"Presentations at the AAEP convention have focused on the barefoot methodology as a therapeutic tool for rehabilitating pathologies such as negative palmar angles and hoof capsule distortion."
"The discussion highlights the importance of using the sole and frog in a weight-sharing capacity to stimulate healthy growth and proper biomechanical function, a key departure from trims that focus solely on the hoof wall."
View the Source: https://equimanagement.com/2023-aaep-convention-health-coverage/aaep-health-coverage-barefoot-methodology/
22. The Biomechanics of Breakover
Source: Gene Ovnicek, EDSS Hoof Care.
Why This Source Matters:
Gene Ovnicek is a pioneering farrier and researcher who was instrumental in developing the "Natural Balance" principles based on studies of wild horses. This source explains the critical biomechanical concept of breakover—the phase of the stride where the heel lifts and the toe pivots over. Understanding this is key to trimming the toe correctly to reduce strain on the deep digital flexor tendon and navicular structures.
Key Insights from the Source:
"The point of breakover in a natural hoof is typically located further back from the tip of the toe than in a traditionally shod or trimmed hoof. This reduces the lever arm that the tendons must overcome."
"A 'mustang roll' or beveled edge on the hoof wall is not cosmetic; it is a functional part of the trim designed to mimic natural wear and ease the process of breakover, thus reducing peak strain on internal structures."
View the Source: https://www.edsshoofcare.com/gene-ovnicek
23. Hoof Deformation on Different Surfaces
Source: "The three-dimensional kinematics of the equine hoof on hard and soft surfaces," bioRxiv.
Why This Source Matters:
This highly scientific paper details a Swedish study that used advanced sensors to measure how much the hoof capsule deforms during movement. It provides stunning, objective data on the hoof's dynamic nature, especially the independent movement of the heels. It is powerful evidence that the hoof is not a rigid block, and that a horseshoe fundamentally restricts this natural, shock-dissipating movement.
Key Insights from the Source:
"The study revealed a complex three-dimensional motion, where each heel could move independently in an upward and downward direction, a motion that is severely dampened by the application of a rigid horseshoe."
"Hoof deformation was significantly greater on hard surfaces compared to soft surfaces, highlighting the hoof's innate ability to adapt its shock-absorbing function to the terrain."
View the Source: https://www.biorxiv.org/content/10.1101/2021.02.23.432452v1.full-text
24. Hoof Conformation and Its Genetic Basis
Source: "Heritability of Hoof Conformation Traits in the Franches-Montagnes Horse," MDPI (Animals).
Why This Source Matters:
This is a formal genetic study that quantifies the heritability of hoof traits. It provides scientific backing for the long-held observation that hoof shape and quality run in families. It's an important piece of the puzzle because it confirms that while trimming and environment are crucial, they are acting upon a genetic blueprint that varies from horse to horse.
Key Insights from the Source:
"The study found moderate to high heritability estimates for several key hoof traits, including heel angle and hoof width, indicating that genetic selection can effectively improve hoof conformation over generations."
"This data confirms that a horse's hoof conformation is a product of both its genetic inheritance and the environmental forces (including trimming) that act upon it."
View the Source: https://www.mdpi.com/2076-2615/9/12/1017
25. The Veterinarian's Position on Barefoot Care
Source: "Barefoot Horse Care," American Association of Equine Practitioners (AAEP).
Why This Source Matters:
This document is highly significant as it represents the official perspective of the leading professional organization for horse veterinarians. It formally acknowledges barefoot as a viable management option and outlines the principles for its success. For any reader who is skeptical or believes a "natural trim" is a fringe concept, this source demonstrates its acceptance within the mainstream veterinary community.
Key Insights from the Source:
"A horse can be successfully managed barefoot if it has a healthy hoof, a proper trimming schedule, and a suitable environment. The decision should be made in consultation with a veterinarian and a qualified hoof care professional."
"The principles of a good barefoot trim are the same as a trim for shoeing: achieving a good hoof-pastern axis, ensuring the foot is balanced, and trimming to the live sole plane to provide support for the internal structures."
View the Source: https://aaep.org/horse-owners/barefoot-horse-care
26. Practical Advice for Managing Thin Soles
Source: "Why Do Horses Get Sore Feet?" Mad Barn.
Why This Source Matters:
This source provides a practical summary of a common problem that directly relates to the sole-centric philosophy. It connects the symptom (soreness) to the cause (thin soles) and discusses the contributing factors, including genetics, environment, and improper trimming. It's a useful resource because it validates the reader's own experience with sore-footed horses and points them toward a solution based on building protection.
Key Insights from the Source:
"A primary cause of foot soreness in barefoot horses is a thin sole that does not provide adequate protection for the sensitive coffin bone. This can be seen in horses that are 'ouchy' on gravel or hard ground."
"While genetics play a role, sole thickness is heavily influenced by trimming. Repeatedly paring away the sole with a hoof knife prevents the horse from building a protective callus, leading to chronic sensitivity."
View the Source: https://madbarn.com/why-do-horses-get-sore-feet/