Keeping horses barefoot is gaining in popularity because of the benefits in hoof health and movement it can provide some horses.
Barefoot hoof trimming is designed to maximize the biomechanical efficiency of hoof function. It is favoured among horse owners who prefer more natural management of their equine companions.
When the barefoot hoof is in contact with the ground, blood flow increases within the hoof because the heel can expand in an unrestricted manner. In contrast, shoes prevent the natural expansion within the hoof capsule that occurs with ground contact.
Horses with barefoot hooves may develop a deeper digital cushion and thicker sole in comparison to those that are shod.
Because of these and other changes in their hooves, concussive energy is more sufficiently dissipated within the hoof rather than being transmitted into soft tissues and bony structures.
Transitioning horses to barefoot takes time. Working in conjunction with a certified trimmer and veterinarian is recommended to facilitate a successful transition.
Equine Hoof Anatomy
The equine hoof is a living organ that is designed to flex and absorb shock. It contains several structures that synergistically work together to enable movement of the foot.
The hoof capsule protects the coffin bone, also referred to as the pedal bone or P3. This capsule consists of highly vascular soft tissues on the inside (the corium).
The outermost layer of the hoof structure is comprised of a hard wall that protects the inner tissues including the laminae (laminar layers) of the foot. This outer layer also includes the sole of the hoof which protects the inner structures.
Multiple structures of the hoof are responsible for absorbing the impact of the hoof hitting the ground. They work together to distribute these concussive forces to prevent stress in the joints.
The frog, a soft pad located on the centre of the hoof sole, reduces shock forces within the hoof.
The digital cushion is a tough, fibrous structure that also absorbs concussive energy. When bearing weight, the heels and bars of the hoof expand in a sideways direction to facilitate additional shock absorption.
Attaching shoes to the equine foot to protect the hoof capsule is a centuries-old practice carried out since at least 400 B.C.
Most competition and pleasure horses are shod with shoes made of metal or another dense material to protect hooves from damage, provide support to the foot, and provide optimal traction.
Recently, there has been a trend among owners and riders to keep horses barefoot instead of shod.
Proponents of barefoot hoof care regimes believe this approach stimulates better hoof growth because the hoof in its natural state makes direct contact with the ground surface that horses are working or performing on.
Barefoot proponents believe that the sole of a horse’s foot reflects his or her health status.
According to barefoot trimming experts, a healthy equine foot should exhibit a slight concavity. This is naturally achieved if the epidermal and dermal layers of the hoof laminae are tightly connected. 
A barefoot trim, also referred to as a physiological trim, aims to promote healthy hoof development. This hoof care regime typically involves trimming the bars and walls of the hoof above the live sole and blending any flares in the hoof. Loose or dead material on the sole and the frog are also removed.
Hooves trimmed according to barefoot methods are bevelled on the bottom edge of the hoof wall to create a mustang roll. This roll on the edge allows for the hoof to easily break over the ground when contact is made.
Research studies have examined the functional and morphological differences between shod and barefoot hooves. Multiple differences have been observed.
One study investigated the effects of barefoot trimming on hoof morphology in seven horses over a 16-month period. Morphology was measured with lateral, dorsal, and solar view photographs and lateromedial radiographs taken at 0, 4, and 16 months. 
Bevelling the toe and involving the frog and bars in the weight-bearing function of the hoof resulted in the elevation of the heel angle and the angle of the pedal bone in relation to the sole.
Researchers concluded these changes may be beneficial in treating under-run heels and achieving an optimal angle of the pedal bone. 
A separate study of 98 shod and 69 barefoot-managed hooves showed significantly fewer underrun heels, steeper heel angles, wider heels, increased splaying, increased flaring, and larger frog size compared to the hooves of shod horses. 
Physiology of Barefoot Hooves
As the hoof lands heel first on the ground, the hoof capsule expands. This allows the hoof capsule to fill with blood which flows into the tissues and nerves of the foot. This also serves as a shock-absorbing mechanism to cushion the structures within the hoof capsule.
Shoes are applied to the hoof while in a contracted state, held up and not bearing weight. Once the shoe is applied, the hoof is unable to expand normally, potentially predisposing the foot to pathological processes.
Dr. Robert Bowker is a veterinarian and the director of the Equine Foot Laboratory at the College of Veterinary Medicine at Michigan State University. Bowker says that the equine foot should be trimmed so the rear portion of the foot, including the frog, contacts the ground. 
He has found that blood flow within the back part of the foot is a key mechanism for dissipating energy.
The equine foot is continuously adapting and reacting to environmental conditions. Horses’ hooves are sculpted by their environment, and not only by genetic influences.
Dr. Bowker hypothesizes that contact with the ground stimulates the rear of the foot to produce more fibrous and fibrocartilaginous tissue in the digital cushion. The more fibrous tissue present in the digital cushion, the greater protection against chronic foot problems.
Digital Cushion Depth
A study of 12 mature American Quarter Horses investigated the effects of barefoot trimming and shoeing on the joints of the forelimb and digital cushion depth over a period of 140 days. 
The study consisted of three phases including six weeks during which time the horses were barefoot trimmed (days 0-42), six weeks when the horses were shod (days 49-91) and another 6 weeks when the horses were barefoot trimmed again (days 98-140).
The study determined that mean digital cushion depth was greater in the barefoot phases compared to the shod phase. A deeper digital cushion can dissipate concussive forces more effectively than a shallow one.
Joint circumference increased during the shod phase in the horses being studied.  This potentially indicates an inflammatory response in the horses’ joints during the time they were wearing shoes.
Based on the changes noted in this study, the researchers concluded that hoof morphology is altered in shod forelimbs due to changes in lower limb action and hoof load dispersion. This could increase the risk of lameness over time.
A heel-first landing is seen in nearly all feral horses and most sound domestic horses. The blood flow and large surface area in the rear of the equine foot disperse the concussive forces experienced in the hoof as it hits the ground.
If the rear of the foot and frog do not touch the ground, energy is not adequately dissipated. The force is instead transferred into the soft tissues and bones of the foot.
Because these structures cannot dissipate energy properly, they become vulnerable to damage which can result in lameness.
In horses with underrun hooves, contact with the ground does not occur at the rear of the foot. This causes improper dispersion of concussive forces in the hoof.
In underrun hooves, ground contact occurs beneath the coffin bone rather than at the rear of the foot. This places pressure on the coffin bone, rather than distributing the force within the digital cushion.
Dr. Bowker recommends maintaining a short toe length and ensuring the back part of the foot is in contact with the ground.
When looking at the solar surface of the foot, one-third of the foot should be in front of the apex of the frog, and two-thirds should be behind to encourage a heel-first landing.
A shortened toe discourages the development of underrun heels. Research indicates that sole length is naturally decreased in barefoot hooves compared to shod hooves. 
According to Dr. Bowker, hooves should be trimmed regularly to keep the toe short. Hoof care should be carried out at five- to six-week intervals rather than over longer time periods. 
The results of a study involving 26 horses indicate that four- to six-week farrier intervals help prevent excess loading of hoof structures. This reduces long-term injury risks caused by cumulative, excessive loading. 
Maintaining Horses Barefoot
Several factors should be considered when making the decision to keep horses barefoot.
Some horses may need to wear shoes to address hoof issues or to perform expected work. Others may do very well or better if barefoot.
Barefoot Hoof Care Advantages
In horses that are barefoot, the heels make contact with the ground. This promotes beneficial changes within the hoof as it adapts to the forces exerted upon movement.
Changes that occur in barefoot horses impact the entire hoof structure. The thickness of the sole increases, the hoof develops a natural concavity, and the position of the coffin bone improves.
Barefoot hooves develop digital cushions with larger surface areas that provide more support to the entire foot and the structures within it.
As energy dissipation improves within the hoof, the horse may exhibit a longer stride and reduced soreness.
An additional benefit of keeping horses barefoot is the lower cost of hoof care since shoes are not used.
Barefoot is Not for All Horses
Not all horses are best served by going barefoot. In some cases, shoeing may be necessary to address conformation issues and hoof problems.
Shoes can also provide traction and protection on hard ground. Some horses will use temporary glue-on shoes or hoof boots as an alternative during competition or when training on hard ground.
Some owners report difficulties in transitioning their horses to barefoot if they have been previously shod.
Due to genetic factors or conditioning, some horses may not be able to adapt to going barefoot whereas others may only need shoes or boots under certain conditions such as for competition or trail rides on rocky terrain.
Transitioning a Horse to Barefoot
Horses need tim