What researchers know about the biomechanics of the barefoot hoof

It looks like an ultra-resistant all-weather block, with a shiny, marblelike surface that can trick us into thinking it’s indestructible. Its sharply defined edges give us the impression that it’s as solid as stone—especially when they land with full force on one of our own feet. And its “clip clop” sound striking against hard surfaces betray it as a dense support structure that works like a steel foundation under massive forces.

In reality, though, the equine foot isn’t like this at all.

The foot—or, essentially, the one long toe—is a complex structure filled with bones, tendons, ligaments, arteries, veins, nerves, cartilage, joint fluid, and more. Far from being inert, it’s alive and very active, communicating sensory information, pumping blood, and articulating, contracting, and flexing over ground. And if it’s unshod, it’s constantly changing shape as the horse uses it, instantaneously as well as over time.

The science of the equine foot is like the hoof itself—expanding and contracting, getting shaped and trimmed. But as researchers continue to learn more, we can benefit from their knowledge, better understanding how our horses’ feet work. And with that knowledge, we can hope to improve the health of not only the feet but also the entire horse. 

The Evolution of the Hoof

The earliest equids, which were the size of foxes, had five-toed feet. They didn’t need these toes to grab things, however, benefiting more from better limb swing to run faster. So each middle toe evolved to grow longer and the side toes became shorter. Eventually, the first and fifth toes disappeared, while the second and fourth ones turned into the modern-day splint bones on the sides of each cannon bone.

Recently, though, scientists determined that the splint bones are only the top parts of those toes. The bottom parts are still in the foot, says Nikos Solounias, PhD, of the New York Institute of Technology College of Osteopathic Medicine (NYITCOM), in Old Westbury. What we know as the V-shaped frog is actually what’s left of the bottom of toes two and four, he says.

In his research Solounias followed markers in the embryonic development of the equine foot, which starts out like an unopened tulip with all five toes as its petals. In the adult horse the markers indicate that the top parts of toes one and five appear as bony processes (“wings”) coming off the coffin bone. The bottom parts of those two toes make up the ridges along the sides of the frog. 

So in some ways, he’s still got five toes in that foot—but four are in “very embryonic form,” says Solounias.

“We don’t know the role of these remnant structures in the real function of the horse,” he says. “It could be more for the sensation from the nerves of the five digits and their relation to the brain than actual locomotor mechanics. We’re seeing things from a different perspective, and it’s important to understand how evolution worked to lead us to the modern horse.”

A Multipurpose Structure

The foot reacts to movement, pressure, and the environment. Unshod, it can react more freely, without the constraints of a rigid interface.

“The foot should expand when it receives weight,” says Hilary Clayton, BVMS, PhD, MRCVS, Dipl. ACVSMR, McPhail Dressage Chair Emerita at Michigan State University (MSU) and president of Sport Horse Science, in Mason, Michigan. “Its structures help absorb the shock from the force when the foot comes down on the ground.”

If the foot is bare (and trimmed correctly), forces spread across the bottom of it—throughout the sole, wall, frog, digital cushion, heels. All these more-or-less-elastic tissues receive diffused impact, while structures higher up the leg, such as the pastern, fetlock, knee, and hock, don’t experience as much of it.

Meanwhile, each footstep plays a vital role in healthy circulation, says Stephen O’Grady, DVM, of Virginia Therapeutic Farriery, in Keswick. “The blood vessels in the equine foot have no valves,” he says. “Arterial blood comes into the foot when the horse lifts up his foot, the vessels fill with blood, and it gets utilized. So, when he puts weight on the foot, thousands of capillaries across the entire solar surface of the foot get compressed, pushing blood back toward the heart.”

Work by Clayton’s colleague Robert Bowker, VMD, PhD, professor and head of MSU’s Equine Foot Laboratory, indicates that heels also have critical sensors for proprioception—the sense that tells horses where they’re putting their feet. “They might not feel as well as we do, but it’s significant that the proprioceptors are in the soft horn of the heel where the wall is able to move the most,” Clayton says.

The healthy bare foot usually has thicker soft tissue structures on its bottom surface, including the digital cushions. And that could possibly have protective qualities, says Debra Taylor, DVM, MS, Dipl. ACVIM, associate professor and equine podiatry veterinarian at Auburn University’s College of Veterinary Medicine, in Alabama. “When the digital cushion is skinny and long (which is more common in shod horses, she notes), it only supports the center of the navicular bone,” she says. “The edges won’t have any soft tissue under them; there’s just the deep digital flexor tendon (DDFT) directly. So it’s only intuitive that if the digital cushion is wide enough, it would have some sort of protective role.”

How the bare foot functions from a scientific standpoint is not necessarily what happens when shoes are added, our sources say. Shoes can constrict movement and restrict expansion by forcing the hoof into a certain shape. And they prevent the bottom of the foot from coming into full contact with the ground. They say the resulting lack of stimulation from the ground tends to make the soft structures recede, contract, become softer, and, in some ways, atrophy.

What Should a Bare Foot Look Like?

Despite having this basic biomechanical knowledge, scientists still don’t clearly understand how a domesticated horse’s bare foot should appear, says Taylor. “It’s the only tissue on the horse where veterinarians can’t agree on what’s normal,” she says.

Research is lacking significantly, she says. In fact, scientists continue to debate the existence of some anatomical structures. “There’s a ligament that other scientists have started recognizing recently, under the DDFT on top of the digital cushion, and it’s not even labeled in specialized anatomy books anymore,” she says. The late Prof. August Schummer, PhD, former head of the Veterinary Anatomy Department at Justus Liebig-Universitat, in Giessen, Germany, had described and labeled the ligament in the 1940s, but the structure later disappeared from literature, says Taylor.

One thing scientists seem to agree on, however, is that the wild or feral horse foot is not a reliable standard for the domesticated horse foot.

“Mustangs and brumbies are not a good model,” Clayton says. “They do a different kind of work.”

Wild horses never have to carry ­riders, never do true lateral movements or dressage work, and place lighter forces on their DDFTs and navicular bones, she says. “And they’re not free from pathology (disease or damage), either,” she adds.

Taylor says she’s currently working on research that will help better define what a fully developed domesticated equine foot looks like—as the horse’s development when it’s young appears to play a key role in a foot’s ability to support the forces of riding. “We are looking at how to measure heel structure and predict the volume and integrity of digital cushions and cartilages, through MRI and physical exams,” she says.

Good Husbandry for Bare Feet

Horses might have evolved to have great feet for their purposes but, somewhere along the way, humans saw a need to begin shoeing them. Shoes are a relatively recent phenomenon, popping up in the Middle Ages—at about the same time humans starting housing horses in stalls, says Angelo Telatin, PhD, associate professor of equine studies at Delaware Valley University, in Doylestown, ­Pennsylvania.

“The Romans worked and traveled with barefoot horses,” he says. “But more than a thousand years later, because of thieves and pirates, horses got moved into stalls inside castles. They couldn’t move, and they were standing in their own urine. And suddenly they started getting hoof problems.”

The key to healthy bare feet is letting horses roam, because movement stimulates growth, he says. Ideally, they should be moving on small, smooth rocks, like pebbles, or even stone dust (also known as screening). Mud, wet grass, and especially urine and feces can weaken the hoof structures, while harder and rougher footing strengthen them.

“The Romans had their horses in large paddocks on oval-shaped stones sticking up from the ground, so that the hooves were never standing in urine,” Telatin says. “But most horses today live on the equivalent of carpet. So it’s no wonder their feet can’t hold up to the demands of ridden work on variable surfaces.”

Telatin keeps all 50 of his university’s school horses barefoot—although two or three of them sometimes need front shoes for more challenging situations such as outings on rugged terrain.

On the other side of the globe, farrier Declan Cronin has kept nearly an entire training stable of Thoroughbred racehorses barefoot in Dubai, the United Arab Emirates. Hired by trainer Mike de Kock, Cronin worked with Taylor, following Bowker’s work, to maintain “as many horses as possible” unshod in the stables of Sheikh Mohammed Bin Khalifa Al Maktoum of the Dubai Royal Family. The horses race in shoes, per racing rules, but farriers remove them shortly thereafter.

Cronin says genetics probably plays a role in hoof health and that it’s important to select horses with quality hooves. Then, it’s critical to maintain them ­properly.

“We’re living in a world of manicured arenas, and that’s not stimulating healthy hoof growth,” he says. “You’ve got to work the horse and let it live; if he’s got a good foot, it will adapt to its environment. But you can’t keep him in a stall all day with fluffy bedding soaked in urine and feces and then ask him to go work hard under saddle on the track. That’s too big a jump for him.”

Working very young horses—­particularly racehorses—before their hooves are ready might also be bad practice for bare feet, Taylor says. “The hoof’s a smart structure, just like bone is,” she says. “We have to stimulate it just like going to a gym and getting the most of a workout. And they’re not going to get that from 45 minutes a day of training and 23 hours a day locked in a stall as a 3-year-old. These youngsters would likely benefit from being turned out on varied terrain with ample space for movement to stimulate and exfoliate their feet.”

Hooves and bones are still in development at that age and can continue to develop for years, she adds. In researching cattle she has seen the importance of building strong hooves and bones—including of the feet—by getting these animals moving across hard surfaces regularly from the time they’re babies.

The Barefoot Trim

Our sources agree that trimming a bare foot is an art requiring knowledge of the supporting science. It’s not terribly complicated, but people often get it wrong.

Two common mistakes, they say, are trimming the foot to look like a wild horse foot or trimming it like it’s going to receive a shoe.

“I prefer to call it shaping,” O’Grady says of the correct approach. “Just round the edges of the wall and let friction take care of the sole.”

He recommends trimming the heels and frog so these structures are on the same plane, and then rasping the hoof wall at a 45-degree angle on the outer side of the white line to create a bevel in the wall. If the bottom surface is slightly uneven, the farrier can level things off to ensure good force distribution, aka load-sharing. And if the sole is thick and strong, the trimmer can enhance breakover (the moment when the heel lifts off the ground and the toe rolls over during movement) by angling the toe slightly—just enough to slip a credit card between it and the ground, he says.

Leaving the horse to develop his own entirely natural shape might work if he isn’t ridden, but a working horse needs shaping to prepare his feet for the extra weight. Trimming the horse as though he’s going to get a shoe creates fragile side angles and removes too much sole.

Clayton and Bowker studied Arabian riding horses that had been barefoot for several years and started shaping their feet according to barefoot trimming principles, she says. They found that the feet changed shape over 16 months, leading to rounder hooves even in the hind limbs. And there was less variation in hoof shape from one horse to another. More importantly, the horses’ feet more closely reflected the goals of barefoot shaping: a wider frog, a thicker digital cushion as confirmed via radiographs, higher heel angles that more closely paralleled the dorsal wall, more sole concavity, and easier breakover.

Take-Home Message

Researchers are just starting to scratch the surface of how to blend the natural state of the equine foot with the less natural state of riding. It’s a field facing many debates, assumptions, and misunderstandings, making solid research all the more important as we move forward.