More than 10 years of intensive research at Michigan State University has resulted in new recommendations for relief from navicular syndrome and other chronic foot ailments.

Robert Bowker, an equine veterinarian who is director of the Equine Foot Laboratory at the MSU College of Veterinary Medicine, is conducting research on the physiological function of the equine foot. He brings a solid background to this research position with a veterinary degree from the University of Pennsylvania’s College of Veterinary Medicine and a Ph.D in anatomy from its medical school.

As a result of teaching gross anatomy to MSU veterinary students since 1988, Bowker became interested in the equine foot, since he knew that the texts commonly used by students and veterinarians were often incorrect on this subject.

Capitalizing on his doctoral training in neurobiology, Bowker began to lookclosely at the nerves of the foot. His research was soon expanded to blood vessels, cartilage, bones of the foot and more recently to the role of hooves and laminae from both health and disease standpoints. Most of these research efforts are supported by the American Quarter Horse Association, the Grayson-Jockey Club Research Foundation, Inc. and private donations.

In the 1990s, Bowker began supplementing his scientific studies with field observations of the foot of the wild horse in order to better understand footcare concerns with the domestic horse.

Bowker’s research has led to the discovery of a wholly different theory on how the equine foot responds to ground impact. His research focused on the blood flow to and from the equine foot and the role that it plays in energy dissipation that was reported in 1998. (See “Check Out A New Theory About Foot Physiology” starting on page 11 of the December, 1998, issue of American Farriers Journal.) 

The results led Bowker to believe that the modern-day horse should be trimmed so that more of the back part of the foot — including the frog — bears the initial ground impact forces and weight. If the foot is trimmed so that the frog rests on the ground, he maintains that the back part of the foot should be stimulated to grow more fibrous and fibrocartilaginous tissue in the . The result is a hoof that can help overcome some chronic foot problems.

Physiological Trim


DEPRESSION THEORY. This theory emphasizes that the spine of the frog is pushed up into the digital cushion to compress it and then forces the lateral cartilages (ungual cartilage) outward while the digital cushion simultaneously absorbs energy.

While studying the frog, sole, blood flow and other parts of the equine foot, Bowker has determined that it is critical that they work together to make a “good” equine foot. The aim of his research is to use this acquired knowledge to prevent and better treat cases of navicular syndrome and other chronic foot ailments.

In close collaboration with farriers and veterinarians, Bowker and his students at the Equine Foot Laboratory have developed guidelines for a “physiological trim.” This is a trim that permits the tissues of the foot to function optimally in dissipating impact energies during foot contact with the ground.

“This physiological trim is the result of the continuous evolution of our research,” he says. “We’ve found that the back part of the foot and blood flow is a major mechanism for dissipating energy. Our research has shown that the equine foot is constantly adapting and responding to environmental conditions. Most feet are sculpted by their environment, rather than only by genetic influences. 

“From a neuro-anatomical point of view, the equine foot is designed to hit the ground heel-first. This concept of hitting the ground heel-first is seen in virtually all feral horses and the majority of sound domestic horses.” 

The researchers also determined that the back of the foot should be the largest surface, area-wise, for ground impact.

“This is very much like a woman wearing high-heeled shoes as opposed to sneakers,” Bowker says. “The more comfortable sneakers distribute the load over a larger surface area, versus the smaller area of a high-heeled shoe.” As a result, the impact load that’s distributed over a large surface area of the hoof can be better supported with minimal stress by the foot tissues.

Bowker says the horse’s high-volume blood flow through this region offers additional energy dissipation mechanisms. Coupled with the frog and the blood flow, this large surface area is what dissipates the energy. 

When the back part of the foot and frog don’t touch the ground, this impact energy is not dissipated, but is transmitted to the bones and other tissues of the foot. Since these tissues do not dissipate the impact energy well, the long-term result of insufficient energy dissipation results in chronic foot problems and lameness. With underrun feet for instance, Bowker says the ground contact area is usually under the coffin bone rather than under the back part of the foot.

Recommendations For Farriers


HEMODYNAMIC FLOW THEORY. Due to a complex interrelationship between the ungual cartilage and the digital cushion, the ungual cartilage varies in structure. It also possesses a projection that could extend from the ventral surface over the bars to the midline of the foot below the digital cushion. When the foot impacts the ground heel first with the bars and hoof wall along with the descent of the ungual cartilage within the foot, it forces the ungual cartilage outward by the upward thrust of the bars onto the medial projection of the ungual cartilage.

“What we are trying to do is work with Mother Nature and not fight her,” explains Bowker. “We can do this by keeping the toe short and the back part of the foot on the ground. In other words, it’s a matter of using a large dose of common sense.” 

The aim is to have a functional, physiologically sound foot. The way to achieve this involves three essential ingredients: the frog, the sole and the trim.

Ground The Frog

Bowker’s research has shown that the frog must sit on the ground. To get the frog resting on the ground, he suggests gradually lowering the heel. When the heel is not on the ground, the foot will start to contract and get smaller, similar to a woman wearing high heeled shoes. Once the frog is on the ground, the bars will contribute to supporting weight and much of the load will be supported by the sole.

This load is transmitted to the sole around the frog apex via the dirt that accumulates from the ground. “Dirt should be left in the foot,” explains Bowker. In other words, he believes your clients should not clean the feet unless a horse has been standing in a lot of manure.

Bowker further maintains that a foot with a high-cupped or dished-out sole and frog that is not sitting on the ground will not support its weight with the frog and solar surface. This goes back to the analogy mentioned earlier about high heels and a small surface area for weight bearing. This small surface area results in high loads being placed upon the foot that cause significant stress changes to the foot tissues.

“After the farrier is finished trimming the equine foot, one-third of the foot will be in front of the apex of the frog and  two-thirds behind it when viewed from the solar surface,” says Bowker. “This creates a short toe and encourages a heel-first landing.”

Gradually Lower The Heel

Bowker emphasizes that any changes to a horse’s feet should be made gradually. “If the frog is on the ground, the foot will do what Mother Nature intends it to do,” he says. “When the frog is on the ground, the heel will be low (not an underrun heel) and this is what the farrier should aim for. 

“But if the frog is not on the ground, the heel should be lowered gradually over a period of several weeks. This is important to allow the foot to adjust to the changes. Again, this is a matter of common sense: do these adjustments gradually, as opposed to all at once, and the foot will better adapt to these changes.” 

Bowker explains that a good way to determine if the frog is touching the ground is to try to insert a thin plastic ruler under the frog at the rear of the foot while the horse is standing on cement or asphalt. 

“If the frog is on the ground, you shouldn’t be able to slide the ruler under the frog,” he says. “If you can, it means the frog is not bearing a lot of weight, which is contrary to what it was designed to do.” 

By comparison, he says the trimming methods used on many of today’s horses not only allow you to slide a ruler under the frog, but also your fingers and even part of your hand.

Bowker emphasizes caution in trimming. He says you should not trim much, if any, of the frog — especially the swollen area that is 4 or 5 centimeters (1 1/2 to 2 inches) behind the apex of the frog. He finds that farriers tend to remove this cushioned area by trimming straight back.

“When looking at the solar surface of  the foot, you should not trim and remove much of the frog,” he says. “The goal is to trim the foot so the frog is resting on the ground.” 

Don’t Touch The Sole!

Bowker says the goal with this method is to trim the foot to increase the surface area of the weight-bearing surface of the solar part of the foot.

“When the farrier is trimming, he or she should try to get to the sole plane — the grayish, waxy part of the sole that will appear after the dry, scaly superficial part of the sole has flaked off,” he says. “This should be done on the edge of the sole by the quarters of the hoof wall.”

The result of using this trimming method should reveal the plane of the live sole relative to the rest of the foot. Once this has been established, the farrier doesn’t need to remove any sole or frog in future trimmings. In fact, Bowker says the farrier’s goal should be to leave as much sole as possible. 

“In feral horses, the sole thickness is twice as thick as that of the domestic horse,” he says. “This is why feral horses can run and walk over most surfaces without any tenderness in the foot.

“Once the farrier is satisfied with the sole plane and coffin bone alignment, he or she shouldn’t have to touch the sole or the frog very much, if at all,” says Bowker. “There often is a tendency to remove too much sole, which creates a high arch. While this lessens the chance of the horse landing on small rocks and therefore having tender feet,  it encourages significant stress in the coffin bone.”

But, in a “bad-footed” horse with chronic lameness, the farrier will have to get to the sole plane in order to trim the sole in relationship to that sole plane. This levels the plane of the sole in relationship to the plane of the coffin bone.

Bowker believes the foot should be trimmed regularly and at 5- to 6-week intervals to keep the toe short. Frequent trims let you maintain the foot in as close-to-perfect condition as you can as opposed to trimming at very long intervals.

Bowker also emphasizes that the bars should not be removed. “They are there for a reason,” he says. “Leave the bars so that they are a little bit lower (shorter) than the hoof wall — with ‘a little bit’ meaning a fraction of a millimeter. But obviously, if the bars have overgrown the horn, they need to be trimmed, but not removed — again this is a matter of common sense.”

One-Third, Two-Thirds

Bowker says one of the goals of the “physiological trim” — as previously mentioned — is that one-third of the foot should be in front of the apex of the frog with two-thirds left behind. 

“If you have a foot where one-half to two-thirds of the foot is in front of the apex of the frog, you now have a foot in which the sole and foot relationships are out of balance,” he says. “The toe will be much too long. 

“The farrier, in consultation with a veterinarian, may request radiographs to discover where the coffin bone is in relationship to the hoof wall if this one-third and two-thirds ratio is out of alignment. By marking the apex of the frog with a thumbtack and a wire on the dorsal hoof wall, lateral radiographs will demon-strate the relationship of the coffin bone to the external foot structures.

 “Once you demonstrate where the tip of the coffin bone and frog apex are, you can generally measure 1 1/4 to 1 1/2 inches in front of the apex of the frog to locate where the new toe will be. In horses with long toes, the farrier should be trimming behind the white line.

“Once you are confident where these internal structures are in relationship to the hoof and sole, the farrier can prepare the foot for this one-third and two-thirds trim. It is OK to trim the toe area by rounding it off. Again, another common sense note is that if you are unsure where the internal structures are located, consultwith a veterinarian to obtain radiographs. But once you become aware and experienced with the sole callus and other sole features, radiographs may not always be necessary."

Shoe Selection Is Critical

One problem with this trimming theory is that shoes can create concerns. “If the horse must have shoes, the problem results in the frog being elevated from the ground,” says Bowker. “Therefore, it isn’t touching the ground and doing its job of bearing weight. The physiological function of the foot is compromised and the foot begins to contract.

“Some farriers have started trimming the foot so the frog is as close to the ground as possible — even touching the ground — when the horse has shoes on. Therefore, if the horse has to have shoes, this is the next best option.”

For barefoot horses with tender feet, Bowker says the foot will adapt to whatever environmental surface the horse is standing on. Yet a problem can arise when a horse is bedded on soft surfaces, such as straw, shavings, rubber mats, etc., and the owner expects them to walk, trot or gallop on rocks. 

“There are hundreds of barefoot endurance horses that are housed and trained on hard-packed surfaces such as hard dirt, gravel and small rocks without  tender feet,” he says. “The environment is the major determinant of a healthy foot rather than genetics. Again, it is a matter of common sense — the foot will adapt to its environment. However, I don’t recommend that horses be kept on cement.”

Turning A Bad Foot Into A Good Foot

Bowker recommends using these trimming techniques conservatively to gradually turn a bad foot into a good foot. By doing so, you give the foot time to adjust. The physiological trim as described here and greater movement — rather than stall rest — are critically important to producing a good foot, regardless of the breed of horse.

Over the past year, Bowker has received dozens of letters and e-mails from owners and their veterinarians asking about their horses’ prognosis with navicular syndrome. Some of these horses have been through all sorts of pads, bar shoes, acupuncture and pain management therapy, with little or no improvement.

However, by removing the shoes and using this "physiological trim" to lower the heels to get the frog on the ground, he says horse owners and veterinarians have indicated that the feet responded and began to become sounds within 6 to 8 weeks.

Additional information is available in two articles, "New Theory May Help Avoid Navicular" and "A New Theory About Equine Foot Physiology" at