Research shines new light on shoeing practices

In A Handbook of Horse-Shoeing, published in 1898, Dr. A. W. Dollar described the correct manner for evaluating a horse prior to fitting shoes. "The horse must be seen both at rest and in motion," wrote Dollar, "the object being to form a clear idea of the conformation and action of the limb, of the form and condition of the hoof, of the way in which the horse brings the foot to, and lifts it from, the ground."

Until the last decade, this standard evaluation technique was taught and practiced largely unchanged since the days when Dollar was a veterinary surgeon and professor at the University of Edinburgh.

Evaluation of the movement of the horse was largely a matter of observation and experience and, eventually, according to Dollar, "the examiner makes up his mind whether the horse goes normally or not."

Over the last 10 years or so, however, everything about how veterinarians evaluate equine movement has changed. Research tools such as pressure-plate horseshoes, treadmills, force-plate recorders, slow-motion-capture video and computer-assisted gait analysis have allowed us to "see" the kinetics of a horse's movement in a whole new light.

This new light opened many exciting areas of research that ultimately will yield information of benefit to the horse, but also called into question some of the concepts and practices veterinarians had previously thought to be true and valuable.

It is a long way from Dollar's visual evaluation of the moving horse, followed by a clinical interpretation/impression of the lameness or problem based on movement, to Dr. Andrew Clarke's Equine Studies Laboratory at the University Of Melbourne.

At the Equine Centre at Werribee, Australia, Clarke uses a system of dual cameras to record simultaneously each phase of a running horse's stride from the front and the side. These cameras can record up to 500 frames of film per second and advanced software then creates a three-dimensional analysis that can "more precisely evaluate lameness, gait abnormalities and specialized foot care and shoeing requirements," according to Clarke.

Seeing is believing, so there is no need for subjective clinical interpretation in this more modern approach to gait analysis.

Applying mathematics

Dr. Sion E. M. Lawson is the lead scientist for Horse Biomechanics, a company that specializes in the evaluation of equine motion. Lawson, who has a doctorate in biomechanics from Oxford University, explains that "Biomechanics is the study of the forces acting on a biological system and is the math behind the movement."

To evaluate equine kinetics, Lawson's company uses a method of placing reflective markers on the horse and then tracking the movement of those markers with infrared cameras. "Mathematical models are then applied (to the resulting data) to provide information that can be used to analyze existing movement theories," explains Lawson, "and to plan and assess clinical treatments" (such as joint therapy and shoeing applications).

His evaluation includes a look at the balance, symmetry, power, efficiency and coordination seen in a particular horse's movement. Parameters that are measured for such an evaluation include stride length, stride frequency, center of gravity placement (a recording of where the horse carries the majority of its weight, which can help evaluate equine athletes that may jump or spin), quality of movement in joint angles and hoof placements (which provides information relating to the potential for future arthritis or performance-stress injuries) and angular momentum on the ground and in the air.

Evaluation of this type of kinetic information quickly turns mathematic, but has allowed veterinary researchers to evaluate objectively the forces on all parts of the leg, joints and hoof, as well as on specific tendons and ligaments.

The results have both an academic appeal and a practical application. A look at what we now know about heel wedges, for instance, will illustrate newer biomechanical information put to clinical use.

Heel wedges have long been used to raise the horse's heel and reduce the pull or forces on the deep digital flexor tendon (DDF). Dr. Stephen O'Grady of Northern Virginia Equine addressed the use of heel wedges in a presentation at the 2006 American Association of Equine Practitioners meeting in San Antonio. "Elevation of the heels," he explained, "induces flexion of the distal interphalangeal joint, decreases tension in the DDF tendon, reduces pressure applied to the navicular bone and reduces stress on the hoof capsule."

The kinematic models, motion-capture data and force-gauge analysis allow researchers now to make these determinations and to provide objective proof to what had, until recently, been clinical supposition.

Correcting wrong practices

This same objective analysis also has shown some practices that have been in use for years to be untrue, unfounded and potentially detrimental to the horse.

Heel wedges or heel support pads often have been used by farriers and veterinarians for the treatment of acute tendonitis. Dr. Liduin Meershoek and a group of collaborative researchers at the Faculty of Veterinary Medicine at Utrecht University in the Netherlands performed a study using force-plate testing and kinematic data to evaluate the use of heel wedges following induced superficial digital flexor (SDF) tendonitis.

Contrary to established thinking, Meersoek's group found that forces in the SDF increased in both the affected limb and the compensatory limb following application of heel wedges to both limbs. "The increase in SDF force in the compensating forelimb of horses with unilateral SDF tendonitis may explain the high secondary injury rate in this tendon," Meersoek concluded.

These researchers went further to suggest that "the lack of decrease of SDF force in either limb after the application of heel wedges suggests that heel wedges are not beneficial in horses with SSDF tendonitis and they may exacerbate the existing lesion."

Another popularly held belief is that rolling, squaring or "rockering" the toe of a horse's shoe will assist in limb movement, allowing the horse to "break over" more easily and get the foot off the ground. Shoeing in this way has long been used to reduce the forces on the interphalangeal joints in conditions such as ringbone. The speeding up of foot movement also has played a part in shoeing for tripping, overreaching and forging horses.

However, more recent research that actually measures the biomechanics of equine foot movement and the forces within the hoof have shown that this time-tested concept of rolling and squaring toes does not do what we thought it was doing.

Reporting in 1991, Dr. Hilary Clayton and other researchers found that rocker toes, rolled toes or square-toed shoes did not significantly alter break-over duration (the time it took for the hoof to leave the ground once the horse had initiated forward motion) as compared to regular plain steel shoes on the same horses.

Dr. M.A. Willemen, also of the Faculty of Veterinary Medicine at Utrecht University, further showed that the flight arc of the hoof was unaffected by rolling the toe of the shoe.

Subject for further debate

Many clinicians and farriers, however, would argue that over the years horses have improved their motion and been helped by rolled or squared toes. This may in fact be true and it will be up to continuing science and research to determine just what rolling a toe does, because — at 500 frames per second — we now know that it does not do what we thought it did.

Dr. M. C. Van Heel of the Derona Equine Performance Lab at Utrecht University has shown that forces on the pastern joint were reduced nearly 14 percent with the use of a rolled toe.

It may be that explanation for some shoeing practices and future research will be needed to separate factual biomechanics from previously held beliefs about equine motion.

More advanced computer programs will better enable veterinary researchers to do the math behind complex motion in the leg and foot and to further sort out cause and effect for shoes, pads and various conformational and pathological conditions in the horse.

In 1898, Dr. Dollar wrote, "The production of a good shoe demands intelligence, skill in the use of tools and the ability to measure accurately with the eye."

He added that "the farrier who desires to excel must possess and constantly apply a knowledge of the formation and functions of the foot."

While that all remains true, it must now be added that both farriers and veterinarians must also be able to embrace new research showing us how horses actually move and to use this new information to update ideas and clinical applications.

Dr. Marcella is an equine practitioner in Canton, Ga.