Farriers must understand biomechanics and the forces at work in a horse’s hooves to best make appropriate trimming and shoeing decisions.
During the 2017 International Hoof-Care Summit, held Jan. 24-27, in Cincinnati, Ohio, Jenny Hagen, PhD, professor and researcher at Leipzig University’s Institute of Veterinary Anatomy, in Germany, explained how farriers can help horses move better using trimming and shoeing techniques.
A horse’s stride goes through two phases:
- The nonweight-bearing swing phase; and
- The stance phase, when the hoof is in contact with the ground.
Stance is further divided into three phases:
- Landing, which starts with the initial ground contact;
- Midstance, when the horse’s body is directly over the supporting limb and experiences the greatest ground reaction forces (which are exerted by the ground on the horse); and
- Breakover, which is the process of the heels lifting off the ground, rolling over the toe, and the toe leaving the ground.
Hagen has been studying the horse’s stance phase, because trimming and shoeing can directly affect the forces on the hoof and limb during this phase.
Farriers can only impact the swing phase indirectly, she said.
“All biomechanics and all strains affecting tendons, ligaments, and joints have differences depending on the stage of the stance phase,” said Hagen, adding that the center of force (also referred to as center of pressure, where all forces become equal) also changes based on the phase.
In their recent study, Hagen and colleagues collected data from 75 sound Warmbloods using an inexpensive mobile sensor system called Tekscan, which measures pressure across the various parts of the hoof. The resulting images and video revealed pressure distribution and hoof-ground contact in the stance phase, which could allow veterinarians and farriers to identify where hoof problems are located.
Hagen and her team discovered the following:
Initial Contact: How the hoof first impacted the ground varied greatly. The most common landing patterns were plane landing (all parts of the hoof contacting the ground simultaneously, which occurred in 35-42% of cases) and lateral landing (when the outer side of the hoof landed first, occurring in 35-40% of cases). Toe-first landings accounted for 15% of the cases. Medial (the inner side of the hoof landed first) and heel landings occurred at 2% and 2-3%, respectively. She noted a weak correlation between initial contact and mediolateral (side-to-side) load distribution.
Midstance: The lateral hoof side was most affected by force during this phase.
Breakover: Breakover varied horse to horse, but more cases showed pressure on the lateral aspect of the toe than other parts of the hoof.
Effects of Trimming and Shoeing
During trimming, a farrier tries to facilitate breakover and optimize the initial contact and hoof load during midstance, although it’s often difficult to improve all these aspects, said Hagen.
“If you would like to change the initial contact, gait pattern, or the stance phase of the horse, you need to aim specifically for it,” said Hagen. “You can’t just trim statically or geometrically (to the shape of the horse’s foot). You really have to check with the functional things like the walk and how the horse is moving.”
Changing how a hoof initially contacts the ground also often influences load distribution during the midstance phase, Hagen said. For each individual case, farriers must judge whether correcting of the initial contact of the hoof toward a plane landing outweighs the disadvantage of an unequal loading during the midstance phase, when the strongest forces affect the limb, she added.
While farriers can trim to change the center of force more easily in the dorsopalmar (toward the heel) then mediolateral (middle) position, it’s difficult for the farrier to use trimming to change the location of the individual breakover.
Shoes’ Impact on Stride
Farriers can also impact the horse’s stride by changing shoe weight, height, and surface. Each horse’s hoof-ground contact is different, and the effect of trimming and shoeing depends on the stage of the stance phase, posture and limb conformation, management, and manufacturing of the shoes.
“With the application of modified horseshoes, such as bar shoes, open toe shoes, or other surface modifications, specific regions of the hoof can be directly relieved to support the recovery of diseased parts of the hoof,” said Hagen.
While farriers can apply modified horseshoes to adjust initial contact and facilitate breakover, they shouldn’t use them if the result is instability during motion, especially with wedges, studs, or rocker shoes, Hagen said. She added that wedges put pressure on the heels, which can have negative effects long-term on hoof growth and shape, especially if a horse tends toward underrun heels. If a farrier needs to use wedges, Hagen recommended using long wedges made of soft material.
Hagen stressed that farriers shouldn’t rely on orthopedic shoes long-term. Just as people take antibiotics for a specified amount of time to treat a specific illness, a farrier would only use an orthopedic shoe temporarily to correct a specific problem. These shoes can affect the pressure distribution on the hoof capsule, leading to shoeing intolerance or other problems, she cautioned.