Researchers measured the load distribution under the feet of horses in an experiment to determine whether differences in the hoof wall angle between front legs delivered different readings.
They found no differences of significance that could be put down to the asymmetry, but reported that the method they used delivered highly consistent and repeatable results, suggesting it could be used to detect early signs of lameness.
Ground reaction forces in sound horses with asymmetric hooves are known to generate differences in the horizontal braking force and relative timing of the break-over in the front legs.
The center of pressure (COP) path, they said, quantified the dynamic load distribution under the hoof in a moving horse. The COP position is the net output variable of the interaction between all forces and torques in a limb.
Researchers Sandra Nauwelaerts, Sarah Jane Hobbs and Willem Back wanted to determine if differences in the hoof wall angle between front legs created asymmetry in the COP path between limbs.
They used 31 visually sound horses of different breeds with various degrees of dorsal hoof wall asymmetry, measured relative to the ground from the toe towards the coronet. Twenty were shod and 11 were unshod.
The horses were trotted three times over a pressure mat, with the COP path determined by a Qualisys motion analysis system consisting of eight high-speed cameras. Pressures underneath the hooves were measured using Gait Scientific Software that captured data from a Footscan 3-D 1 m-system.
Video footage was synchronized with the pressure data.
The researchers then looked for any relationship between left and right COP paths and the degree of asymmetry.
The study team, writing in the open-access peer-reviewed journal PLOS ONE, said some patterns were found between COP path and the dorsal wall angle. However, any asymmetry in the dorsal wall angle did not necessarily result in asymmetry in the COP path and the same could be said for symmetry.
However, the system delivered highly repeatable and unique results for each limb.
“This method is a highly sensitive method to quantify the net result of the interaction between all of the forces and torques that occur in the limb and its inertial properties,” they said.
Changes in motor control, muscle force, inertial properties, kinematics and kinetics could potentially be picked up at an early stage using this method, they added, saying it could be used as an early detection method for musculoskeletal changes.
Discussing their findings, the study team said the horses used in the study had hoof angles of between 41 and 69 degrees. Forelimbs have been reported to ideally have angles between 45 and 50 degrees, but experimental work has reported average angles of around 50.
“This means our data included ‘normal’ hoof angles as well as low (flat) and steep (upright) ones,” they noted.
“We found systematic differences between left and right across all horses (symmetric and asymmetric together).
“It has been reported that left hooves are usually larger, but even when this is corrected for the differences remain (albeit a slight shift).
“This systematic difference might be due to laterality, differences in conformation other than dorsal wall angle, difference in limb strength or muscle development, and differences in limb placement.”
They continued: “Many shapes of COP paths are possible in sound horses, but they are unique to the limb and the individual.
“We could not detect any clear patterns of COP path shape with dorsal wall angle.”
Since the COP path was the net result of numerous variables, it was hard to theoretically predict what the optimal COP path for a given individual would be.
“However, because of the consistency in the patterns, we suggest this method is so sensitive it could provide an early detection method for musculoskeletal issues when COP path shape is followed up through time.”
However, any pattern of change over time still needed to be investigated to ensure the repeatability of the COP path remained as high over time as it was within one day.
“If it is not repeatable, the technique might still be applicable if the changes over time themselves are repeatable.”
Further research was needed to assess a group of horses over time.
Nauwelaerts is with the University of Antwerp in Belgium; Hobbs is with the University of Central Lancashire in England; and Back is with the Utrecht University in the Netherlands.
Nauwelaerts S, Hobbs SJ, Back W (2017) A horse’s locomotor signature: COP path determined by the individual limb. PLoS ONE 12(2): e0167477. doi:10.1371/journal.pone.0167477