Abstract: Horses commonly show asymmetries that manifest as left (L)-right (R) differences in vertical excursion of axial body segments. Moving on a circle confounds inherent individual asymmetries. Our goals were to evaluate individual and group asymmetry patterns and compare objective data with subjective impressions of side preference/laterality in horses walking on L and R circles. Unassigned: Fifteen horses walked on L and R circles unridden and ridden on long and short reins. Optical motion capture (150 Hz) tracked skin-fixed markers. Variables were trunk horizontal angle; neck-to-trunk angle; vertical range of motion (ROM) for the head, withers and sacrum; ROM for pelvic roll, pitch, and yaw; mean pelvic pitch; and ROM for hip, stifle and tarsal joints. Differences between inside and outside hind steps were determined for vertical minima and maxima of the head (HMinDiff/HMaxDiff), withers (WMinDiff/WMaxDiff) and sacrum (PMinDiff/PMaxDiff). Subjective laterality was provided by owners. Data analysis used mixed models, first without and then with subjective laterality. Iterative k-means cluster analysis was used to associate biomechanical variables with subjective laterality. Unassigned: PMaxDiff, PMinDiff and WMaxDiff indicated R limb asymmetry in both directions. WMinDiff indicated L (inside) fore asymmetry for L direction but was close to zero for R direction. Hip ROM was significantly smaller for the inside limb in both directions (L inside/outside: 16.7° . 20.6°; R: 17.8° . 19.4°). Stifle ROM was significantly larger for the inside limb in both directions (L: 43.1° . 39.0°; R: 41.9° . 40.4°). Taking the general direction effect into account the R hip and L stifle had larger ROM. Adding laterality to the models (seven horses L- . six horses R-hollow), PMaxDiff R hind asymmetry was more obvious for L-hollow horses than for R-hollow horses. L-hollow horses had greater pelvic roll ROM moving in L . R direction. L-hollow horses had smaller inside and greater outside hip joint ROM in L . R direction. R-hollow horses had a significant difference in HMinDiff between L (0 mm) and R (-14 mm) directions, indicating less head lowering at outside forelimb midstance in R direction, and larger outside tarsal ROM in R (38.6°) . L (37.4°) direction ( ≤ 0.05). The variables that agreed most frequently with subjective laterality in cluster analysis were pelvic roll ROM, followed by HMinDiff and PMaxDiff. Unassigned: Differences between horses walking in L and R directions were found both at group and individual levels, as well as evidence of associations with subjective laterality. Horses maintained more symmetric hip and stifle ROM and withers vertical motion when walking on the R circle. Findings suggest that left and right lateralised horses may not be perfect mirror images. Pelvic roll ROM emerged as a promising variable to determine laterality in walk as perceived by the rider, especially when considered together with other variables.
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This study investigates how horses display asymmetries—differences in movement between the left and right sides—when walking in circles, both ridden and unridden. Using motion analysis techniques, researchers looked for patterns in horse movements, comparing these patterns to the subjective observations of the horse’s usual direction preference. Findings suggest horses maintain different movement symmetry based on the direction they walk, and that the asymmetrical nature may not simply be the mirror image of the other side.
Methodology
Fifteen horses participated in the study, each walking in left and right-direction circles while being ridden and unridden.
Movement data was collected using optical motion capture technology, which tracked markers placed on the horse’s body.
The specific variables examined were numerous aspects of the horse’s movement, ranging from angles of the neck and trunk, to the range of motion for different parts of the body and joints.
Laterality, or the horse’s preferred side, was assessed through the subjective reporting of the horse owners.
This data was analyzed using mixed models, at first without considering reported laterality, but then including it.
A statistical method known as k-means cluster analysis was used to find associations between the biomechanical variables and subjective laterality.
Findings
The study revealed right-limb asymmetry in both walking directions for the horses, finding differences in the vertical range of motion for several body parts between the inside and outside steps of the circle.
The left forelimb showed asymmetry when walking in a left-circle direction but was nearly symmetrical when walking to the right.
Changes in the horses’ hip and stifle joints’ range of motion were seen, with the inside limb showing less hip movement and more stifle movement in both directions.
When considering the horse’s laterality, based on owner reports, it was found that these asymmetry patterns were more pronounced for horses preferring to walk in a left direction.
Conclusion
The study found that both individual horses and the group as a whole showed differences in movement symmetry based on the direction they were walking.
These asymmetries also appeared to correlate with the horse’s subjective laterality, as reported by owners.
The research concluded that horses maintain more symmetry in certain movements when walking to their preferred side. However, it was suggested that this is not a perfect mirror image of the other.
The research also identified certain movement variables that may be able to objectively determine a horse’s preferred side or laterality.
Cite This Article
APA
Egenvall A, Clayton HM, Byström A.
(2023).
Pilot study of locomotor asymmetry in horses walking in circles with and without a rider.
PeerJ, 11, e16373.
https://doi.org/10.7717/peerj.16373
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