Discipline-associated locomotor coordination and asymmetry patterns in trained Quarter Horses: a cross-sectional study.

Overview

• This study investigated how trained Quarter Horses used in different Western riding disciplines exhibit unique patterns of locomotor coordination and asymmetry while moving in a standardized straight line.
• The research aimed to determine if these discipline-related differences in movement exist independently of lameness, and whether horse body conformation explains these differences.

Background and Objectives

• Locomotor Asymmetry in Horses: Traditionally seen as an indicator of pain or lameness, measurable asymmetries in horse gait may also occur in clinically sound animals.
• Need for Study: It has been unclear whether horses trained in distinct athletic disciplines—such as barrel racing, reining, and ranch sorting—display characteristic asymmetry patterns when moving under controlled, straight-line conditions.
• Research Goal: To examine locomotor asymmetry and vertical displacement differences in Quarter Horses from these three disciplines, and explore if physical conformation (morphometrics) relates to locomotion differences.

Methods

• Subjects: 90 adult Quarter Horses were initially recruited, with 57 retained after quality control (19 per discipline: barrel racing, reining, ranch sorting).
• Testing Conditions: Horses were evaluated walking and trotting in-hand on a straight 100-meter sandy track to standardize conditions.
• Instrumentation: ProMove-mini inertial measurement units recorded data at 200 Hz, positioned on key anatomical landmarks—head, withers, sacrum, and limbs.
• Measured Variables:
  • Vertical displacement asymmetry using Mindiff and Maxdiff at head, withers, sacrum
  • Interlimb asymmetry assessed by Symmetry Index, Asymmetry Ratio, and absolute side-to-side differences
  • Spatiotemporal, angular, and vertical acceleration variables
• Data Analysis:
  • Discipline effects tested using horse-level averaged values; gait velocity included as covariate when relevant
  • Principal component analysis (PCA) to analyze static morphometric traits
  • Elastic Net models (cross-validated) explored associations between morphometric data and locomotor variables

Key Findings

• Discipline-associated Differences:
  • Reining horses exhibited greater vertical displacement asymmetry in the head and withers compared to barrel racing horses.
  • Ranch sorting horses showed larger absolute side-to-side differences in hindlimb acceleration and range-of-motion variables than others.
  • Asymmetry patterns varied by gait (walk vs. trot) and anatomical segment, indicating complexity across locomotor features.
• Morphometric Analysis:
  • PCA of body conformation did not clearly separate horses by discipline.
  • Elastic Net models showed only moderate correlations between morphometric measures and locomotor variables (R² values between 0.35 and 0.42), implying limited predictive power.
• Interpretations:
  • Locomotor asymmetry is influenced by discipline-specific training and functional demands rather than being explained solely by physical conformation.
  • The phenomenon is multifaceted and dependent on the interaction of biomechanics, discipline, and individual movement history.

Conclusions and Implications

• Quarter Horses trained in barrel racing, reining, and ranch sorting exhibit discipline-related locomotor asymmetry patterns in standardized conditions even without signs of lameness.
• Horse body shape alone does not explain these asymmetries, indicating the importance of considering training effects and locomotor context.
• This suggests veterinary and biomechanical assessments of horse gait should factor in discipline-specific movement patterns to avoid misinterpreting natural asymmetries as pain or injury.
• Future studies might explore the effects of training, workload, and long-term musculoskeletal adaptations on gait asymmetry to enhance horse welfare and performance evaluation.