Determining Objective Parameters to Assess Gait Quality in Franches-Montagnes Horses for Ground Coverage and Over-Tracking - Part 2: At Trot.

In gait quality assessments of horses, stride length (SL) is visually associated with spectacular movements of the front limbs, and described as ground coverage, while the movement of the hind limb under the body is supposedly essential to a longer over-tracking distance (OTD). To identify movement patterns with strong associations to SL and OTD, limb and body kinematics of 24 Franches-Montagnes (FM) stallions were measured with 3D optical motion capture (OMC) on a treadmill during an incremental speed test at trot (3.3-6.5 m/s). These measurements were correlated to the scores of ground coverage and over-tracking from six breeding experts. The amount of explained variance of parameters on SL and OTD were estimated using linear mixed-effect models in two models: a full model with all parameters measurable with OMC, and a reduced model with a subset of parameters measurable with inertial measurement units (IMUs). The front limb stance duration (16%) and OTD (7%) measured with OMC, or the OMC parameters front limb stance duration (24%) and suspension duration (14%) measurable with IMUs explained most variance in SL. However, four of six breeding experts were also significantly correlated (r>|0.41|) to front limb protraction angle. OTD variance was explained with OMC parameters suspension duration (10%) and hind limb contralateral pro-retraction angles (9%) or IMU-measurable parameters suspension duration (20%) and maximal pelvis pitch (5%). Four experts' scores for over-tracking were correlated to suspension duration. These results underscore the need for precise definitions of gait quality traits.

Reliable and clinically applicable gait event classification using upper body motion in walking and trotting horses.

Objectively assessing horse movement symmetry as an adjunctive to the routine lameness evaluation is on the rise with several commercially available systems on the market. Prerequisites for quantifying such symmetries include knowledge of the gait and gait events, such as hoof to ground contact patterns over consecutive strides. Extracting this information in a robust and reliable way is essential to accurately calculate many kinematic variables commonly used in the field. In this study, optical motion capture was used to measure 222 horses of various breeds, performing a total of 82 664 steps in walk and trot under different conditions, including soft, hard and treadmill surfaces as well as moving on a straight line and in circles. Features were extracted from the pelvis and withers vertical movement and from pelvic rotations. The features were then used in a quadratic discriminant analysis to classify gait and to detect if the left/right hind limb was in contact with the ground on a step by step basis. The predictive model achieved 99.98% accuracy on the test data of 120 horses and 21 845 steps, all measured under clinical conditions. One of the benefits of the proposed method is that it does not require the use of limb kinematics making it especially suited for clinical applications where ease of use and minimal error intervention are a priority. Future research could investigate the extension of this functionality to classify other gaits and validating the use of the algorithm for inertial measurement units.

Should We Agree to Disagree? An Evaluation of the Inter-Rater Reliability of Gait Quality Traits in Franches-Montagnes Stallions.

Gait quality, that is, the way horses move according to functional and aesthetic principles, englobes many traits that are scored by experts during breeding competitions. The experts can score a trait on a subjective valuating (SV) scale or on a linear profiling (LP) scale representing the biological extremes of the population. However, the reliability of the appraisal of gait quality traits has not been extensively evaluated. In this study, seven breed experts appraised the walk and trot quality of 24 Franches-Montagnes stallions presented in hand on a sand track. Inter-rater reliabilities of six traits (five SV and one LP) at the walk and eight traits (five SV and three LP) at the trot were estimated with intraclass correlation coefficients (ICCs). The inter-rater reliabilities were poor (ICC < 0.50). The scale anchoring varied between experts, and the variance of scores was low. There were no systematic differences in inter-rater reliability between LP and SV traits. Future studies should determine whether the inter-rater reliabilities may be increased by a more precise definition of the scores within each trait to improve the absolute agreement between experts, by a more uniform scale anchoring between experts, and by decreasing the number of scale items. However, considering the inherent limitations of the human eye in observing high-speed movement, the use of a field-applicable kinematic measurement system may support breeding experts in the appraisal of gait quality traits in the future.