Adaptation strategies of the Icelandic horse with Induced forelimb lameness at walk, trot and tölt

Lameness assessment in Icelandic horses is complex, likely due to their gait diversity. Therefore we aimed to describe their kinematic and temporal adaptation strategies in response to induced forelimb lameness at different gaits. Eleven clinically sound Icelandic horses were measured before and after left forelimb lameness induction (sole-pressure model). Upper body and limb kinematics were measured (Equimoves®, 500 Hz) at ridden walk, trot and tölt and in hand walk and trot, using seven IMU sensors (poll, withers, sacrum and all four limbs). Linear mixed models were used to compare the sound and lame conditions, and estimated-marginal means or percentage change were presented. Both in hand and ridden, lameness induction significantly (P<0.05) increased head vertical movement asymmetry (left – right) at walk (HDmin/ HDmax_HAND: -0.2/1.3 to -11.2/-5.9 mm, HDmin/HDmax_RIDDEN: 0.8/-1.8 to -5.4/-5.0 mm) and trot (HDmin/HDmax_HAND: -6.0/-0.6 to -22.5/-10.3 mm, HDmin/HDmax_RIDDEN: -4.0/-2.2 to -18.4/-9.1 mm). At the tölt, however, HDmin did not change (-3.8 to -2.7 mm) but HDmax increased (5.0 to 12.0 mm), though baseline variation for HDmax was substantial (confidence interval: -0.6-10.6). Furthermore, pelvis vertical movement asymmetry (PDmax) increased from -2.9 to -8.0 mm, right side advanced placement decreased (-10.7%), and right diagonal advanced placement increased (9.0%). Kinematic adaptations to forelimb lameness at tölt were less evident than those at walk or trot. Therefore, classic forelimb lameness metrics, such as vertical head and withers movement asymmetry, did not provide valuable information. Instead, vertical pelvic movement asymmetry and some limb parameters were helpful in forelimb lameness detection at tölt.