Adaptation strategies of Icelandic horses with induced transient hindlimb lameness at walk, trot and tölt

BACKGROUND: Icelandic horses are valued for their additional gaits, but assessing lameness in this breed can be challenging. Pelvic (P) vertical movement asymmetries, differences (D) in minimum (min)/maximum (max) position, are used to quantify impact (PDmin) and push-off (PDmax) hindlimb lameness during the trot, but no established parameters exist for detecting hindlimb lameness in other gaits.

OBJECTIVE: To evaluate temporal stride parameters and upper-body movement asymmetry after transient hindlimb lameness induction in walk, trot and tölt.

STUDY DESIGN: In vivo experiment.

METHODS: Eleven Icelandic horses were measured before and after hindlimb lameness was induced (sole pressure). Vertical movement asymmetry of Head (H)/Pelvis (HDmin/HDmax/PDmin/PDmax) and hip-hike were measured during ridden walk, sitting trot and tölt as well as in-hand walk and trot, using an inertial measurement unit system. Linear mixed models compared sound and lame conditions within each gait, and differences in estimated marginal means (mm) between conditions are presented, with significance set at p < 0.05.

RESULTS: Lameness induction significantly increased PDmin asymmetry in all gaits except walk in-hand: walk (PDmin ridden: 5.07), trot (PDmin hand: 10.72, PDmin ridden: 9.85) and tölt (PDmin ridden: 4.88). However, PDmax increased only for trot in-hand (PDmax hand: 4.80). Hip-hike increased on the lame limb side at trot (hip-hike hand: 20.90, hip-hike ridden: 10.81) and tölt (hip-hike ridden: 4.28).

MAIN LIMITATIONS: Findings need verification in clinically lame Icelandic horses with varying diagnoses and lameness severity.

CONCLUSION: PDmin and hip-hike appear to be effective parameters for detecting mild hoof-associated hindlimb lameness in Icelandic horses when trotting in-hand or ridden. At walk or tölt under saddle, only slight PDmin changes were observed, likely due to lower limb loading in those gaits and the pelvic minimum position associating with different loading stages throughout the stride cycle for walking and running gaits. These findings suggest trot is the preferred gait for assessing mild hindlimb lameness in Icelandic horses.