33rd Annual Scientific Meeting proceedings

Introduction
The evaluation of horses on the circle is an important part of every lameness examination. Reliable thresholds for head and pelvic vertical displacement values for trotting of clinically lame horses on circular path and on different surfaces have yet to be defined.

Materials and Methods
Fifty-five sound and fourty naturally lame horses were trotted under field conditions on hard surface on a straight line and lunged on both directions on soft and hard surfaces. Vertical displacement values for the head on different diagonals were quantified using a commercial gait analysis system. A receiver operating characteristic (ROC) analysis was performed to define threshold ranges to reliably differentiate sound from lame horses.

Results
Lame horses trotting on a straight line in hard ground showed an average head movement asymmetry between both diagonals of 6,5-8,5 mm. For lunging at the trot on hard and soft grounds a measured head movement asymmetry between 11,5 and 12,5 mm was consistent in lame horses. This was also detectable when differentiating between the position of the lame extremity either on the inner or outer circle.

Discussion
The threshold range in lame horses for the vertical asymmetry displacement values of the head for hard ground straight line is in agreement with the commonly reported thresholds in different studies and suggested by the manufacturer. However, when lunged these values were considerably higher. Horses in this study had different sources of lameness and were being observed under real field conditions.