In this paper a novel method for automatic determination of stride phases duration in horses is assessed under field conditions from video recordings. The method uses the hoof horizontal speed and fetlock joint angle. Using 56 different video sequences of horses at hand-led slow trot in outdoors conditions and using eye-witness decisions of 4 referees, the percentage of absolute error (the sum of absolute values of the differences between referees opinion and results of the method) obtained using the unfiltered signal to determine the contact frame was 2.24 %, and to determine the rise it was 2.34 %. Using unfiltered and filtered (10 Hz) signals r2=0.787 andr 2=0.742, respectively, were obtained comparing the stance phase time obtained by the assessed method and by the referees' opinion.