Changes due to age in the kinematics of trotting Andalusian foals.

The purpose of this study was to evaluate the effect of growth on biokinematic characteristics at the trot in a group of 9 Andalusian foals from age 12 to 36 months in order to identify which stride variables change or remain invariable. Biokinematic analysis was performed by using a computer-assisted videography system (25 Hz frame rate). An increase in stride length as well as the fore- and hindlimb stride duration was found. A tendency to increase flexion of the shoulder, elbow and carpal joints was observed while the forelimb fetlock increased its maximal extension. In the hindlimb, most of the differences were exhibited by the hip and stifle joints, which showed a tendency to a lesser flexion with age. However, at landing the extension was bigger. The hindlimb fetlock extended more in older foals, whereas flexion decreased. Significant differences in the maximal extension and flexion instants in the forelimb joints were not detected (except in the elbow joint). The same was found in the angular range of motion (ARM) of the scapula inclination and the shoulder and forelimb fetlock joints. Differences in retraction-protraction angles in both the fore- and hindlimbs were very slight, and ARM values for these parameters were similar in all age groups. It can be concluded that Andalusian horses modified their locomotor pattern at the trot between age 12 and 36 months, particularly up to 24 months, by increasing stride length as well as shoulder, elbow and carpus flexion, while hip and stifle flexion decreased and hindlimb joints were more extended during the stance phase. One of the most striking features was that maximal retraction and protraction angles did not change in foals age 12-36 months in either fore- or hindlimbs. These results could be useful for the prediction of some kinematic parameters of mature horses from data obtained at younger ages.