CHANGES IN THE 3RD METACARPAL BONE AND FREQUENCY OF BONE INJURIES IN YOUNG QUARTER HORSES DURING RACE TRAINING - OBSERVATIONS AND THEORETICAL CONSIDERATIONS

Fifty-three Quarter Horses were put into race-training at 18 mo of age . Changes in the third metacarpal were monitored by radiographic densi tometry initially at 83 days prior to the commencement of training and at days 0, 62, 104 and 244 of training. A normal increase in density of the third metacarpal due to growth and mineralization was seen from the first set of radiographs until the horses began training at day 0 (P < .001). Bone density then decreased to day 62 (P < .001), remaine d low through day 104 before it began to increase to day 244 (P < .005 ). Differences in the most optically dense portion of each cortex of t he third metacarpal were compared in horses completing the study witho ut injury and those sustaining a bone-related injury. Horses experienc ed fewer injuries when they had greater cortical mass in the lateral ( P < .05) and medial (P < .1) aspects of the third metacarpal, relative to the palmar aspect, at the commencement of training.