The effect of exercise on the distribution and manifestation of osteochondrotic lesions in the Warmblood foal.

Osteochondrosis (OC) in the horse has been defined as a disturbance in the process of endochondral ossification which is of multifactorial origin, becoming evident in a large number of joints. Exercise is one of the environmental factors that may influence the clinical manifestation of the disorder, but has never been thoroughly investigated. In this study we investigated the influence of exercise during the first 5 months on the development and distribution of OC lesions in foals of age 5 and 11 months. Forty-three foals, all from sires having OC in either the femoropatellar or tibiotarsal joint, were reared to weaning at 5 months under similar conditions except for the type and amount of exercise. Fifteen foals remained at pasture, 14 were kept in box stalls and 14 foals were kept in the same box stalls but daily given an increasing number of gallop sprints. After weaning, 8 foals from each group were subjected to euthanasia. The remaining 19 animals were given identical light exercise regimen for an additional 6 months to euthanasia at 11 months. After euthanasia all major diarthrodial joints were inspected for macroscopic lesions. Histological sections were made from the lesions and from all distal tibial sagittal ridges. Lesions were scored according to severity on a scale of 0 to 4, and a total OC score per joint was calculated. In the 5 month group, lesions were found in all foals (mean number of lesions 5.5, range 1-14). Frequency was highest in the tibiotarsal (1.9 lesions/foal), the femoropatellar/femorotibial (1.0), the cervical intervertebral (1.0), and the metatarsophalangeal joints (0.6). At 11 months the prevalence of lesions had significantly decreased (mean number of lesions 3.1, range 0-7). This decrease was most evident in the femoropatellar/femorotibial joint, but was negligible in the tibiotarsal joint. Exercise did not significantly influence numbers of lesions, but at 5 months there was a tendency towards more severe lesions in the box-rested foals. In the femoropatellar/femorotibial joint, lesions were found mainly in the femoral condyles of the box-rested foals and at the lateral trochlear ridge of the femur in the trained foals. It is concluded that OC may become manifest in many joints. Many lesions regress and do not become clinically evident, making the number of horses with lesions at mature age into an underestimation of the total amount of animals that have suffered from the condition. The period during which a lesion develops and possibly regresses is limited and variable per site. Exercise at the level given in this study may have some influence on the appearance and the distribution of the lesions, but did not appear to have an aetiological role.