摘要：Seven horses were exercised five days a week for 12 months at different gaits on a treadmill, and eight horses were pastured freely in a paddock without any training programs. They were 60 days of age at the beginning of the experiment. We compared the number of C cells in the thyroid, ultrastructure of chief cells in the parathyroid and radiography of the third metatarsal bone of the training group with the control group. In the training group, the number of C cells was not increased and chief cells were not in a phase of secretion. In addition, the bone mineral content and the cortical area did not show high values. We considered that an additional exercise used in this study had suppressive effects on the thyroid and parathyroid. Our results also suggest an additional and/or intense exercise in early stage of life (foal to weanling) may have an adverse effect on bone growth and metabolism.
