The Connectivity and Histological Structure of the Equine Ergot-A Preliminary Study

The equine ergot is a dense fibrous cushion on the palmar aspect of the fetlock joint that often manifests externally as a variably sized callosity. The study presented here investigated the macroscopic structure, connectivity, and the histological properties of the ergot to elucidate its functional significance. Distal forelimbs, obtained from 18 horses euthanized for reasons unassociated with this study, were dissected using photography and videography to record the observed connections. In an additional five limbs, a section of the ergot was dissected and prepared for histological and immunohistochemical staining to examine its tissue structure and innervation. The ergot tissue was found to be intimately associated with the overlying skin and to have a strong attachment point at its center to the underlying fetlock palmar annular ligament. In cases where increased epidermal growth was present, it was histologically identical to the equine chestnut. Nerve fibers and Ruffini endings were observed in both the ergot tissue and its derived ligaments. The expansive connectivity of the ergot and its associated fascia suggest that it has a role in integrating the structures comprising the distal forelimb and in distributing tension among these structures. In addition, the presence of Ruffini endings suggests that the ergot ligament may have a mechanoreceptive role that is important in the positioning of distal limb joints.