Horse Medallion

That object is a horse brass (or horse harness medallion) featuring a horse design, which was originally used as a decorative plaque on a horse's harness.
Purpose and History
Traditional Use: Horse brasses were traditionally affixed to various parts of a horse's harness, such as the martingale (a strap running from the collar down the chest), particularly for draft and parade horses.
History: Their use dates back to ancient times, with early forms believed to be amulets to ward off evil spirits and bring good luck. They became especially popular in England during the Victorian era (mid-19th century).
Modern Use: As the use of working horses declined, these items became popular collector's items and were often repurposed as decorations in homes and pubs, Christmas tree ornaments, or jewelry.