There is no mass-market board game titled "Horse-opoly." Likely possibilities:
Rules = standard Monopoly with horse-themed properties (breeds, tack, stables), "Hay" instead of Houses, "Barns" instead of Hotels, "Carrots" = $100, "Apples" = $50. Play time ~60–90 min. 2–6 players. Ages 8+.
Check the box for publisher: "Late for the Sky Production Co." If so, rules are Monopoly-standard with theme swaps. If homemade, ask the creator.