The original ceramic Hagen-Renaker mold, #24 Mini Thoroughbred Mare
20, was sculpted by Maureen Love Calvert, and leased from the company by Breyer for production in plastic. The Thoroughbred Mare mold was released in 1976 and was discontinued along with the other Generation One molds at the end of 2005.
I love it when things divide out evenly - Breyer released seven regular runs and seven special runs on this mold, putting her in a tie with Citation for the third least used mold.