THE ABILITY TO ADVANCE THE ONSET OF THE BREEDING SEASON IN HORSES IS A VALUABLE TOOL FOR BREEDERS. THE DESIRE TO REPRODUCE HORSES WITH SUPERIOR GENETICS THAT CORRESPOND WITH UTILITY AND LONGEVITY, ESPECIALLY ON THE FARM, HAS CREATED A NEED FOR SUCCESSFUL AND SPECIALIZED BREEDING PRACTICES. IT IS THE GOAL OF MANY BREEDERS TO INDUCE EARLY OVULATION FOR THE PURPOSES OF HAVING EARLY FOALS AS WELL AS INCREASE THE NUMBER OF BREEDING OPPORTUNITIES SHOULD THE MARE NOT CONCEIVE. STIMULATING THE HORMONE, PROLACTIN, DURING THE NON-BREEDING SEASON HAS ADVANCED THE ONSET OF THE BREEDING SEASON BY APPROXIMATELY 60 DAYS IN MOST MARES. EXACTLY HOW PROLACTIN STIMULATES THE OVARY HAS YET TO BE IDENTIFIED. IT IS THE GOAL OF THIS PROJECT TO DETERMINE WHAT CHANGES OCCUR IN THE OVARY AFTER TREATMENT WITH PROLACTIN. WE EXPECT THAT MANY GENES ASSOCIATED WITH GROWTH OF THE EGG AND THE CELLS SURROUNDING THE EGG WILL BE TURNED ON IN RESPONSE TO PROLACTIN. SUCCESSFUL IDENTIFICATION OF A ROLE FOR PROLACTIN IN THEEQUINE OVARY WILL ENHANCE BOTH NATURAL BREEDING PRACTICES AS WELL AS EMBRYO PRODUCTION TECHNIQUES COMMONLY USED IN THE INDUSTRY.