Zearalenone is a mycotoxin that has been found in Fusarium and has estrogenic activities.¹ It binds to human estrogen receptor α (ERα) and ERβ (IC50s = 9 and 5.8 nM, respectively).² Zearalenone induces precocious development of mammary tissues in young female pigs and prepucial enlargement in young male pigs.³ Zearalenone (1.5-5 mg/kg of diet) induces hyperestrogenism in pigs. It also induces degeneration of meiotic chromatin in oocytes and reduces fertility in pigs when administered at a dose of 200 µg/kg.⁴ Zearalenone has been found as a contaminant in wheat, maize, and barley and livestock feeds.^3,4