Phytochemicals and reproductive function in wild female Phayre's leaf monkeys (Trachypithecus phayrei crepusculus)

►Fecal progestins (fP) were high in female leaf monkeys when Vitex fruits and leaves were abundant. ►During high progestin periods, females had longer menstrual cycles and follicular phases. ►When ovulations did occur in the high progestin period, females were more likely to conceive. ►However, conceptions were also more likely when females were in positive energy balance. ►Results consistent with both a phytosteroid and energetic effect on female reproduction.