Sheep,beginning its breeding season in the autumn ,is considered to be a short day breeder.It is generally postulated that the pineal hormone melatonin synchronizes ovine reproductive cycle with environmental photoperiod through neuroendocrine changes in the hypothalamo pituitary gonadal axis.A lot of recent studies demonstrated that melatonin receptor was involved in the photoperiodism.This paper,based on the research progress in ecology,neuroendocrinology and molecular biology,reviews the regulative ef...