The Role of Photoperiod and Melatonin in the Epigenetic and Hormonal Regulation of Seasonal Reproduction in Ruminants

Photoperiod and its associated neuroendocrine and epigenetic mechanisms play a fundamental role in the seasonal regulation of reproduction and growth in ruminants. Evidence from the reviewed studies indicates that manipulation of the light cycle-particularly through short-day photoperiod simulation or melatonin implants-enhances melatonin secretion and stimulates the hypothalamic-pituitary-gonadal axis, thereby improving estrous expression, sexual behavior, and out-of-season conception in sheep. At the molecular level, alterations in photoperiod are accompanied by extensive rearrangements in uterine microRNA regulatory networks and DNA methylation patterns within the hypothalamus, influencing pathways involved in synaptic development, thyroid signaling, circadian rhythm, cell proliferation, and apoptosis. Moreover, data show that age-related variation in ovarian activity of Barkhi sheep exerts no significant effect on fertility indices, indicating that ewe-lambs can effectively participate in reproductive cycles. In hormonal models, GnRH administration accelerates sexual maturation and enhances follicular activity, whereas gestational hyperandrogenism modulates growth and metabolic pathways in a sex-specific manner, revealing fetal sensitivity to the intrauterine environment. Beyond reproduction, a reduction in day length in Cashmere goats activates the Wnt/ß-catenin signaling pathway, stimulates growth-related hormones, and strengthens the antioxidant system, facilitating the initiation of active cashmere fiber growth. Collectively, these findings demonstrate that ambient light and its downstream hormonal and epigenetic mediators orchestrate an integrated physiological network that simultaneously governs seasonal reproduction and growth. Strategic utilization of these mechanisms may serve as an effective approach to improve reproductive efficiency, enhance livestock product quality, and optimize flock management in smallholder systems.

کلیدواژه ها:

Artificial photoperiod ، Melatonin ، Epigenetic regulation of the hypothalamus ، Seasonal reproduction in sheep and goats