Long Day Breeders ((better)) -

Author: (For academic submission) Affiliation: Comparative Endocrinology & Reproductive Physiology Unit Date: April 14, 2026 Abstract Photoperiodism is a critical adaptive mechanism enabling animals to synchronize reproduction with favorable environmental conditions. Long day breeders (LDBs) are species in which increasing day length (i.e., longer light periods) stimulates the hypothalamic–pituitary–gonadal (HPG) axis, leading to gonadal recrudescence, mating, and parturition during spring and summer. This paper provides a comprehensive overview of the neuroendocrine basis of long day breeding, highlighting the roles of melatonin, thyrotropin (TSH), and gonadotropin-releasing hormone (GnRH). Comparative examples are drawn from mammals (e.g., Syrian hamster, horse) and birds (e.g., Japanese quail). Practical applications in animal agriculture, captive wildlife management, and biomedical models are discussed, alongside emerging genetic and epigenetic perspectives. Understanding long day breeders not only illuminates fundamental chronobiology but also supports climate-adaptive reproductive management.