Green light and intermittent lighting modulate testicular gonadotropin inhibitory hormone without central or morphological effects in broiler chickens

Environmental factors, especially light duration and wavelength (colour), affect reproductive physiology in broilers. In birds, light is perceived especially by extraretinal photoreceptors in the brain, including the hy pothalamus, which regulates reproductive function. Gonadotropin-inhibitory hormone (GnIH), expressed in both the hypothalamus and gonads, suppresses gonadotropin release and modulates reproductive activity. Its expression is influenced by photoperiod and light colour. Rooster fertility is economically important, as one male can inseminate many females. This study investigated how green light and intermittent lighting affect GnIH levels and testicular development in prepubertal broiler males. 288 one-day-old male commer cial broilers (Ross-308) were divided into four groups (n=12) and exposed to: Group I, 18 hours light - 6 hours dark (18L:6D) with white light; Group II, 18L:6D with green light; Group III, 17L:3D:1L:3D with white light; and Group IV, 17L:3D:1L:3D with green light. The study was conducted in four identical ex perimental rooms, each consisting of six pens (replicates). Two male broilers were randomly selected from each pen. A total of 48 chickens, 2 males from each pen (replicate group), were randomly selected for analysis. After 42 days under standard conditions, GnIH levels were measured in the hypothalamus and testes via ELISA. Testicular development was assessed histologically by evaluating seminiferous tubule diameter and epithelial height. Results showed that intermittent lighting and green light significantly in creased testicular GnIH levels but had no effect on hypothalamic GnIH. The most pronounced increase in testicular GnIH was observed in Group IV, which received both intermittent lighting and green light. No significant differences were observed in testicular morphology. These findings suggest that intermittent lighting and green light may selectively influence gonadal GnIH levels without affecting central GnIH or morphology, offering insight into how lighting strategies may be optimized in poultry production.