<b>Neuroendocrine and Transgenerational Effects of Heat Stress and Photoperiodic Regulation in Poultry</b>

<p dir="ltr">This dissertation investigated the effects of heat stress (HS), nutritional strategy, and photoperiod on the physiology, behavior of breeder ducks and their offspring. In Chapter 3, chronic HS altered intestinal morphology and neuropeptide expression in a sex-dependent manner suggesting differential adaptive responses between hens and drakes. Chapter 4 showed that a high-carotenoid orange corn (OC) diet alleviated HS-induced impairments in fertility, welfare, and egg quality, likely through antioxidative and hormonal mechanisms. Building on this, Chapter 5 revealed sex-specific differences in antioxidant capacity and neuromodulation under HS, where OC diet helped stabilize dopaminergic and serotonergic turnover which indicates its role in behavioral regulation. Chapter 6 extended these findings across generations, showing that offspring of heat-stressed parents exhibited heightened stress and compromised growth, while parental OC intake mitigated glucocorticoid responses and improved behavioral responses potentially through maternal carotenoid transfer and epigenetic modifications. In Chapter 7, photostimulation (PS) was compared with continuous 24-hour light, and the result showed that while 24h lighting increased egg production, PS improved egg quality and reduced fear responses regulating reproductive hormone secretion and egg formation process. Chapter 8 explored underlying mechanisms of lighting treatment, showing that deep brain photoreceptors were differentially expressed by sex and treatment and linked photoperiodic perception to reproductive hormone regulation through gonadotropin releasing hormone and gonadotropin inhibiting hormone. In conclusion, these studies showed that HS exerts immediate and transgenerational effects on duck performance and welfare, while carotenoid-rich diets can mitigate some of these impacts. Further, PS lighting schedules may be more effective in improving performance and behavior compared to conventional 24h light. This highlights high-carotenoid OC supplementation as a promising strategy to enhance stress resilience under HS while PS may be a better alternative to conventional 24-hour lighting for optimizing performance and behavior of breeder ducks.</p>