In ovo threonine administration and early feeding strategies modulate oxidative stress responses and liver metabolism in ducks subjected to post-hatch feed deprivation.

Early post-hatch development represents a critical physiological period during which nutritional interventions may influence metabolic adaptation, oxidative balance, and tissue development in poultry. This study investigated the effects of in ovo threonine (Thr) administration and post-hatch Hydrogel® supplementation, with or without Thr, on growth performance, oxidative status, antioxidant-related gene expression, hematological parameters, and liver histology in ducks subjected to delayed feed access. A total of 606 fertilized duck eggs were randomly assigned to seven experimental treatments, including immediately fed controls and groups exposed to a 36 h post-hatch feed deprivation period. Relative expression of Nrf2 and GPX1 was evaluated at hatch and after feed deprivation using quantitative PCR. Growth performance, FRAP, MDA, leukocyte profiles, and liver histopathology were also assessed. Delayed feed access significantly reduced early growth performance (p < 0.05), whereas partial compensatory growth was observed later in the rearing period. Oxidative status was also significantly affected, as reflected by altered FRAP and MDA values (p < 0.05). The highest antioxidant capacity was observed in the immediately fed saline-injected control and in ovo threonine-treated groups, while increased lipid peroxidation was detected in several delayed-fed treatments. Nrf2 expression generally decreased after feed deprivation, whereas GPX1 expression showed a more variable response pattern among treatments and sampling times. Histological evaluation revealed significant temporal changes in hepatic fat accumulation, hydropic degeneration, and lymphocytic infiltration (p < 0.05). Feed deprivation was associated with increased inflammatory and degenerative liver alterations at later sampling points. Overall, delayed post-hatch feeding induced marked oxidative and metabolic disturbances in ducks, while early nutritional interventions only partially alleviated the negative physiological effects of feed deprivation.