Effects of in ovo dextrose, niacin, and retinoic acid administration on embryonic metabolism, antioxidant defense, and hepatic gene expression in long-stored broiler breeder eggs.

OBJECTIVE: Prolonged storage of broiler breeder eggs may aggravate the naturally limited carbohydrate availability of the avian egg and increase oxidative pressure during late embryogenesis. This study evaluated the effects of in ovo administration of dextrose (D-glucose), niacin, and retinoic acid on embryonic metabolism, glycogen deposition, antioxidant defense, and hepatic gene expression in broiler breeder eggs stored for 14 days.

METHODS: After 14 days of storage and E18 candling, a total of 640 fertile Ross 308 hatching eggs were included in the in ovo injection phase. Experimental groups consisted of control, dextrose (DEX), niacin (NIA), retinoic acid (RA), dextrose + niacin (DEX+NIA), and two RA-containing combination groups (RA+DEX+NIA-L and RA+DEX+NIA-H). At hatch, serum biochemical parameters, serum and liver antioxidant indicators, liver and muscle glycogen concentrations, and the relative hepatic expression of genes associated with energy metabolism and redox regulation were evaluated.

RESULTS: The findings revealed two distinct yet partially complementary response patterns. DEX, NIA, and especially DEX+NIA were more consistently associated with higher serum glucose, increased liver and muscle glycogen deposition, and gene-expression patterns consistent with metabolic support. Among serum biochemical variables, glucose was the most responsive parameter and was significantly increased in the DEX, NIA, DEX+NIA, RA+DEX+NIA-L, and RA+DEX+NIA-H groups compared with the control group. In contrast, RA was more clearly associated with antioxidant regulation, showing marked upregulation of NRF2 together with a more pronounced hepatic antioxidant enzyme response, particularly in CAT and GPx activities. Overall, antioxidant modulation was more evident in liver tissue than in serum. These treatment-specific profiles suggest that the embryonic response to prolonged storage may involve more than one physiological axis.

CONCLUSION: In ovo metabolic interventions may help modulate the physiological burden imposed by prolonged egg storage, although the dominant physiological profile appears to depend on the compound administered. Under the present conditions, DEX/NIA-based treatments were more closely related to energy reserve support, whereas RA was more closely related to antioxidant defense. These findings provide a physiological basis for further studies on in ovo strategies aimed at improving resilience in long-stored broiler breeder eggs.