Rhythmic light exposure during incubation enhances liver development and lipid accumulation in chicken embryos

Chicken embryos are typically incubated in complete darkness, overlooking the potential influence of rhythmic light exposure. This study aimed to investigate the effects of a 12-hour light/12-hour dark rhythmic light environment on liver development and lipid metabolism in chicken embryos, providing a foundation for regulating poultry physiology through light manipulation.

Fertile eggs were incubated under two lighting conditions: a 12 h light/12 h dark cycle (LD group) and constant darkness (DD group). Embryos or chicks were sampled at embryonic days 12 (E12), 14 (E14), 16 (E16), 18 (E18), 20 (E20), and day 1 post-hatch (D1). Body weight, liver weight, and residual yolk weight were recorded. Liver morphology and lipid accumulation were evaluated using H&E and Oil Red O staining. Hepatic levels of triglycerides (TG), total cholesterol (TC), free fatty acids, fatty acid synthase (FAS), and acetyl-CoA carboxylase (ACC) were measured. Expression of lipid metabolism-related genes was assessed by real-time quantitative polymerase chain reaction.

Embryo weight, liver weight, liver index, and residual yolk weight did not differ significantly between groups. However, liver tissues in the LD group exhibited earlier maturation of liver plate structures and increased lipid droplet accumulation. TG concentration was significantly higher at E12 and D1, TC at E12 and E18, and ACC at E12, E16, and E18 in the LD group (p<0.05). Furthermore, lipid synthesis genes (ACC, FAS, SCD1, SREBP-1c, ELOVL6) were upregulated, while lipid degradation genes (CPT1, PPARα, MTTP) were downregulated at specific embryonic stages in the LD group (p<0.05).

Rhythmic light exposure under a 12 h light/12 h dark cycle promoted liver development and lipid accumulation by modulating expression of lipid metabolism genes such as ACC, FAS, and CPT1. These findings highlight the potential of light rhythm as a strategy to optimize embryonic development and lipid metabolism in poultry.