In ovo green light cycles (6 versus 12 hours) modulate embryonic development via hepatic gene expression and amino acid metabolism in ducks

1. While in ovo green lighting (IOL) promotes embryo growth and shortens the incubation period in meat-type ducks, photoperiod effects remain unclear. This study investigated the impact of different IOL photoperiods on embryo development, the hepatic transcriptome and amino acid metabolism.2. A total of 300 fertilised Pekin duck eggs were divided into three groups (n = 100/group) with eight replicates per group and 12–13 eggs per replicate. For the light-treated groups, green LED lamps (520–526 nm, 150 lux) were inserted into the air cells on embryonic day (ED) 9. From ED10 to ED24, eggs were subjected three treatments. 1. Control group conventional total darkness without LED implantation (CON), 6 h/day short-term lighting (STL), or 12 h/day long-term lighting (LTL), both with lights turned on at 07:00 daily. Embryo, heart and liver weights were measured on ED17 and 24, with ED24 livers collected for free amino acid, transcriptomic and PCR analyses.3. Heart and liver weights were unaffected by IOL. However, while embryo weight on ED24 was significantly higher in the LTL group, relative embryonic weight did not differ significantly. Apart from proline, IOL significantly reduced free amino acid levels in the liver, which increased in decline with longer photoperiods. Transcriptomic comparisons between the LTL and CON embryos revealed that light exposure upregulated genes related to energy, lipid and amino acid metabolism, but suppressed extracellular matrix (ECM) genes.4. The 12 h/day green IOL photoperiod altered transcriptomic signatures associated with amino acid utilisation and energy metabolism during the late stages of embryogenesis. This contributed to absolute embryonic biomass accumulation in meat-type ducks.