Dietary arginine modulates egg production and mTOR signalling pathway gene expression in adult Japanese quail (Coturnix japonica)

• Body and egg mass were unaffected by 25% arginine restriction or supplementation. • Arginine supplementation increased hen-day egg production percentage. • Arginine restriction downregulated MTOR, GH, IGF1 , and lipid synthesis genes. • GH and FASN appeared as central nodes under arginine supplementation Arginine, an essential amino acid in birds, plays a central role in growth and reproduction. Regulation of the mechanistic target of rapamycin (mTOR) signalling pathway is among its key functions. This study examined how dietary arginine affects reproductive performance, body mass, and hepatic gene expression in adult female Japanese quail ( Coturnix japonica ). A total of 81 quails were randomly assigned to one of the three dietary treatments for 14 days: a diet containing 1.26% arginine (control), 0.945% arginine (restricted), and 1.575% arginine (supplemented). Body mass, hen-day egg production (HDEP), and egg mass were recorded, and liver samples were analysed using qPCR for mTOR signalling pathway-related genes. Arginine supplementation significantly increased HDEP, whereas neither restriction nor supplementation altered body mass or egg mass. Arginine restriction downregulated the expression of MTOR, IGF1, GHR, FASN, ATG5, ATG9A, SOD1 , and SOD2 genes. In contrast, supplementation upregulated ATG5 but downregulated SOD2 . Network analysis revealed treatment-dependent shifts: under restriction, SOD2 functioned as a key bridge despite reduced expression, whereas under supplementation, centrality shifted to GHR and FASN , indicating enhanced growth and lipogenic activity. Overall, dietary arginine reshaped the molecular structure of the mTOR pathway without affecting somatic maintenance, instead favouring reproductive output. These findings suggest that dietary arginine regulates egg production and gene expression in the mTOR signalling pathway in adult Japanese quail.