Abstract
Fasting and refeeding protocols, which induce short-term fluctuations in nutrient and energy levels, elicit adaptive physiological responses in animals. In this study, biochemical, transcriptome and 16S rRNA sequencing techniques were used to investigate the physiological effects of fasting and refeeding on immune responses, liver gene expression, and gut microbiota composition in geese. Fasting led to a significant reduction in circulating levels of IgA and IFN-γ, while IgG, TNF-α, IL-6, and IL-10 levels remained stable. Upon refeeding, IgA and IFN-γlevels rapidly returned to baseline. RNA-Seq analysis identified 858 differentially expressed genes (DEGs) between the control and fasted groups, and 732 DEGs between the fasted and refed groups. Key regulatory genes involved in energy metabolism and lipid biosynthesis, such as CPT1A, HMGCS1, and PCK1, were upregulated during fasting, reflecting an increase in fatty acid oxidation and gluconeogenesis. Conversely, lipogenic genes, including FASN, ACSS2, ACCα, and SCD, were downregulated during fasting and upregulated during refeeding, indicating a metabolic shift from catabolic to anabolic processes. Gene Ontology (GO) and KEGG pathway enrichment analyses revealed significant involvement of the PPAR signaling, glycolysis/gluconeogenesis, and insulin signaling pathways. Additionally, 16S rRNA gene sequencing indicated that fasting increased the abundance of Bacteroidetes and Proteobacteria, while decreasing Firmicutes. Both alpha and beta diversity were significantly reduced during fasting. Functional analysis of the gut microbiota suggested a shift toward fatty acid oxidation during fasting. Correlation analysis further demonstrated that the relative abundance of Barnesiella was positively correlated with genes involved in gluconeogenesis and negatively correlated with lipid metabolism genes, such as ELOVL6 and PHGDH. This underscores the role of the gut-liver axis in regulating metabolic adaptations. These findings offer critical insights into how short-term fluctuations in nutrient availability influence immune function, metabolic regulation, and gut microbiota composition in geese. This research also provides potential strategies for optimizing poultry nutrition and health management.