Seasonal testicular regression in Yangzhou geese: Transcriptomic evidence for an immune-reproductive trade-off during the transition from peak to shutdown egg production.

This study investigated developmental changes and the underlying molecular mechanisms in testicular tissue of Yangzhou geese during the transition from the peak production (PP) to egg production shutdown (PF) periods. We hypothesized that this transition is accompanied by a reciprocal shift in resource allocation-declining spermatogenic activity offset by enhanced immune function-reflecting an adaptive life-history trade-off in this seasonally breeding species. Five Yangzhou geese were randomly selected each during the PP (day 73) and PF (day 135) periods, based on the endogenous seasonal reproductive rhythm of this breed under standard 12L:12D production lighting. Blood samples were collected for serum biochemical and hormonal analysis, and left testicular tissues were collected for RNA sequencing (RNA-seq) and quantitative RT-PCR (qRT-PCR) validation. The results show: the Johnsen spermatogenic score and the number of mature spermatozoa were significantly higher in the PP group (P < 0.05). Serum follicle-stimulating hormone (FSH) concentration was significantly higher in the PP group than in the PF group (P < 0.05). RNA-seq identified 3605 DEGs (FDR <0.05, |log2FC| > 1); enrichment analysis (BH adj. P < 0.05) revealed significant upregulation of immune-related pathways (phagosome, hematopoietic cell lineage, complement and coagulation cascades) and downregulation of spermatogenesis-related terms (cilium movement, axonemal dynein complex assembly) in the PF group. Serum concentrations of interferon-gamma (IFN-γ) and immunoglobulin G (IgG) were also significantly elevated in the PF group (P < 0.01), and immune indices were negatively correlated with reproductive indices. These findings support an adaptive immune-reproductive trade-off during seasonal testicular regression in Yangzhou geese, advancing our understanding of resource allocation strategies in seasonally breeding poultry.