We studied the microbial profiles of the duodenum, jejunum, and ileum during different developmental stages in the duck using high-throughput sequencing of the bacterial 16S rRNA gene. We also investigated the differences in the microbiota in the duodenum, jejunum, and ileum at different developmental times. A correlation analysis was performed between the most abundant bacterial genera and the development of the small intestine. An analysis of alpha diversity indicated different species richness and bacterial diversity in the different small intestinal segments and at different development times. A beta diversity analysis indicated differences in the bacterial community compositions across time. In a weighted UniFrac principal coordinates analysis, the samples clustered into two categories, 2 to 4 wk and 6 to 10 wk, in the duodenum, jejunum, and ileum. Our results show that the small intestine is predominantly populated by the phyla Firmicutes, Bacteroidetes, and Proteobacteria throughout the developmental stages of the duck. The duodenum, jejunum, and ileum shared most of the bacterial phyla and genera present, although they showed significant differences in their relative abundances in the intestinal segments and developmental stages. They shared different bacterial taxa during development times and among different segments when the intergroup differences were analyzed. The genera Bacillus, Corynebacterium 1, Lactococcus, Sphingomonas, and Haliangium correlated moderately positively with the increase in bodyweight and the lengths and weights of the duodenum, jejunum, and ileum, and these genera may be considered important markers when assessing the heath of the intestinal microbiota in ducks. This study provides a foundation upon which to extend our knowledge of the diversity and composition of the duck microbiota and a basis for further studies of the management of the small intestinal microbiota and improvements in the health and production of ducks.

Computer-assisted sperm analysis was conducted to phenotypically and genetically assess the sperm motility traits of Jinding drakes. The phenotypic evaluation revealed moderate variability across motility parameters, consistent with a polygenic inheritance pattern. Correlation analysis further demonstrated strong associations among velocity-related traits and inverse relationships between linearity and lateral head displacement metrics. Genome-wide association studies identified 15 significant single-nucleotide polymorphisms (SNPs) associated with five key sperm motility traits (straight-line velocity, curvilinear velocity, average path velocity, amplitude of lateral head displacement, and mean angular displacement) at a genome-wide threshold of p < 1 × 10⁻⁶. Notably, of these 15 SNPs, nine were concentrated on chromosome 1, indicating the presence of a genomic hotspot for regulation of sperm motility. Pleiotropic effects were evident, as several SNPs were found to influence multiple motility traits. Candidate genes implicated in essential sperm functions included Myo16 (cytoskeletal dynamics), Cep76 (flagellar structure), and Jarid2 (epigenetic regulation during spermatogenesis), as well as genes involved in membrane integrity, mitochondrial function, and immune regulation. These findings provide novel insights into the genetic architecture underlying sperm motility of Jinding drakes and establish a basis for molecular breeding strategies to enhance reproductive efficiency of waterfowl.

Plumage color is a distinctive and economically important trait in poultry; however, its genetic architecture in hybrid species, such as the mule duck, remains poorly characterized. Traditional mapping approaches often fail to accurately establish causal genes, particularly for traits likely governed by major-effect loci. In this study, we used an integrated multi-omics approach to obtain a deeper understanding of the genetic basis of plumage color in mule ducks. Following whole-genome resequencing of 114 mule duck individuals, a combined analysis involving genome-wide association studies and genome scans for genetic differentiation (F_ST/π) was conducted, which collectively highlighted the EDNRB2 genomic region. Comparative transcriptomics of black versus white feather follicles confirmed that EDNRB2 and key melanogenesis genes were significantly upregulated. This convergence of genomic and transcriptomic evidence was further confirmed by experimental validations. Quantitative polymerase chain reaction confirmed differences in EDNRB2 expression levels, while competitive allele-specific PCR (KASP) genotyping in an independent population revealed a significant association between specific upstream SNPs of EDNRB2 and plumage color scores. Our study revealed EDNRB2 as a pivotal candidate gene regulating plumage color variation in mule ducks. The multi-tiered approach, from population-level genomics to molecular validation, identified a key genetic mechanism, and also provided functionally validated KASP markers, establishing a direct foundation for further developing mule duck breeding in the poultry industry.

To investigate the role of Sertoli cells in duck testicular development and maturation, we conducted single-cell RNA sequencing on testes from immature (IMT) and mature (MT) ducks. Sertoli cells accounted for 27.75 % and 33.42 % of testicular cells in IMT and MT, respectively. We identified 2,630 differentially expressed genes (DEGs) in mature Sertoli cells, with 1,540 upregulated and 1,090 downregulated. Subtype analysis revealed 2,498 DEGs in Sertoli cell type 1 (SC1) (898 up, 1,600 down) and 2,515 DEGs in SC2 (1,291 up, 1,224 down), including 1,090 SC1-specific, 1,107 SC2-specific, and 1,408 shared genes. Gene Ontology analysis showed DEGs were mainly linked to cellular components: SC1 DEGs were enriched in intracellular structures (e.g., nucleus), whereas SC2 DEGs were enriched in membrane- and extracellular-related components (e.g., cell periphery). KEGG pathway analysis highlighted significant enrichment of "Spliceosome," "Neurotrophin signaling," and "MAPK signaling" pathways in MT and IMT, with Neurotrophin signaling predominant in SC1 and MAPK signaling in SC2. Furthermore, the Notch signaling pathway was significantly enriched for SC1-specific genes, whereas the MAPK signaling pathway was significantly enriched for SC2-specific genes. Protein-protein interaction analysis of these pathways identified core genes, including SF3A2, SNRPF, SNRPB2, SNRPG, SF3B4, MAP3K1, NRAS, MET, and EGF. This study delineates developmental dynamics of duck Sertoli cells and offers preliminary insights into regulatory mechanisms underlying testicular maturation, providing a key theoretical and data-driven foundation for understanding Sertoli cell functions in avian testis development.