Abstract: [Objective] Investigate the compositional differences in the semen and intestinal microbiota of Duroc boars during winter and summer, and examine the correlation between predominant microbial communities and semen quality parameters. [Methods] A total of twelve Duroc boars were selected for the collection of fresh sperm and feces samples during both winter and summer. The study utilized 16S rDNA high-throughput sequencing technology to analyze the variations in microbial community composition between semen and fecal samples collected during winter and summer. The computer-aided sperm analysis system was utilized to examine variations in sperm quality parameters across the different seasons. Examine the correlation between the predominant bacterial genera in semen and feces during winter and summer, and their respective associations with semen quality parameters in the corresponding seasons.[Results] There were no statistically significant differences （P>0.05） in the richness and diversity of the bacterial community in the semen of Duroc boars between winter and summer. The Shannon index of fecal flora in summer was significantly higher （P<0.01） compared to winter, while the Simpson index of fecal flora in summer was notably lower （P<0.05） than in winter. Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria are the predominant phyla in semen samples collected during both winter and summer. In summer, the dominant genera include Achromobacter, Terribacillus, Porphyromonas, among others, whereas in winter, Pseudomonas, Brochothrix, Achromobacter, and others dominate. Notably, the relative abundances of Pseudomonas and Carnobacterium in winter semen samples were significantly higher （P<0.01） compared to those in summer. The Firmicutes, Bacteroidetes, Spirochaetes, and Proteobacteria were the predominant phyla in fecal samples during both winter and summer. The relative abundance of Firmicutes was significantly higher in winter （P<0.01） compared to summer, whereas the relative abundances of Bacteroidetes and Spirochaetes were significantly lower （P<0.05）, and that of Proteobacteria was markedly reduced （P<0.01）. Dominant genera in summer feces included Terrisporobacter, Turicibacter, Treponema, among others, while Streptococcus, Terrisporobacter, and Clostridium leptum group 1 were more prevalent in winter. Specifically, the relative abundance of Streptococcus was significantly higher in winter （P<0.05）, Clostridium leptum group 1 showed a marked increase （P<0.01）, Ruminococcaceae UCG-005 was significantly lower （P<0.01）, and Escherichia-Shigella, Christensenellaceae R-7, and Prevotellaceae NK3B31 exhibited significant reductions （P<0.05） in winter compared to summer. The relative abundance of Acinetobacter in summer semen exhibited a significant negative correlation （P<0.05） with sperm motility during the same season. Additionally, the relative abundance of Achromobacter showed an extremely significant negative correlation （P<0.01） with sperm density in summer. In winter, the relative abundance of Pseudomonas was significantly positively correlated （P<0.05） with semen volume. Furthermore, the relative abundance of Clostridium leptum 1 in summer feces demonstrated a significant positive correlation （P<0.05） with sperm motility in summer, while the relative abundance of Turicibacter was significantly negatively correlated （P<0.05） with sperm density in summer. The sperm deformity rate in Duroc boars during winter was significantly lower （P<0.01） compared to that in summer. [Conclusion] Seasonal variations influenced the composition of bacterial microbes in the semen and intestine of Duroc boars, revealing correlation between certain dominant bacterial genera in both the semen and intestines and semen quality. The findings of this study provide a foundational basis for enhancing and preserving semen quality in boars during winter and summer.

Key words: Duroc boar, microbial diversity, semen quality, seasons