Fecal Microbial Community Characteristics of Oula and Hu Sheep and Their Correlation with Semen Quality

Semen quality and fecal microbial composition were compared between native Oula rams reared on the Qinghai-Tibet Plateau and Hu sheep rams introduced from lowland regions. Semen quality was analyzed in eight adult Oula rams and eight Hu rams, and fecal microbial composition was assessed via 16S rRNA sequencing. Results indicated that sperm acrosome integrity was significantly higher in Hu sheep than in Oula sheep (p < 0.001); other semen parameters showed no significant differences. Significant differences were also observed in fecal microbial communities between the two breeds. Compared with Hu sheep, Oula sheep exhibited higher microbial abundance and diversity at the phylum level, particularly Campylobacterota, Euryarchaeota, Planctomycetota, Verrucomicrobiota, Myxococcota, and Deferibacterota (p < 0.05). At the genus level, Oula sheep had significantly higher abundances of Treponema, Campylobacter, Methanobrevibacter, UCG-009, Family_XIII_AD3011_group, [Eubacterium]nodatum group, Candidatus Soleaferrea, Akkermansia, and unidentified_Ruminococcaceae (p < 0.05). Correlation analysis indicated associations between sheep semen quality and the top 30 abundant fecal microbial genera. Six genera showed significant positive correlations with acrosome integrity rate, and eight genera exhibited significant negative correlations (p < 0.05). Two genera were correlated positively with plasma membrane integrity rate (p < 0.05). Prevotellaceae_UCG-004 was positively correlated with sperm motility and Progressive Motility spermatozoa proportion (p < 0.05); Ruminococcus showed a significant positive correlation with sperm linear motility and a significant negative correlation with acrosome integrity rate (p < 0.05). These findings indicate that the microbial groups enriched in Oula sheep fecal samples and exhibiting negative correlations with acrosome integrity-including Ruminococcus, Treponema, Akkermansia, and Euryarchaeota-are associated with sperm quality through physiological adaptation mechanisms specific to high-altitude environments.