Metagenomic identification of bull semen microbiota in different seasons.

A seasonal effect on sperm quality parameters was observed previously. Although identification of the bull semen microbiota by 16S rRNA sequencing was performed previously, it has not been carried out in commercial semen samples from different seasons, and its connection with sperm quality parameters has not been evaluated yet. The objectives in this study were; (i) to evaluate diversity of bull semen microbiota and sperm quality parameters in different seasons, and (ii) to find if specific bacteria were associated with seasonal differences in specific sperm quality parameters. Bull semen microbiota was identified in 54 commercial bull semen samples from 3 seasons (winter, spring, summer). Sperm quality was analysed by Computer Assisted Sperm Analyses (CASA) and Flow Cytometry (FC). From 28 phyla in all samples, six phyla were identified in samples from all seasons, with observed seasonal differences in their distribution. At genus level, 388 genera were identified, of which 22 genera had a relative abundance over 1 % and showed seasonal differences in bacterial diversity, and 9 bacteria genera were present in all seasons. Differences between spring and summer (P < 0.05) were observed for live hydrogen peroxide positive sperm cells. A trend towards significance (0.10 > P > 0.05) was observed for some CASA kinematics (VCL and LIN) and FC parameters (High respiratory activity, and live hydrogen peroxide positive sperm cells) between seasons. Nevertheless, associations between sperm quality parameters and specific bacteria were observed in spring.