Puberty status influences bacterial communities of the boar urogenital tract

Bacteria present in fresh extended boar semen may impair the fertility of artificial insemination doses in swine. To date, information regarding the presence or composition of bacterial communities within the boar's urogenital tract is lacking. These unexplored communities may contribute to the bacterial composition of semen and thereby influence boar fertility. Moreover, hormonal and anatomical changes that occur during puberty could also alter the urogenital tract bacterial communities. Therefore, the objective of this study was to evaluate pre- and post-pubertal shifts in bacterial communities and diversity in boar urogenital tissues (i.e., testis, epididymis, seminal vesicle, prostate, bulbourethral gland, bladder, and preputial diverticulum) using 16S rRNA gene amplicon community sequencing. Crossbred boars were euthanized at 74 ± 2 days of age (pre-pubertal; n = 4) or 276 ± 3 days of age (post-pubertal; n = 6), and intact reproductive tracts were harvested. Sterile swab samples were collected from each tissue of interest for microbiota analysis, and plasma was collected to analyze circulating hormone concentrations of testosterone and dihydrotestosterone. Circulating testosterone was greater (P < 0.01) in post-pubertal boars compared to pre-pubertal boars (3.01 ± 0.26 vs. 0.96 ± 0.36 ng/mL) yet no differences were observed in dihydrotestosterone concentrations. The relative abundance of the phylum Firmicutes was elevated (P < 0.05) in the testis, epididymis, seminal vesicle, bulbourethral gland, and preputial diverticulum of pre-pubertal boars and negatively correlated (P < 0.05) with testosterone. Alternatively, the relative abundance of the phylum Proteobacteria was greater in those same tissues from post-pubertal boars (P < 0.05) and was positively correlated (P < 0.05) with testosterone. Alpha-diversity was reduced in the urogenital tracts of post-pubertal boars compared to pre-pubertal boars (P < 0.01). The bladder had greater alpha-diversity compared to other tissues (P < 0.05). Pre- and post-pubertal boar urogenital tissues have distinct bacterial communities and shifts in these communities following puberty attainment may be associated with elevated testosterone. Future research is warranted to compare bacterial compositions of the boar urogenital tissues to the animal's ejaculate, which would provide greater insight into the origin of bacteria within boar semen.