Characterizing the seminal microbiota in mature rams managed on divergent planes of nutrition, and their male offspring

Evidence suggests that there is a rich and diverse microbial community in the semen of mammals, which may be important in reproductive health and fertility. However, the composition of ram seminal microbiota remains under-characterized, with factors shaping it still largely unknown. The objectives of this study were to; 1) characterize the seminal microbiota of mature rams and their ram lambs using 16S rRNA gene sequencing; 2) evaluate whether managing the mature rams on divergent planes of nutrition can influence their seminal microbiota and that of their male offspring; and 3) compare the seminal microbiota between mature rams and ram lamb cohorts to identify age-related microbiota characteristics. For this, mature rams (n = 24) were assigned to one of the 3 nutritional planes: 1) Positive (POS), to gain 12% of initial body weight (BW) (n = 8), 2) maintenance (MAINT), to maintain BW (n = 8), and 3) negative (NEG), to lose 12% BW (n = 8) over an 84-d period. Semen samples were collected from the mature rams (F0) after 28-d, 56-d, and 84-d from the start of the trial. Following the 84-d period, the 24 rams were used to breed 240 mature ewes over 28-d. After lambing, the ram lambs (F1) sired by POS, MAINT, and NEG rams were maintained on the same diet until 11 months of age, at which semen samples were collected. Genomic DNA was extracted from the semen, and the microbiota was analyzed using 16S rRNA gene (V3-V4) sequencing. Overall, there was a relatively diverse and dynamic bacterial microbial community in the ram semen, mainly dominated by Actinobacteriota, Bacillota, Bacteroidota, and Proteobacteria phyla. The predominant genera identified included Fastidiosipila, Corynebacterium, Trueperella, Arthrobacter, Dietzia, and Bifidobacterium. The seminal microbial community structure, composition, and alpha diversity of F0 rams was influenced by diet during the first 28-d, but these diet influences later diminished. The paternal plane of nutrition did not influence the seminal microbiota of offspring ram lambs. The mature rams and ram lambs had distinct seminal microbiota, with young rams showing greater microbial richness and diversity (P < 0.005). Our results suggest that there is a relatively diverse and dynamic microbial community present in the semen of both mature rams and ram lambs, and that this microbiota is transiently influenced by diet and age. Managing rams on divergent planes of nutrition may not affect their offspring's seminal microbiota.