Impact of sex and age on the bacterial composition in rumen of Tibetan sheep in Qinghai China.

• Rumen bacteria community of Tibetan sheep was predominated by phyla Bacteroidetes, Firmicute and Verrucomicrobia at phylum level, as to genus , Rikenellaceae_RC9_gut_group and Prevotella_1 predominated. • Sex and age were two important factors which shaping the rumen bacterial composition of Tibetan sheep as previous reported on mice and human. • Most of predicted function genes significantly enriched in adult female sheep compared with adult male sheep and yearling female sheep, respectively. In this study, 18 Tibetan sheep were assigned into four groups by age and sex, namely young ewes (E1, n = 5), young rams (R1, n = 3), adult ewes (EA, n = 5) and adult rams (RA, n =5) to profile the bacterial composition of Tibetan sheep and to explore the impacts of sex and age on rumen microbiota using high-throughput sequencing method of amplicon of 16S rRNA V3–V4 region. The results indicated that all effective tags for 18 samples were clustered into 5429 OTUs (Operation taxonomic Units, OTUs) with an absolute abundance > 1 at a similarity level > 97%. The rumen bacterial composition of female adult sheep was more diverse than male adult sheep and yearling female sheep. SILVA database was used to annotate taxonomic information for each representative sequence using the RDP classifier, the results showed that Bacteroidetes, Firmicutes, Verrucomicrobia and Proteobacteria were the most dominant phyla, representing 56.68%, 28.81%, 6.71% and 1.73% of reads from all samples on average, respectively. At the genus level, Rikenellaceae_RC9_gut_group , and Prevotella_1 were most abundant with relative abundance of 12.98% and 11.19%, respectively. Relative abundance of Bacteroidetes in EA was greater than RA (p = 0.014), relative abundance of Firmicutes in RA was greater than EA (p < 0.001), and the relative abundance of Spirochaetae in E1 was greater than R1 (p = 0.038). Shifting genera between the sexes belonged to Order Bacteroidales and Clostridiales , both changed substantially across sex in adult sheep (p < 0.01). The abundance of Bacteroidetes in female sheep and Firmicutes and Planctomycetes in male sheep significantly increased with age (p < 0.05), while the abundance of Spirochaetae in female sheep and Cyanobacteria in male sheep decreased with age (p < 0.05). Shifting genera between age groups belonged to order Bacteroidales and Clostridial. The abundance of order Bacteroidales in female sheep increased with age (p = 0.046), and the abundance of order Clostridiales in male sheep increased with age (p = 0.006), while it decreased with age in female sheep (p = 0.030). In summary, this study profiled the bacterial composition characteristics of Tibetan sheep and concluded that physiological factors, e.g. sex and age, shaped the bacterial composition, which expands our knowledge of the rumen of ruminant animals residing on the Qinghai-Tibetan Plateau. [ABSTRACT FROM AUTHOR]