Exploring Yak (Bos grunniens) Rumen Bacterial and Fungal Communities from 5 Days after Birth to Adulthood

The gut microbial community of mammals, especially ruminants, plays an important role at different ages of the host. Ruminants have a unique compartment in their digestive tract; the rumen, comprising microorganisms that can effectively decompose plant fibers for the host to transform into milk and for growth and development, which is important for meat production. Colonization of rumen microorganisms is closely related to host developmental stage and affects host performance production. There is little information regarding initial colonization and subsequent changes of the rumen microbial population in wild grazing animals, from birth to adulthood. This study investigated the rumen bacterial and fungal populations of grazing yaks in five experimental groups, ranging from a few days after birth to adulthood using amplicon sequencing. Results indicated that rumen microbial communities of these yaks undergo a gradual change from 5 to 180 days after birth, with the bacterial and fungal diversity stabilizing at the age of 2 years. Additionally, Ruminococcus was detected in 5-day-old yak rumens, with a high percentage of Penicillium and other microbial species are important for normal rumen function detected in the adult rumen. The changes to the yak rumen microbial community after birth were reflected in the increased anaerobic fiber degradation group, and decreased aerobic and facultative anaerobic bacteria. Microbial diversity and abundance in the yak rumen increased with age. Rumen microbial composition of 6-month and 2-year-old yaks had obvious homogeneity. There were some differences in dominant rumen microorganisms among the different age groups. Further studies are required to confirm the functions of these differential and dominant microorganisms in each age group.