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There are many kinds of microorganisms in the gastrointestinal tract of mammals, some of which are closely related to the host. Rumen microorganisms are essential for normal physiological activities of their host by decomposing plant crude lignin and providing essential nutrients. The composition and diversity of this microbial population are influenced by the host, environment, and diet. Despite its importance, little is known about the effects of factors such as altitude variation on rumen microbial population abundance and diversity in different ruminants. Here, we described the changes in overall rumen bacteria in four groups of cattle, including the Zhongdian yellow cattle and Zhongdian yaks, grazing at high altitudes (3600 m); the Jiangcheng yellow cattle and Jiangcheng buffalo were kept at an altitude of 1100 m. We found that there was a significant difference in rumen bacterial abundance of the Zhongdian yellow cattle and Zhongdian yaks at high altitude and there was obvious homogeneity in rumen bacterial abundance and diversity in the Jiangcheng yellow cattle and Jiangcheng buffalo at low altitude. Therefore, our research concluded that under the same dietary environment, there were differences in the abundance and diversity of certain bacteria in the rumen of different breeds of cattle, indicating that host genetic factors and intestinal microorganisms related to altitudinal variation had a greater influence on rumen bacterial abundance in the cattle.

The rumen of ruminants is inhabited by complex and diverse microorganisms. Young animals are exposed to a variety of microorganisms from their mother and the environment, and a few colonize and survive in their digestive tracts, forming specific microflora as the young animals grow and develop. In this study, we conducted full-length sequencing of bacterial and fungal communities in the rumen of pastured yaks of different ages (from 5  days after birth to adulthood) using amplified sequencing technology. The results showed that the rumen microflora of Zhongdian yaks changed gradually from 5 to 180  days after birth and tended to stabilize at 2  years of age. The rumen of adult yaks was the most suitable for the growth and reproduction of most bacteria. Bactria diversity of the yak rumen increased gradually from 5  days after birth to adulthood. With the growth of yaks, different dominated bacteria were enriched in different groups, but Prevotella remained highly abundant in all groups. The yak rumen at 90  days of age was the most suitable for the growth and reproduction of most fungi, and 90 days of age could be a cut-off point for the distribution of fungal communities. Fungal Thelebolus was the firstly reported in yak rumen and was enriched in the yak rumen of 90  days after birth. The most abundant and balanced fungal genera were found in adult yaks, and most of them were only detected in adult yaks. Our study reported on the rumen bacterial and fungal communities of Zhongdian yaks grazed at different ages and provided insights into the dynamic changes of dominant microflora with yak growth.

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