Yak Gut Microbiota: A Systematic Review and Meta-Analysis

Abstract

The yak (Bos grunniens) is closely related to common cows (Bos taurus), but is clearly a distinct species. Yaks are of substantial importance to food and leather production in certain high-altitude regions of Asia. The animal is increasing elsewhere as well, mainly because of the perceived health benefits of its milk. Like all ruminants, the animal harbors a complex community of microbial cells in its gut, crucial for its physiology. Despite yaks being important domestic animals, the composition of its gut microbiota and how the composition is guided by its specific high-altitude environment remains largely uncategorized. Hence, online databases (Embase, Medline ALL, Web of Science Core Collection, Cochrane Central Register of Controlled Trials, and Google Scholar) were searched for articles on yak intestinal microbiota. The pooled taxonomic abundance was compared between regions, sexes, different age groups, and feeding patterns. The gut microbiota distribution across different yak intestinal segments was established through pooled average taxonomic abundance. A total of 34 studies met the inclusion criteria and yielded information on 982 unique yak gut microbiota samples. An analysis of overall pooled microbiota revealed a segmented microbial community composition of the yak gut. Yak rumen microbiota was significantly influenced by difference in region, sex, and feeding patterns, the latter factor being dominant in this respect. Yak microbiome is shaped by the feeding strategy and provides an obvious avenue for improving health and productivity of the animal. More generally, the current segmental description of physiological gut microbiome provides insight into how the microbiology of this animal has adapted itself to help comping yaks with its high-altitude habitat.

Keywords: environment factors; gut microbiota; rumen microbiota; yak; yak husbandry.

Figure 1

Flowchart diagram of screening and selection processes.

Figure 2

Microbiota distribution in different segments of yak digestive tract. (A) Overview of the segmented yak gastrointestinal system. (B) The composition of microbiota at phylum level in reticulum (n = 9), rumen (n = 481), omasum (n = 9), abomasum (n = 9), duodenum (n = 9), jejunum (n = 9), ileum (n = 9), cecum (n = 9), colon (n = 21), and feces (n = 417). (C) The composition of microbiota at genus level in rumen (n = 129), omasum (n = 9), reticulum (n = 9), and abomasum (n = 9). (D) The composition of microbiota at genus level in yak feces (n = 98). The relative abundance of each taxa was expressed as mean.

Figure 3

A map showing distinctive sampling locations in different areas. There are five provinces identified with different altitudes: Gansu province, Qinghai province, Sichuan province, Tibet, and Yunnan province.

Figure 4

Regional influence on yak rumen microbiota. The relative abundance of phylum (A) and genus levels (B) in rumen microbiota in different provinces was compared, irrespective of the method of yak husbandry. Comparison of the relative abundance of the Firmicutes (C), Bacteroidetes (D), and Proteobacteria (E) in different provinces under the method of grazing vs. feeding. The data were expressed as mean ± SEM. The Mann–Whitney test was applied for intragroup comparison, whereas the Kruskal–Wallis test with post hoc Dunn's test was used for intergroup comparison. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. GS, Gansu province; QH, Qinghai province; SC, Sichuan province; YN, Yunnan province.

Figure 5

Influence of age on yak rumen and fecal microbiota. (A) The relative abundance at the phylum level of rumen microbiota was compared between age groups, irrespective of the method of yak husbandry. The difference of each phylum across different age groups when yak kept grazing (B) and indoor (C). The data were expressed as mean ± SEM. The Kruskal–Wallis test with post hoc Dunn's test was used for multiple comparisons. *p < 0.05, **p < 0.01, ***p < 0.001. (D) Influence of age on yak fecal microbiota. The relative abundance at the phylum level was compared between age groups, irrespective of the method of yak husbandry. The data were expressed as mean ± SEM. The Mann–Whitney test was applied for availability of data. **p < 0.01.

Figure 6

Influence of sex on yak rumen microbiota. (A) The relative abundance of phylum level was compared between male, female, and neutered yaks, irrespective of the method of yak husbandry. (B) The difference in each phylum when yak kept grazing. (C) The difference in each phylum when yak kept indoors. The data were expressed as mean ± SEM. The Mann–Whitney test was applied for intragroup comparison, whereas the Kruskal–Wallis test with post hoc Dunn's test was used for intergroup comparison. *p < 0.05, **p < 0.01.