Response of rumen microbiota from yaks among the three regions. (A) Composition of rumen microbiota from yaks inhabiting regions located at distinct altitudes (OTU-level analysis). (B) PCoA analysis of rumen microbiota from yaks inhabiting regions located at distinct altitudes. HAL, high-altitude region (Zhongba County, Xigatse City; 4,800 m); MAL, medium-altitude region (Nagqu City; 4,500 m); LAL, low-altitude region (Dangxiong County, Lhasa City; 3,800 m).
Next, we proceeded with bacterial identification of the 30 samples at different levels. At the phylum level, the top five ruminal bacteria of yaks across all samples were Bacteroidetes (50.69%), Firmicutes (41.11%), Proteobacteria (1.45%), Tenericutes (1.40%), and Actinobacteria (1.05%) (Figure 2A and Supplementary Table 1). The MAL group presented the lowest (p
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Compositional profiles of rumen microbiota from yaks inhabiting regions located at distinct altitudes. (A) Phylum level, (B) family level, and (C) genus level. HAL, high-altitude region (Zhongba County, Xigatse City; 4,800 m); MAL, medium-altitude region (Nagqu City; 4,500 m); LAL, low-altitude region (Dangxiong County, Lhasa City; 3,800 m).
LEfSe analysis of rumen microbiota from yaks inhabiting regions located at distinct altitudes. (A) Histogram of linear discriminant analysis scores based on Classification Information. (B) Linear discriminant analysis effect size cladogram based on Classification Information. HAL, high-altitude region (Zhongba County, Xigatse City; 4,800 m); MAL, medium-altitude region (Nagqu City; 4,500 m); LAL, low-altitude region (Dangxiong County, Lhasa City; 3,800 m).
Ruminants rely on VFAs produced in the rumen during fermentation as a source of energy. Indeed, their feed efficiency is related to such VFAs (Lam et al., 2018; Zhou et al., 2018). While propionic acid can supply additional energy to ruminants, acetic and butyric acids are converted to methane and carbon dioxide during the consumption process, lowering energy efficiency (Gunun et al., 2018). Propionic acid and butyric acid compete with methane for hydrogen during fermentation, reducing methane energy consumption while improving energy supply (Pragna et al., 2018). Acetic acid and butyric acid originate mainly from the fermentation of fiber, whereas propionic acid derives from the fermentation of sugar and starch (Astawa et al., 2011). In this study, VFAs and propionic acid were highest in the rumen of MAL animals, suggesting that feed efficiency might be better in this than in the other groups. Contrary to the present results, Zhang et al. (2016) found that ruminants living at elevated altitude had higher VFA content and significantly upregulated genes responsible for VFA absorption in the rumen. Diet is the most important factor regulating development and colonization of rumen microbiota (Zhou et al., 2018; Lin et al., 2019; Myer, 2019). Ram (2005) reported that meadows found at different elevation in the Uttaranchal Himalaya exhibited distinct species richness. Similarly, Bao et al. (2021) linked the alpine meadows between Dangxiong and Nagqu regions of Tibet with a varied nutritional value. Regional variation could be related to temperature differences between day and night, photosynthesis, and topography (Han et al., 1997; Skapetas et al., 2004). Accordingly, further experiments are required to ascertain whether the observed differences are due to the extreme climatic conditions and altitude tested in this study or to the quality of grass in the different regions. Furthermore, the alpha and beta diversity indices of rumen microbiota differed significantly between the three groups, indicating a close relationship between the diversity of rumen microbiota in yaks and geographic location. Interestingly, unlike VFAs, the diversity of ruminal microbiota first decreased and then increased with elevation. Shabat et al. (2016) found that microbiota diversity correlated negatively with feed efficiency, with efficient dairy cattle exhibiting lower rumen microbiota diversity, methane emission, and acetic acid concentration, but higher propionic acid content. Taking into account those and the present results, it appears that yaks in the MAL group are more efficient at utilizing their pasture and emit less methane.
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