Here we aimed to explore the change in yak gut microbiota after transferring yaks from grazing grassland to a feedlot, and determine their diet adaptation period. Five yaks were transferred from winter pasture to an indoor feedlot. Fecal samples were obtained from grazing (G) and feedlot feeding yaks at day 1 (D1), day 4 (D4), day 7 (D7), day 11 (D11), and day 16 (D16). The dynamic variation of the bacterial community was analyzed using 16S rRNA gene sequencing. The results showed that the yak gut microbial community structure underwent significant changes after diet transition. At the phylum and genus levels, most bacteria changed within D1–D11; however, no significant changes were observed from D11–D16. Furthermore, we used random forest to determine the key bacteria (at class level) disturbing gut micro-ecology. The relative abundance of the top four classes (Erysipelotrichia, Gammaproteobacteria, Saccharimonadia, and Coriobacteriia) was highest on D1–D4, and then decreased and plateaued over time. Our results demonstrated that an abrupt adjustment to a diet with high nutrition could influence the gut micro-ecology, which was stabilized within 16 days, thus providing insights into diet adaptation in the yak gut.

This study aimed to comprehensively evaluate the characteristics in the longissimus thoracis et lumborum (LTL) muscle of Chaka (CK) sheep and Tibetan (TB) sheep, and transcriptomics–metabolomics association analysis was used to find the possible genes, differential metabolites, and significant differential metabolic pathways that lead to meat quality differences. Based on the researched results, the nutritional quality of meat, including the contents of ether extract (11.95% vs. 10.56%), unsaturated fatty acid (51.20% vs. 47.69%), and polyunsaturated fatty acid (5.71% vs. 3.97%), were better in TB sheep than in CK sheep, while the CK sheep has better muscle fiber characteristics, such as the total number (62 vs. 45) and muscle fiber density (1426.54 mm² vs. 1158.77 mm²) and flavor. Omics research has shown that the key differential metabolites and metabolic pathways were dominated by amino acid metabolism, particularly the glutathione metabolism, taurine and hypotaurine metabolism, and lipid metabolism-related pathways, such as glycerophospholipid metabolism and the sphingolipid signaling pathway. The intermediate metabolite sn-Glycerol 3-phosphoethanolamine played a key role in determining sheep meat quality, which was regulated by GPAT2, PLPP2, AGPAT1, PNPLA2, and GPAT4 and correlated with meat color, texture, and flavor. Overall, these results will provide effective information and more evidence to support further exploration of valuable biomarkers of meat quality.

The objective of this study was to investigate and compare fatty acids and metabolites in the longissimus dorsi muscle between Black Tibetan and Chaka sheep grazing in a highly saline environment. A total of eight castrated sheep (14 months old) with similar body weights (25 ± 2.2 kg) were selected. The experimental treatments included Black Tibetan (BT) and Chaka sheep (CK) groups, and each group had four replications. The experiment lasted for 20 months. All sheep grazed in a highly saline environment for the whole experimental period and had free access to water. The results showed that the diameter (42.23 vs. 51.46 $\mathsf{\mu }$m), perimeter (131.78 vs. 166.14 $\mathsf{\mu }$m), and area of muscle fibers (1328.74 vs. 1998.64 $\mathsf{\mu }$m²) were smaller in Chaka sheep than in Black Tibetan sheep. The ash content in the longissimus dorsi was lower in Chaka sheep than in Black Tibetan sheep (p = 0.010), and the contents of dry matter (DM), ether extract (EE), and crude protein (CP) in the longissimus dorsi showed no differences (p > 0.05). For fatty acids, the proportions of C10:0, C15:0, and tC18:1 in the longissimus dorsi were higher in Chaka sheep than in Black Tibetan sheep (p < 0.05). However, all other individual fatty acids were similar among treatments, including saturated fatty acids (SFAs), unsaturated fatty acids (UFAs), monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), and the ratios of n-6 PUFAs to n-3 PUFAs and PUFAs to SFAs (p > 0.05). A total of 65 biomarkers were identified between the two breeds of sheep. Among these metabolites, 40 metabolic biomarkers were upregulated in the CK group compared to the BT group, and 25 metabolites were downregulated. The main metabolites include 30 organic acids, 9 amino acids, 5 peptides, 4 amides, 3 adenosines, 2 amines, and other compounds. Based on KEGG analysis, eight pathways, namely, fatty acid biosynthesis, purine metabolism, the biosynthesis of unsaturated fatty acids, renin secretion, the regulation of lipolysis in adipocytes, neuroactive ligand–receptor interaction, the cGMP-PKG signaling pathway, and the cAMP signaling pathway, were identified as significantly different pathways. According to the results on fatty acids and metabolites, upregulated organic acid and fatty acid biosynthesis increased the meat quality of Chaka sheep.

In the current research, samples of yak gastrointestinal tracts (GITs) were used to profile the bacterial compositional characteristics using high through-put sequencing technology of 16S RNA amplicon. A total of 6959 OTUs was obtained from 20,799,614 effective tags, among which 751 OTUs were shared by ten sections. A total of 16 known phyla were obtained in all samples—the most abundant phyla were Firmicutes (34.58%), Bacteroidetes (33.96%) and Verrucomicrobia (11.70%). At the genus level, a total of 66 genera were obtained—Rikenellaceae_RC9_gut_group (7.24%), Akkermansia (6.32%) and Ruminococcaceae_UCG-005 (6.14%) were the most abundant. Species of Observed (Sob), Shannon and Chao values of the Stomach were the greatest, followed by the large intestine, while small intestine had the lowest diversity (p < 0.05). Bacteroidete were more abundant in sections from rumen to duodenum; while Firmicutes were the most abundant in sections from jejunum. ABC transporters (7.82%), Aminoacyl-tRNA biosynthesis (4.85%) and Purine metabolism (3.77%) were the most abundant level-3 pathways in all samples. The results of associated correlation analysis indicated that rectum samples might be used as an estimator of rumen bacterial communities and fermentation. The results of this research enrich the current knowledge about the unique animals of the QTP and extend our insight into GITs microecology of various animals.

Shifts in feeding regimes are important factors affecting greenhouse gas (GHG) emissions from livestock farming. However, the quantitative values and associated drivers of GHG emissions from yaks (Bos grunniens) following shifts in feeding regimes have yet to be fully described. In this study, we aimed to investigate CH₄ and CO₂ emissions differences of yaks under different feeding regimes and their potential microbial mechanisms. Using static breathing chamber and Picarro G2508 gas concentration analyzer, we measured the CO₂ and CH₄ emissions from yaks under traditional grazing (TG) and warm-grazing and cold-indoor feeding (WGCF) regimes. Microbial inventories from the ruminal fluid of the yaks were determined via Illumina 16S rRNA and ITS sequencing. Results showed that implementing the TG regime in yaks decreased their CO₂ and CH₄ emissions compared to the WGCF regime. The alpha diversity of ruminal archaeal community was higher in the TG regime than in the WGCF regime. The beta diversity showed that significant differences in the rumen microbial composition of the TG regime and the WGCF regime. Changes in the rumen microbiota of the yaks were driven by differences in dietary nutritional parameters. The relative abundances of the phyla Neocallimastigomycota and Euryarchaeota and the functional genera Prevotella, Ruminococcus, Orpinomyces, and Methanobrevibacter were significantly higher in the WGCF regime than in the TG regime. CO₂ and CH₄ emissions from yaks differed mainly because of the enrichment relationship of functional H₂- and CO₂-producing microorganisms, hydrogen-consuming microbiota, and hydrogenotrophic methanogenic microbiota. Our results provided a view that it is ecologically important to develop GHG emissions reduction strategies for yaks on the Qinghai–Tibet Plateau based on traditional grazing regime.

The gut microbiota in different diets helps hosts to obtain sufficient nutrients from food, which is important for wild yaks in the Qinghai-Xizang Plateau to adapt to different seasons. The relationship between the host diet and the gut microbiota in different seasons is important for exploring the adaptation of these wild yaks to their environments. This study used wild yaks as a model organism. Using high-throughput sequencing and liquid chromatography-mass spectrometry, we investigated their seasonal diet, gut microbiota composition and function, and short-chain fatty acid profiles. The inter-season differences in them were compared, and relationships among these differences were explored. Wild yaks in summer had a diet higher in Polygonaceae and lower in Rosaceae compared to their diets in autumn and winter. The broadest dietary niche width (8.8449) was detected in autumn, and the lowest diet niche overlap (0.3751) was found between summer and winter. Co-occurrence network analyses revealed that microbial interactions were more complex in autumn, likely due to transitional dietary adjustments, whereas summer and winter exhibited simpler but more robust interactions. The abundance of Firmicute increased in winter, suggesting enhanced energy extraction from low-quality forage. Specific taxa, such as Alistipes_A in autumn and Romboutsia in winter, were linked to key metabolic pathways, including carbohydrate degradation and short-chain fatty acid production. The study highlights the critical role of gut microbiota plasticity in facilitating wild yaks' adaptation to the extreme and variable conditions and provides the basis for explaining the harsh environment adaptation of wild herbivores in the Qinghai-Xizang Plateau.