Abstract: To explore the microbial community dynamics, differential metabolites and potential metabolic pathways in the milk of yak and cattle-yak in Gannan area, this study selected 6 yaks and 6 cattle-yak from the same natural grazing condition. Milk samples were collected from these animals for analysis of microbial communities and metabolites by single-molecule real-time sequencing and non-targeted metabolomics. The results showed that there was no significant difference in the microbial diversity or community composition between yak and cattle-yak milk (P > 0.05), while the bacterial abundance in the cattle-yak milk was higher than that in yak milk. The dominant bacterial phyla in the two types of milk were Proteobacteria, Firmicutes and Bacteroidota. The dominant genera in yak milk were Bacteroides, unclassified_Sphingobacteriaceae, unclassified_Muribaculaceae, Lachnospiraceae_NK4A136_group, and Prevotellaceae_UCG_001, while those in cattle-yak milk were Lactobacillus, Bacteroides, and Streptococcus. The metabolites D-glucosamine-6-phosphate, indole-3-methanol, N-methyl-L-aspartic acid, histidine betaine, and histidine-glutamate in yak milk might enhance its nutritional value by improving lipid stability, antioxidant capacity, and the efficiency of protein synthesis; while the metabolites linoleic acid and 3-methoxy-4-hydroxybenzaldehyde in cattle-yak milk might affect its oxidative stability and flavor characteristics. In conclusion, under the same grazing conditions, there was no significant difference in microbial diversity between the milk of yak and cattle-yak. However, the microbial communities of cattle-yak milk exhibited higher richness than those of yak milk. The metabolic characteristics of yak milk were related to nutritional fortification and antioxidant/protein synthesis, while the metabolic characteristics of cattle-yak milk might be related to the regulation of oxidative stability and flavor characteristics.

Key words: yak milk; cattle-yak milk; microbial diversity; non-targeted metabolomics