Abstract
The yak is one of the most important domestic animals in Tibetan life for providing basic resources such as milk, meat and transportation. Although yak milk production is not elevated, yak milk is superior to dairy cow milk in nutrient composition (protein and fat). However, the understanding of the metabolic mechanisms of yak mammary gland tissue during the lactation cycle remains elusive. In this study, GC-MS-based metabolomics was employed to study the metabolic variations in the yak mammary gland during the lactation cycle (pregnancy, lactation and dry period). Twenty-nine metabolites were up or downregulated during the lactation period. Compared to the dry period, during the lactation period the levels of oxalic acid were upregulated, while glycine and uridine were downregulated. Thirty-seven pathways were obtained when the 29 differential metabolites were imported into the KEGG pathway analysis. The most impacted pathways during the lactation cycle were glycine, serine and threonine metabolism; alanine, aspartate and glutamate metabolism; TCA cycle; glyoxylate and dicarboxylate metabolism; and pyrimidine metabolism. Our results provide important insights into the metabolic events involved in yak mammary gland development, lactogenesis and lactation, which can guide further research to improve milk yield and enhance the constituents of yak milk.
Highlights
The yak (Bos grunniens) lives in regions centered on the Chinese Qinghai-Tibet Plateau, including the highlands of Nepalese Himalayas, Indian Kasmir, Tibet, Mongolia and Bhutan [1] at high altitudes from 2000–5000 m where few other animals can survive
As shown in S1 Fig. no drift was observed in the principal component analysis (PCA) scores plot representation of quality control (QC) samples
37 pathways were obtained when the 29 differential metabolites were imported into the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis
Summary
The yak (Bos grunniens) lives in regions centered on the Chinese Qinghai-Tibet Plateau, including the highlands of Nepalese Himalayas, Indian Kasmir, Tibet, Mongolia and Bhutan [1] at high altitudes from 2000–5000 m where few other animals can survive. Yak milk and milk products are the major dietary ingredients for 6.5 million Tibetan people as well as it is an important source of income to the local families. For these reasons, the yak is one of the most important domestic animals in Tibetan life [3], and the yak daily industry has rapidly grown in recent years [4].
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