Abstract: The differences in metabolites and related metabolism pathways in colostrum and mature milk from Saanen goats at different lactation stages were explored by untargeted metabolomics based on ultra-high performance liquid chromatography-quadrupole electrostatic field orbitrap mass spectrometry (UPLC-QE-orbitrap-MS). The results showed that a total of 118 differential metabolites were found between colostrum and mature milk, among which 62 had higher relative contents in colostrum than in mature milk and 56 had lower relative contents in colostrum than in mature milk. These metabolites were mainly lipids, amino acids, and nucleosides. Nine key metabolic pathways most associated with these metabolites were selected, which jointly regulated the lactation process of Saanen goats, and the citric acid cycle could act as a bridge connecting other metabolic pathways. The number of differential metabolites involved in these metabolic pathways was 12. The differential metabolites with relatively high contents in colostrum were taurine, hypotaurine, taurocholic acid, L-phenylalanine, L-tyrosine, succinic acid, isocitrate, D-maltose, α-lactose, 4-hydroxyphenylpyruvate and glycine. The differential metabolite with relatively high contents in mature milk was N1-methyl-4-pyridone-3-carboxamide. They could be used as potential marker metabolites in the colostrum and mature milk of Saanen goats. Metabolomics technology can also be used for identifying differential metabolites in milk from other dairy species at different lactation stages.

Key words: metabolomics; Saanen goat; colostrum; mature milk; differential metabolites