Study on comparative analysis of differential metabolites in Guanzhong dairy goat semen before and after freezing

In order to explore the differential metabolites between fresh and frozen-thawed semen of Guanzhong dairy goats, semen samples were collected by artificial vagina method, and divided into fresh and frozen-thawed semen groups, with six replicates in each group. Liquid Chromatography-mass spectrometry (LC-MS) technology was used to detect semen metabolites in both groups. The metabolites were analyzed and identified by the combination of multidimensional statistical analysis, namely principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), orthogonal partial least squares discriminant analysis (OPLS-DA) and univariate statistical analysis, Differential metabolites were identified according to One-step Solution for Identification of Small Molecules in Metabolomics Studies (OSI/SMMS) combined with Human Metabolome Database (HMDB), Lipidmaps and Metlin and the metabolic pathways of different metabolites were enriched and analyzed by Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The results showed that a total of 53 differential metabolites were detected in fresh and frozen-thawed semen groups, of which 10 metabolites were significantly up-regulated (P < 0.05) and 43 were significantly down-regulated (P < 0.05). Most of the metabolites belonged to lipids and lipid-like molecules, organic acids and their derivatives, organic oxygen compounds, etc. According to the functional enrichment analysis of the top twenty differential metabolites in the KEGG database, significant changes occurred in linoleic acid metabolism pathway out of total eleven pathways observed. These differential metabolites can be used as metabolic markers of sperm cryo-injury in dairy goats.