Effect of Astragalus membranaceus Root on the Serum Metabolome of Preweaning Dairy Calves

The effect of the Astragalus membranaceus root (AMR) on the serum metabolic profiles of preweaning calf were investigated in this study. Sixteen preweaning Holstein calves were randomly allocated into two groups with eight calves per group, and offered a control basal diet (CON group) or supplemented with 20 g superfine powder of AMR (AMR group) for 14 day. Serum samples were collected from calves on day 0, 7 and 14. Serum albumin, globulin, total protein, glucose, reduced glutathione and superoxide dismutase were evaluated. Serum metabolic profiling was analyzed using ultra-high-performance liquid chromatography–time-of-flight mass spectrometry. The results demonstrated that there were no significantly difference of total protein, glucose, reduced glutathione and superoxide dismutase between the CON group and AMR group (p > 0.05), while within the CON group and AMR group, serum glucose showed a continuous upward trend from 0 day to 14 day (p < 0.001). Untargeted metabolomics analysis found the metabolism of preweaning calf was considerably changed during growth, mainly including amino acid metabolism and carbohydrate metabolism and showed an increasing in protein synthesis and gluconeogenesis. 19 differential metabolites have been screened after supplementing AMR for 14 day, nine of which were up-regulated, including ornithine, L-pyroglutamic acid, L-proline and D-proline, and 10 down-regulated, containing L-kynurenine, 5-hydroxyindoleacetate, linoleic acid and 4-pyridoxic acid. Pathway analysis found these metabolites mainly participated in three primary pathways: arginine and proline metabolism, tryptophan metabolism and glutathione metabolism (p < 0.05), while linoleic acid metabolism and vitamin B6 metabolism were also enriched (0.1 < p < 0.05). Such metabolic changes reflected the enhancement of the antioxidant and anti-inflammatory capacity of preweaning calves.