Associations Between Milk Composition, Blood Metabolomics, and Systemic Physiological Indices in High- vs. Low-Yielding Guanzhong Dairy Goats During Early Lactation

This study aimed to elucidate the intrinsic regulatory mechanisms by comparing milk quality, blood metabolomics, and physiological indices between high-yielding (BH, <i>n</i> = 15, high milk yield, daily milk yield with 4.08 ± 0.17 kg) and low-yielding (BL, <i>n</i> = 15, low milk yield, daily milk yield with 2.54 ± 0.26 kg) Guanzhong dairy goats during early lactation. The results showed that the lactose content in the BH group was significantly lower than that in the BL group (<i>p</i> < 0.05), but the total daily lactose yield was 60 g higher. No significant differences were observed in milk fat or milk protein (<i>p</i> > 0.05). Among blood biochemical indices, total protein (TP), glucose (GLU), and alkaline phosphatase (ALP) were significantly lower in the BH group (<i>p</i> < 0.05), while β-hydroxybutyrate (BHBA) was significantly higher (<i>p</i> < 0.05). Milk yield exhibited a highly significant negative correlation with TP and creatinine (CRE). Regarding immune and antioxidant indices, catalase (CAT), glutathione peroxidase (GSH-Px), IgM, and IL-2 were significantly elevated in the BH group (<i>p</i> < 0.05), while IL-6 was significantly reduced (<i>p</i> < 0.05). CAT and IL-2 showed positive correlations with milk yield. Using a subset of animals for in-depth profiling (<i>n</i> = 6 per group)Serum metabolomics identified 184 differential metabolites (114 upregulated, 70 downregulated). In the BH group, betaine, acylcarnitines, and L-valine exhibited significant negative correlations with milk yield, implicating pathways related to fatty acid -oxidation, methyl donor regulation, and amino acid metabolism. These findings indicate that high-yielding dairy goats achieve efficient lactation through enhanced fatty acid β-oxidation, optimized methyl donor regulation for milk fat synthesis, and prioritized allocation of amino acids towards the mammary gland.