Comprehensive Metabolomic Profiling of Goat Milk across Lactation Stages: Identification of Milk Composition and Stage-Specific Biomarkers

Goat milk is highly nutritious and represents an ideal alternative for individuals allergic to cow’s milk proteins. This study investigated changes in milk composition and metabolic profiles of Xinong Saanen dairy goats across four lactation stages: colostrum, early, peak, and midlactation. Conventional milk composition analysis combined with widely targeted metabolomics was applied to characterize stage-dependent metabolic variation. Milk fat, protein, lactose, solids-not-fat, and inorganic salt contents declined progressively with lactation, with significantly higher levels observed during the colostrum stage (P < 0.05). Metabolomic analysis identified 738 metabolites exhibiting distinct stage-specific patterns, among which d-glucose-1,6-bisphosphate, N1-acetylspermine, and Ser–Ile were consistently differentiated across lactation stages. Correlation analysis further revealed several metabolites significantly associated with milk composition traits. These findings provide insights into metabolic regulation underlying dynamic changes in goat milk composition during lactation and offer a basis for quality evaluation and stage-specific nutritional management.