Longitudinal characterization of the adipose tissue metabolome in dairy cows during the transition from cessation to resumption of lactation.

Dairy cows undergo profound metabolic challenges as they transition from lactation cessation to lactation resumption. Adipose tissue (AT), serving as the primary energy reserve and an active endocrine organ, plays a crucial role in these adaptations. Thus, the objective of the current study was a comprehensive characterization of the metabolic changes in the AT metabolome of Holstein dairy cows as they transitioned from one lactation cycle to the next, providing key insights into the dynamic adaptations crucial for maintaining energy homeostasis and optimizing lactational performance. Twelve Holstein dairy cows (BW = 745 ± 71 kg, BCS = 3.43 ± 0.66), housed in tiestalls, were dried off 6 wk before their expected calving date (mean dry-off time = 42 d). Cows were individually fed ad libitum TMR, consisting of grass silage, corn silage, and concentrate during lactation and a mixture of corn silage, barley straw, and concentrate during the dry period. The metabolome was characterized in subcutaneous AT samples collected on wk -7 (before drying off), -5 (after drying off), and wk -1 and 1 relative to calving. A targeted metabolomics approach was employed using the MxP Quant 500 kit (Biocrates Life Sciences AG), integrating liquid chromatography, flow injection, and electrospray ionization triple quadrupole MS. Statistical analysis of the AT metabolite data was conducted using MetaboAnalyst 5.0, enabling various multivariate analyses, including principal component analysis, partial least squares discriminant analysis, hierarchical clustering, and the generation of informative heatmaps. Multivariate analyses revealed distinct and dynamic alterations in the AT metabolome, with minimal changes during the early dry period (wk -7 to -5) followed by pronounced metabolic reprogramming close to calving (wk -1 to 1). Amino acid profiles in AT remained stable during late gestation but declined significantly in Ala, Asp, and Gln between wk -1 and wk 1, likely due to increased utilization within AT, redirecting carbon skeletons from these AA toward glyceroneogenesis and the re-esterification of fatty acids (FA) into triglycerides. Such a shift in AA metabolism may also facilitate interorgan nutrient exchange, with Ala export through the glucose-Ala cycle providing essential gluconeogenic substrates to the liver during early lactation. Moreover, acylcarnitine profiles remained unchanged, reflecting the role of AT as a long-term lipid reservoir rather than a metabolically active site for FA oxidation. The data revealed a biphasic pattern in diglycerides and extensive remodeling of phosphatidylcholines, underscoring dynamic cellular membrane adaptations to heightened lipolytic activity and increased energy demands during the immediate postpartum period. Notably, sphingomyelin remained stable throughout the transition, suggesting potential mechanisms in preserving membrane integrity and ensuring cellular stability under fluctuating metabolic stress. Together, these data further support that AT functions not merely as a passive energy store but as a dynamic organ actively orchestrating metabolic homeostasis during the transition from lactation cessation to lactation resumption.