Alterations in serum bile acids and metabolomic profiles associated with ketosis severity in postpartum dairy cows

Abstract

Ketosis, a disorder of glucose and lipid metabolism, significantly impacts the health and performance of postpartum dairy cows. Bile acids are crucial for intestinal lipid absorption in mammals. In non-ruminants, bile acids also regulate glucose and lipid metabolism and promote hepatic lipid oxidation, suggesting a potential link to ketosis that warrants investigation in dairy cows. This study employed targeted and untargeted metabolomics to identify significant differences in serum bile acids and metabolites among control (CON; β-hydroxybutyrate (BHB) < 1.2 mmol/L, n = 14), subclinical ketosis (SCK; 1.2 ≤ BHB <3.0 mmol/L, without obvious clinical symptoms, n = 14), and clinical ketosis (CK; BHB ≥ 3.0 mmol/L, with signs including reduced appetite, milk yield, and rumination, n = 14) dairy cows. Holstein dairy cows (parities 2 to 5) were sampled between 5 and 7 days in milk (DIM). For each cow, serum samples collected over three consecutive days were pooled in equal volumes. The cows had a previous 305-day milk yield averaging 44.22 ± 9.72 kg/day. Serum biochemical and untargeted metabolomic analyses were performed in 14 cows per group, while targeted bile acid profiling was performed in a subset of 12 cows per group. The results showed a significant decrease in serum glucose concentration as ketosis severity increased, whereas BHB and nonesterified fatty acid (NEFA) concentrations and aspartate aminotransferase (AST) activity significantly increased. Targeted bile acid profiling revealed that, the CK group presented lower levels of glycocholic acid (GCA), glycochenodeoxycholic acid (GCDCA), taurolithocholic acid (TLCA), and total bile acids than the CON and SCK groups, likely reflecting the more severe metabolic and physiological derangements in these cows. The cholic acid (CA) concentration was also lower in the CK group than in the SCK group. Spearman correlation analysis revealed a significant negative association between blood BHB concentration and serum GCDCA and TLCA concentrations, suggesting their potential as candidate indicators for ketosis severity. Untargeted liquid chromatography–tandem mass spectrometry (LC–MS/MS) metabolomics revealed that ketosis profoundly altered metabolites involved in lipid and energy metabolism, inflammatory responses, and antioxidant capacity; differentially altered metabolites were defined as those with a variable importance in projection (VIP) score > 1.0 from the OPLS-DA model and a Benjamini–Hochberg false discovery rate (FDR)-adjusted P < 0.05 from Student’s t tests. Bioinformatics analysis using Progenesis QI 2.3, ropls 1.6.2, and MetaboAnalyst 5.0 with the KEGG pathway library identified key enrichment pathways, including glycerophospholipid metabolism, α-linolenic acid metabolism, tryptophan metabolism, tyrosine metabolism, and beta-alanine metabolism (hypergeometric test; FDR-adjusted P < 0.05). Notably, within the glycerophospholipid pathway, several metabolites, including Lysopc(15:0), Lysopc(22:4/0:0), and Pe-Nme2(22:6/15:0), were downregulated in both SCK and CK groups compared with CON. Overall, increasing ketosis severity was associated with coordinated alterations in glucose and lipid metabolism and in the serum bile acid profile, most notably reduced concentrations of GCDCA and TLCA, which were negatively correlated with blood BHB levels and may serve as candidate biomarkers of ketosis severity.