Peripartum Disease in Dairy Cows as a Single LPS-Driven Metabolic-Immune Syndrome: Convergent Metabolomic Evidence Across Six Clinical Presentations

Six conditions of the peripartum dairy cow—ketosis, lameness, milk fever, metritis, retained placenta, and subclinical mastitis—are conventionally studied as independent diseases. Here, an integrative re-analysis of metabolomic data from one cohort studied in the author’s laboratory (University of Alberta, Edmonton, Canada), most of them previously published, spanning three biofluids (serum, urine, and milk) and four analytical platforms (DI-LC-MS/MS, GC-MS, 1H-NMR, and ICP-MS) evaluates the hypothesis that they are alternative clinical presentations of a single metabolic-immune syndrome whose proposed proximal trigger during the dry-off period is endotoxin (LPS) translocation from the involuting mammary gland, with three concurrent postpartum contributors: continuing mammary involvement and new intramammary infection; gastrointestinal LPS translocation under concentrate-rich feeding; and uterine LPS and Gram-positive lipoteichoic acid absorbed across the involuting endometrium. Four predictions were evaluated. (i) Cross-disease similarity of metabolic effect-size vectors is positive in every matrix, on two complementary serum platforms, and at every timepoint examined (mean Spearman r = 0.35–0.81, lowest postpartum and at clinical diagnosis, where partial divergence is predicted). (ii) Thirteen serum metabolites are altered in the same direction in all six disease groups eight weeks before calving, with the kynurenine/tryptophan ratio elevated 2.8–4.0-fold and completely separating every disease group from controls (p = 8.7 × 10−6, the minimum attainable for the group sizes). (iii) The urinary metabolome strengthens through the dry-off period (peak concordance at −4 wk, 44 of 91 metabolites) and partially diverges at clinical disease. The disturbance did not appear to resolve with the clinical episode: at 8 weeks postpartum, the mean absolute deviation from contemporaneous controls was similar to that observed 8 weeks before calving (mean |log2 fold change| 0.71 vs. 0.73), and the six diseases still deviated in a shared direction. (iv) Milk shows a postpartum shift consistent with TLR4 signaling (lactate and TCA-cycle intermediates up; betaine down; cobalt up in all six diseases). Comorbidity, conventionally treated as a confounder, may instead be the expected phenotype of one syndrome with multiple vulnerable-organ exits. Because the evidence is correlational and LPS was not measured, the mammary origin remains a hypothesis; direct LPS quantification, source-resolved measurements, and evaluation of competing explanations (glucocorticoid-driven reprogramming, pre-existing nutritional differences, and gut-derived signals) are required. The framework yields falsifiable predictions for dry-off-targeted, syndrome-level prevention.