Tracking biomolecular pathogenesis and recovery in neonatal calf diarrhea via serum infrared spectroscopy

Neonatal calf diarrhea (NCD) is an important health and economic problem in dairy cattle production because of its association with morbidity, mortality, and production losses. Moving beyond basic diagnostic classification, this study aims to track the biomolecular pathogenesis and recovery in NCD by evaluating host-level molecular damage using serum ATR-FTIR spectroscopy. Serum samples obtained from 1 to 20-day-old Holstein calves were analyzed in the mid-infrared spectral range, and the integral areas, bandwidths, and spectrochemical indices of critical bands were calculated. During the active disease phase, profound biomolecular reorganization was observed. Serum lipid acyl-chain order, packing, and mobility were severely disrupted, as evidenced by decreases in the 2922 cm^-1 band area, its bandwidth, and the A₂₉₂₂/A₂₉₆₆ and Bw₂₉₂₂/Bw₂₉₆₆ indices. Moreover, the increase in the A₁₇₄₀/A₁₅₄₀ ratio reflect a disease-induced disruption of the serum lipid-protein balance. Furthermore, a pronounced release of RNA and nucleic acid components was detected, indicated by increased PO₂^-, RNA ribose, and C-O-C band areas, as well as elevated nucleic acid-to-protein ratios (A₁₀₈₀/A₁₅₄₀ and A_(1240+1080)/A_(1650+1540)). In the recovered group, these structural and molecular aberrations systematically shifted back toward the healthy profile. ROC analyses showed that the spectrochemical parameters studied have high discriminatory potential for tracking disease activity and resolution. Overall, the findings suggest serum infrared spectroscopy as a robust, non-invasive framework not only for elucidating the molecular footprint of active pathogenesis but also for monitoring structural tissue recovery from sera in NCD.