Evaluation of the relationship between different passive transfer immunities and serum proteomes in neonatal calves.

Neonatal calf health critically depends on successful passive transfer of immunity (PTI) via colostrum. Although PTI is routinely assessed by serum IgG concentration, associated systemic proteomic responses remain poorly defined. This study aimed to relate distinct PTI categories to neonatal calf serum proteomes and to evaluate colostrum proteomes to identify proteins influencing passive transfer success. Forty Holstein cow-calf pairs were enrolled. Calf serum was collected before colostrum feeding (0 h) and at 48 h. Serum IgG was quantified by ELISA, and calves were classified at 48 h as failed (FPTI, <1000 mg/dL, n = 11), adequate (APTI, 1000-2000 mg/dL, n = 11), or excellent (EPTI, >2000 mg/dL, n = 18). For proteomic analyses, five calves were purposefully selected in each group; serum samples were pooled by PTI group and time point, and colostrum samples by PTI group, then analyzed by LC-MS/MS in DIA mode. Proteomics identified 54 proteins in colostrum and 80 in serum, 27 of which were shared between matrices. Post-colostrum intake, 21 (FPTI), 5 (APTI), and 30 (EPTI) serum proteins changed significantly from 0 to 48 h. In EPTI calves, haptoglobin (Hp) (51.10-fold) and pigment epithelium-derived factor (PEDF) (27.24-fold) showed the strongest upregulation. At 48 h, lipopolysaccharide-binding protein (LBP) and haemoglobin subunit epsilon (Hb-ε) were lower in EPTI, whereas PEDF, polymeric immunoglobulin receptor (PIGR), and SERPINA3-6 were higher, consistent with coordinated activation of acute-phase, mucosal/transport, and protease-antiprotease pathways. These findings indicate that PTI involves coordinated proteomic changes beyond IgG alone and highlight candidate biomarkers of successful passive immunity in neonatal calves.