Latent inflammatory activity is associated with alterations in iron bioavailability during early postpartum...

The transition from late gestation to early lactation is accompanied by profound metabolic and immunological adaptations in dairy cows. While the relationship between inflammation and iron metabolism has been extensively studied in clinical diseases, less is known about how physiological or low-grade inflammatory processes influence iron bioavailability during early lactation. This study investigated associations between inflammatory activity and indicators of iron bioavailability in dairy cows during the early postpartum period, with particular emphasis on the use of a latent inflammatory index derived by principal component analysis (PCA).

Twenty clinically healthy dairy cows were monitored on Days 0, 3, 7, 14, and 21 postpartum. Blood serum concentrations of inflammatory markers (IL-1, IL-6, TNF-α, IFN-γ, haptoglobin, serum amyloid A, and extracellular HSP70) and iron-related parameters (Fe, TIBC, UIBC, and transferrin saturation, TS%) were determined. Temporal changes were evaluated using multivariate analyses, correlation analysis, PCA, and linear mixed-effects models.

Iron-related parameters declined during early lactation, reaching minimum values around Day 7, followed by partial recovery by Day 21. In contrast, inflammatory markers exhibited a transient increase, peaking between Days 3 and 7 before gradually returning toward baseline. Multivariate clustering and heatmap analyses revealed a clear temporal separation between the inflammatory activation phase and the recovery phase, indicating an inverse relationship between inflammatory status and iron bioavailability. Correlation analysis confirmed significant negative associations between inflammatory mediators, particularly IL-6 and haptoglobin, and all iron metabolism indicators. Because of substantial multicollinearity among inflammatory variables, PCA was applied to generate a latent inflammatory score. The first principal component (PC1-infla) explained 63.5% of the total variance and represented overall systemic inflammatory activity. Linear mixed-effects models demonstrated that higher PC1-infla scores were significantly associated with lower Fe, TIBC, UIBC, and TS% values (p < 0.001).

PC1-infla was consistently associated with markers of iron bioavailability and showed the strongest statistical association with iron-related biomarkers among the evaluated inflammatory variables. These findings indicate that early postpartum adaptation in dairy cows is characterized by coordinated inflammatory activation accompanied by reduced iron bioavailability. The overall inflammatory burden appears to play a greater role in regulating iron metabolism than individual inflammatory markers alone.