Immune-Adaptive Transcriptomic Networks Supporting Sustained Milk Production and Reproductive Longevity in Dairy Cows

In modern dairy systems, sustained milk production over the lifetime of a cow depends critically on maintaining reproductive efficiency across repeated lactation cycles. However, repeated lactation and advancing parity impose cumulative metabolic and inflammatory stress that often compromises fertility and shortens productive lifespan. Increasing evidence suggests that immune dysregulation contributes to parity-associated reproductive decline, raising the possibility that sustained milk production requires adaptive immune regulation. We hypothesized that cows achieving reproductive longevity exhibit parity-dependent immune remodeling that supports continued reproductive function and extended milk production. To test this hypothesis, we profiled blood transcriptomes from 131 Holstein cows spanning parities 1-9. Analysis of 17 422 expressed genes identified six distinct parity-associated expression trajectories, revealing coordinated transcriptomic remodeling with increasing reproductive history. Differential expression analysis identified 1 405 parity-associated genes enriched in immune- and stress-related pathways, including MAPK and Rap1 signaling. Weighted gene co-expression network analysis further identified immune-regulatory modules strongly correlated with parity and key reproductive indicators, suggesting a central role of immune adaptation in sustaining reproductive efficiency. Machine learning analysis of 256 genes in significantly enriched pathways with P-adjusted < 0.05 prioritized PDE4C, APLN, and CDH15 as potential key predictors of reproductive persistence. Integration with co-expression networks demonstrated that these genes may function as highly connected hub nodes within immune- and stress-responsive modules. Collectively, these results indicate that coordinated immune signaling networks are associated with reproductive persistence and thereby contribute to extended milk production in dairy cows. This study provides molecular insight into the immune mechanisms underlying productive longevity and identifies candidate biomarkers with potential applications in genomic selection and precision herd management.