Characterization of immune cell metabolism and systemic function during the transition period of dairy cows

Abstract

The periparturient period represents one of the most physiologically and metabolically demanding stages in the productive life of dairy cows. As animals transition from gestation to lactation, nutrient demands rise sharply while feed intake declines, resulting in a negative energy balance that can compromise immune competence and increase disease risk. While traditionally characterized as a period of immunosuppression, recent evidence indicates that the transition period is marked by immune dysregulation and overactivation, driven by concurrent metabolic and environmental stressors. This thesis aimed to provide an integrative view of immune changes in dairy cows across the periparturient period, examining systemic and mucosal adaptations in major lymphoid and myeloid cell populations, and exploring, at the cellular level, the metabolic activity of T helper cells and the potential for nutritional modulation of immune function through probiotic supplementation. In the first study, systemic and mucosal immune adaptations were characterized in Holstein cows supplemented or not with Saccharomyces cerevisiae boulardii CNCM I-1079 from three weeks before to ten weeks after calving. Blood and colon samples were collected at multiple time points, and immune cell populations were evaluated by flow cytometry. Independent of treatment, both lymphoid and myeloid cell populations changed dynamically during early lactation. The proportion of circulating CD4⁺ T cells decreased immediately after calving but recovered by 70 days postpartum, while cytotoxic CD8⁺ T cells increased and remained elevated. Within the intestinal mucosa, dendritic cells peaked at seven days postpartum, consistent with early postpartum antigen presentation. SCB supplementation enhanced humoral activation, as reflected by increased CD86 expression on both naïve (IgM⁺)

and class-switched (IgG⁺) B cells, suggesting improved immune homeostasis through nutritional support. The second study explored the metabolic and functional properties of CD4⁺ T helper cells across the periparturient period. Using Seahorse metabolic flux analysis, we found that activated T helper cells exhibited greater glycolytic and oxidative metabolism at +3 and +28 days compared to prepartum. Similarly, T helper cell proliferation and proinflammatory cytokine secretion (IL-1α, IL-1β, and IL-6) were upregulated at postpartum, while gene expression of metabolic markers remained stable. These results indicate that T helper cells are metabolically active and functionally competent after calving, displaying features of immune adaptation rather than suppression. Collectively, the studies presented in this thesis reveal that immune changes around calving reflect an adaptive reprogramming response rather than suppression. Enhanced cellular metabolism and selective activation of immune subsets likely represent physiological responses to metabolic stress and tissue remodeling after parturition. Understanding these mechanisms and identifying nutritional strategies to support immune balance may improve health, productivity, and welfare in transition dairy cows.