Effects of Saccharomyces cerevisiae boulardii CNCM I-1079 on immune phenotype during the periparturient period.

Abstract

This study aims to characterize systemic and colonic intestinal mucosal immune phenotype in dairy cows across the periparturient period, and to determine whether Saccharomyces cerevisiae boulardii CNCM I-1079 (SCB) supplementation affects those components. Holstein cows (n = 83) were blocked by parity and randomly assigned to either control (CON; n = 43) or SCB (n = 40; targeted supplementation: 1.0 × 10¹⁰ cfu/cow/d of SCB top dressed) dietary treatments from d -28 prepartum to d 70 postpartum. Blood samples were collected on d -30, -7, 7, 21 and 70 relative to calving and colon biopsies at d -30, 7 and 70. Peripheral blood mononuclear cells (PBMCs) and intraepithelial leukocytes (IELs) were isolated from blood and colon biopsies, respectively, and analyzed by flow cytometry to assess T and B cell subsets, macrophages and dendritic cells. Pre and postpartum data were analyzed separately using linear mixed effect models, with fixed effects of treatment, day and its interaction, and the random effect of cow within block, and day -30 as covariable. Independent of treatment, several myeloid and lymphoid populations changed during early lactation. In blood, the proportion of CD4⁺ T cells declined from d 7 to d 21 and then recovered by d 70, whereas CD28 expression on CD4⁺ T cells peaked at d 7 and subsequently decreased, indicating early transient activation. Cytotoxic CD8⁺ T cells increased in proportion from d 7 to d 21 and remained elevated through d 70. Class-switched (IgG⁺) B cells progressively upregulated CD21 expression from d 7 through d 70, suggesting maturation and enhanced complement-responsiveness later in lactation. Within the colonic intestinal mucosa, dendritic cells were most abundant at d 7, consistent with heightened early postpartum antigen presentation. Supplementation with SCB selectively enhanced humoral activation postpartum, reflected by increased CD86 expression on both naïve (IgM⁺) and class-switched (IgG⁺) B cells. Together, these findings indicate that immune changes during the periparturient period reflect a transient immune activation at immediate postpartum rather than overall suppression, and that SCB supplementation may enhance B cell activation and support immune function during early lactation.