Yeast product supplementation modulated humoral and mucosal immunity and uterine inflammatory signals in transition dairy cows.

The transition from late gestation to early lactation is characterized by substantial metabolic stress and altered immune function. The objective of this study was to assess the effects of supplementing a yeast product derived from Saccharomyces cerevisiae on immunity and uterine inflammation in transition cows. Forty multiparous Holstein cows were blocked by expected parturition date and randomly assigned within block to 1 of 4 treatments (n=10) from 21d before expected parturition to 42d postpartum. Rations were top-dressed with a product containing yeast culture plus enzymatically hydrolyzed yeast (YC-EHY; Celmanax, Vi-COR, Mason City, IA) at the rate of 0, 30, 60, or 90g/d throughout the experiment. Cows were injected subcutaneously with ovalbumin on d -21, -7, and 14 to assess their humoral response. Data were analyzed using mixed models with repeated measures over time. Concentrations of colostrum IgG were unaffected by treatments. A treatment × week interaction was observed for somatic cell linear score, reflecting a tendency for a quadratic dose effect on wk 1 (2.34, 2.85, 1.47, and 4.06±0.59 for 0, 30, 60, and 90g/d, respectively) and a quadratic dose effect on wk 5 (1.36, -0.15, -1.07, and 0.35±0.64 for 0, 30, 60, and 90g/d, respectively). Platelet count was increased by YC-EHY. Increasing YC-EHY dose linearly increased plasma anti-ovalbumin IgG levels following 3 ovalbumin challenges, suggesting that treatments enhanced humoral immunity. Increasing YC-EHY dose also quadratically increased fecal IgA concentrations in early lactation, suggesting that 30 and 60g/d doses enhanced mucosal immunity. Uterine neutrophil populations were much greater in samples collected on d 7 compared with those on d 42 (32.1 vs. 7.6±3.5% of cells), reflecting neutrophil infiltration immediately after calving, but no treatment effect was detected. Significant day effects were detected for mRNA of IL-6, IL-8, neutrophil myeloperoxidase (MPO), and neutrophil elastase (ELANE) in the uterine samples, reflecting greater abundance of these transcripts collected on d 7 compared with d 42. A quadratic dose effect was detected for IL-6, indicating that 30 and 60g/d doses decreased uterine IL-6 mRNA. The mRNA abundance of MPO and ELANE was increased linearly by YC-EHY. Supplementation with YC-EHY enhanced measures of humoral and mucosal immunity and modulated uterine inflammatory signals and mammary gland health in transition dairy cows.