9 Relationship Between Progesterone and Reproductive Tract Microbiota in Pregnant Gilts
Authors: Stockland Erin , Hickman-Brown Kyle J , Smith Molly S , McAnally Brooke E , Cain Joe , Seo Heewon , Bazer Fuller W , Johnson Greg , Wiegert Jeffrey G , Poole Rebecca K 
Published: May 2023

Abstract
Female reproductive performance is essential for economic profitability of swine operations, and sex steroid hormones, such as progesterone (P4), are necessary for proper reproductive function. Recent research targeting the reproductive microbiome in beef cattle found that as P4 concentrations fluctuate during the estrous cycle, bacterial communities in reproductive tissues also change. However, characterizing the relationship between P4 concentrations and bacterial communities within the reproductive tract has yet to be fully determined in swine. Therefore, the objective of this project was to correlate the abundance of reproductive tract bacterial communities with plasma P4 concentrations from pregnant gilts. Duroc X Landrace X Yorkshire gilts (n = 25), free of any physical or health related issues, were euthanized and hysterectomized on days (d) 11 (n = 7), 15 (n = 6), 60 (n = 6) or 90 (n = 6) of gestation. For microbiome evaluation, sterile swabs were individually rotated 8 times on each tissue and immediately placed in sterile microcentrifuge tubes for storage (-80°C) until sequencing. Allantoic and amniotic fluid collected on d 60 and d 90 of gestation was placed immediately in a sterile 10 mL conical tube and stored (-80°C) for subsequent analyses. Blood was collected concurrently, centrifuged at 2,500 x g for 25 min at 4°C, and the resulting plasma stored (-20°C). Concentrations of P4 in plasma were quantified using a double-antibody RIA kit. Bacterial sequencing of the V4 hypervariable region of 16S rRNA gene was completed by FERA Diagnostics and Biologicals Corp. The data were analyzed statistically using PROC CORR in SAS 9.4. In the cervix, the relative abundance of the phylum Firmicutes was positively correlated with P4 concentrations (r = 0.45, P = 0.03), and within this phylum, genus Lactobacillus was positively correlated with P4 concentrations (r = 0.54, P = 0.01). Phylum Bacteroidetes was negatively correlated with P4 concentrations (r = 0.45, P = 0.03), and within this phylum, genera Prevotella and Bacteroides were also negatively correlated with P4 concentrations (r = -0.49, P = 0.01; r = -0.05, P = 0.01, respectively). In the uterus, plasma P4 tended to be negatively correlated with phylum Proteobacteria (r = -0.37; P = 0.07) yet positively correlated with Phylum Firmicutes (r = 0.40; P = 0.05). Within Firmicutes, genus Streptococcus in the uterus was positively correlated with P4 concentrations (r = 0.50, P = 0.01), and the relative abundances of genus Lactobacillus in both the uterus and allantoic fluid were positively correlated with concentrations of P4 in plasma (r = 0.43, P = 0.04; r = 0.70, P = 0.02, respectively). There were no significant correlations between concentrations of P4 in plasma and abundances of bacteria within the vagina or amniotic fluid. These results indicate that shifts plasma P4 influence microbiomes in reproductive tissues of gilts during gestation. Further investigation is necessary to understand the interplay between P4 and microbiome fluctuations within reproductive tissues in swine.