Vaginal bacterial community composition and concentrations of estradiol at the time of artificial insemination in Brangus heifers

Abstract

The knowledge surrounding the bovine vaginal microbiota and its implications on fertility and reproductive traits remains incomplete. The objective of the current study was to characterize the bovine vaginal bacterial community and estradiol concentrations at the time of artificial insemination (AI). Brangus heifers (n = 78) underwent a 7-d Co-Synch + controlled internal drug release estrus synchronization protocol. At AI, a double-guarded uterine culture swab was used to sample the anterior vaginal tract. Immediately after swabbing the vaginal tract, blood samples were collected by coccygeal venipuncture to determine concentrations of estradiol. Heifers were retrospectively classified as pregnant (n = 29) vs. nonpregnant (n = 49) between 41 and 57 d post-AI. Additionally, heifers were classified into low (1.1 to 2.5 pg/mL; n = 21), medium (2.6 to 6.7 pg/mL; n = 30), and high (7.2 to 17.6 pg/mL; n = 27) concentration of estradiol. The vaginal bacterial community composition was determined through sequencing of the V4 region from the 16S rRNA gene using the Illumina Miseq platform. Alpha diversity was compared via ANOVA and beta diversity was compared via PERMANOVA. There were no differences in the Shannon diversity index (alpha diversity; P = 0.336) or Bray–Curtis dissimilarity (beta diversity; P = 0.744) of pregnant vs. nonpregnant heifers. Overall, bacterial community composition in heifers with high, medium, or low concentrations of estradiol did not differ (P = 0.512). While no overall compositional differences were observed, species-level differences were present within pregnancy status and estradiol concentration groups. The implications of these species-level differences are unknown, but these differences could alter the vaginal environment thereby influencing fertility and vaginal health. Therefore, species-level changes could provide better insight rather than overall microbial composition in relation to an animal’s reproductive health.

A Review of the Diversity of the Genital Tract Microbiome and Implications for Fertility of Cattle

“…Results from another study indicated that unclassified Enterobacteriaceae (21.05%), Ureaplasma (4.37%), and unclassified Bacteroidaceae (2.49%) were the most predominant [17]. At the phyla level, Tenericutes (36%), Proteobacteria (30%), Fusobacteria (7.6%), and Firmicutes (1.8%) were the most abundant [47]. In the study by Deng et al (2019), Firmicutes (31.57%), Proteobacteria (24.08%), Bacteroidetes (12.96%), and Tenericutes (4.95%) were the most prevalent in the vagina.…”

“…A comparison of the results from these two recent studies reveals that the proportions of the predominant microbial populations differ significantly between individuals. Phylum: Tenericutes (36%), Proteobacteria (30%), Fusobacteria (7.6%), and Firmicutes (1.8%) [47].…”

“…Microbes are very sensitive to acidic milieu; therefore, it is thought that when there are greater estradiol concentrations, there will be effects on the microbiome in the genital milieu of some species, with effects varying as a result of estradiol concentrations ( Figure 1 ). Results from a recent study indicated that Bacteroidete spp., Histophilus somni, Actinobacillus seminist, and unclassified Fusobacterium populations increase when there are relatively lower estradiol concentrations in the vaginal milieu ( Table 1 ) [ 47 ]. When there are relatively higher estradiol concentrations in the vaginal milieu, unclassified Pasteurellaceae are the predominant microbes in the vagina.…”

Ewe Vaginal Microbiota: Associations With Pregnancy Outcome and Changes During Gestation

“…Some of these factors, especially pH, can directly affect important aspects of reproduction such as sperm motility, fertilization rate, and early embryonic development and survival (Wang et al, 2020;Ravel et al, 2021). Only a handful of studies have offered insights into the vaginal microbial communities within ruminants (Swartz et al, 2014;Laguardia-Nascimento et al, 2015;Deng et al, 2019;Messman et al, 2020) and associated those findings with different reproductive outcomes (Swartz et al, 2014;Deng et al, 2019;Messman et al, 2020). Compared with other ruminants, knowledge about the microbial communities in the reproductive tract of sheep is even less.…”

Contrasting Vaginal Bacterial Communities Between Estrus and Non-estrus of Giant Pandas (Ailuropoda melanoleuca)

“… Nugeyre et al (2019) reported that progesterone can affect the abundance of some microorganisms in the vagina of female cynomolgus macaques. Messman ( Messman et al, 2020 ) reported that estradiol had a certain effect on the bacterial composition of Brangus heifers vagina. However, the corresponding relationship between hormones and vaginal microbiome in giant pandas still needs to be revealed by further study.…”