The healthy equine uterus harbors a distinct core microbiome plus a rich and diverse microbiome that varies with geographical location

Abstract

The goal of this study was to understand the composition and existence of the resident uterine microbiome in healthy mares and to establish the presence of a core microbiome for the healthy equine uterus. We analyzed the microbiomes of 35 healthy mares that are long-time residents of three farms in Oklahoma, Louisiana, and Australia as well as that of 19 mares purchased from scattered owners in the Southern Mid-Western states of the United States. Over 6 million paired-end reads of the V4 region of the 16S rRNA gene were obtained resulting in 19,542 unique Amplicon Sequence Variants (ASVs). ASVs were assigned to 17 known phyla and 213 known genera. Most abundant genera across all animals were Pseudomonas (27%) followed by Lonsdalea (8%), Lactobacillus (7.5%), Escherichia/Shigella (4.5%), and Prevotella (3%). Oklahoma and Louisiana samples were dominated by Pseudomonas (75%). Lonsdalea (28%) was the most abundant genus in the Australian samples but was not found in any other region. Microbial diversity, richness, and evenness of the equine uterine microbiome is largely dependent on the geographical location of the animal. However, we observed a core uterine microbiome consisting of Lactobacillus, Escherichia/Shigella, Streptococcus, Blautia, Staphylococcus, Klebsiella, Acinetobacter, and Peptoanaerobacter.

Metagenomic analysis unravels novel taxonomic differences in the uterine microbiome between healthy mares and mares with endometritis

“…The detection of a diverse uterine microbiome in healthy mares in the present study, together with the findings of previous studies (Heil et al, 2018; Holyoak et al, 2022), strongly refutes the dogma of a sterile uterus in healthy mares. The composition of the uterine microbiome in the healthy mares in this study was mostly similar to that reported in a previous study in horses (Holyoak et al, 2022) and studies in other domestic animal species such as cows (Clemmons et al, 2017; Moore et al, 2017) and dogs (Lyman et al, 2019). Similar to the findings of Holyoak et al (2022), proteobacteria and firmicutes constituted a vast majority of the uterine microbiome.…”

“…The composition of the uterine microbiome in the healthy mares in this study was mostly similar to that reported in a previous study in horses (Holyoak et al, 2022) and studies in other domestic animal species such as cows (Clemmons et al, 2017; Moore et al, 2017) and dogs (Lyman et al, 2019). Similar to the findings of Holyoak et al (2022), proteobacteria and firmicutes constituted a vast majority of the uterine microbiome. However, there were some differences at the genus and species levels, which could be attributed to different geographical locations.…”

“…Similar to the findings of Holyoak et al (2022), proteobacteria and firmicutes constituted a vast majority of the uterine microbiome. However, there were some differences at the genus and species levels, which could be attributed to different geographical locations.…”

“…The dogma that the healthy uterus is sterile has been challenged by research studies conducted in various species including cattle (Moore et al, 2017), horses (Heil et al, 2018; Holyoak et al, 2022), and dogs (Lyman et al, 2019). Several bovine studies have demonstrated that the uterine microbiome is dynamic with remarkable differences reported between a healthy state and disease conditions such as endometritis (Bicalho et al, 2017; Pascottini et al, 2020; Ballas et al, 2021).…”

Isolated Bacteria from the Uteri of Camels with Different Reproductive Backgrounds: A Study on Sampling Methodology, Prevalence, and Clinical Significance

“…Different parts of the reproductive tract in mammals have been shown to harbor their own distinct microbiota and a wide variety of opportunistic and pathogenic bacteria [ 1 ]. In large animals, uteri can potentially be contaminated with considerable loads of microorganisms during late gestation and throughout the postpartum period, and the respective phyla can fluctuate during the following periods and at different times of the estrous cycle [ 2 , 3 ]. The contaminating bacteria may or may not underpin uterine infections depending mainly on the type and number of the bacteria, presence of virulence factors and the host response to contamination [ 4 , 5 , 6 ] and should infection develop, they could eventually lead to significant reproductive losses by adversely affecting the follicular growth [ 7 , 8 ], conception rate and embryo survival [ 9 , 10 ] and disturbing normal hormonal profile of the affected animals [ 11 ].…”