Scientists delve into the bacteria within the reproductive tract of mares

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The diversity and composition of the equine vaginal microbiota were found to remain stable throughout the estrous cycle in a group of healthy Arabian mares.

Knowing which bacteria dominate vaginal microbiota and its variation throughout the cycle is important in determining how to prevent reproductive diseases.

In women, vaginal microbiota is dominated by Lactobacillus. Changes to the diversity and composition of the vaginal microbiome due to fluctuations in estrogen levels have been widely described.

However, in other mammals, these lactic acid bacteria do not dominate vaginal microbiota, but shifts of dominant microorganisms are known to occur during the ovarian cycle.

Overall, little is known about equine vaginal microbiota, Marta Barba and her colleagues at Cardenal Herrera-CEU University in Spain noted in the open-access journal, Animals.

They set out to describe the dynamics of equine vaginal microbiota during the ovarian cycle.

Eight healthy adult Arabian mares were used in the study, with vaginal swabs taken during estrus and diestrus. Two methods were used, one involving cultures and the other using RNA analysis, to identify the bacteria present.

The abundance of Lactobacillus was less than 2% by both methods, meaning that equine vaginal microbiota was not dominated by these bacteria. Lactobacillus comprised only 0.18% of the taxonomic composition in estrus and 0.37% in diestrus.

The core equine vaginal microbiome consisted of Firmicutes, Bacteroidetes, Proteobacteria and Actinobacteria at the phylum level. At the genus level it was defined by Porphyromonas, Campylobacter, Arcanobacterium, Corynebacterium, Streptococcus, Fusobacterium, uncultured Kiritimatiaellae and Akkermansia.

The results suggested that equine vaginal microbiota remained stable throughout the cycle, with no differences in the relative abundance of the most abundant bacteria observed between estrus and diestrus samples.

Discussing their findings, the authors noted that the vaginal microbiome reported in their study showed similarities with the equine fecal microbiome in the lower gastrointestinal tract described in another study.

The similarities, they said, gave rise to the view that colonization of the vaginal tract occurs mainly by fecal contamination.

In their study, no differences in microbiome composition were observed depending on ovarian cycle phases, which they said had never been reported before for mares.

“In mares, vaginal pH is very close to neutral, while vaginal pH in women is low, probably due to Lactobacillus species’ predominance in the vaginal microbiota.

“Furthermore, vaginal pH decreases when there is high estrogen concentration (follicular phase and ovulation) in women. In contrast, a decrease in vaginal pH was detected in one study the day of ovulation in mares, when estrogen concentration is low. However, no differences in pH in the rest of the estrus period were observed compared to diestrus.

“The lack of changes in pH in estrus compared to diestrus is in agreement with the lack of changes in microbial diversity and microbiome composition observed between these phases in our study,” they said.

It is possible, they added, that factors such as age, history of foal births, and level of activity could influence individual microbiome variations, but studies would be needed to determine this.

The researchers said their work supported the investigation of the vaginal microbiome as significant variations probably pointed to disease or stress generated by reproductive procedures, rather than hormonal influence throughout the cycle. However, this needed to be confirmed.

“Furthermore, the results of this study could be used to select potential probiotic bacteria that are shown to be part of dominant flora in a healthy status.”

The study team comprised Barba, Rebeca Martínez-Boví, Juan José Quereda, María Lorena Mocé, María Plaza-Dávila, Estrella Jiménez-Trigos, Ángel Gómez-Martín and Empar García-Roselló, all with Cardenal Herrera-CEU University; and Pedro González-Torres and Belén Carbonetto, who are with Microomics Systems S.L. in Barcelona.

Barba, M.; Martínez-Boví, R.; Quereda, J.J.; Mocé, M.L.; Plaza-Dávila, M.; Jiménez-Trigos, E.; Gómez-Martín, Á.; González-Torres, P.; Carbonetto, B.; García-Roselló, E. Vaginal Microbiota Is Stable throughout the Estrous Cycle in Arabian Maress. Animals 2020, 10, 2020.

The study, published under a Creative Commons License, can be read here.

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