Lactobacillus Genus Complex Probiotic-Induced Changes on the Equine Clitoral Microbiome

Dysbiosis of the lower reproductive tract (LRT) in mares may play a role in clinical diseases, including endometritis and placentitis. Metagenomic/metagenetic analysis of bacterial DNA can identify organisms that are not readily cultured and, thus, may go undetected. In this study, we tested the following hypotheses: (1) the clitoris of estrual mares harbors a unique resident microbiome, (2) topical Lactobacillus genus complex (LGC)-containing probiotic will alter the equine clitoral microbiome, and (3) early pregnancy rates following clitoral LGC application will not differ significantly from industry standards. Mares (n = 12) in estrus had sterile clitoral swabs collected (0) prior to daily topical LGC for 4 days. Second (12 h) and third clitoral swabs (48 h) were collected following final LGC application. During the next estrus, the mares were bred by artificial insemination. Genomic DNA was extracted and used for 16S rRNA sequencing via the Illumina Miseq platform. Abundance was evaluated via Friedman test with pairwise Dunn's post hoc comparisons. Statistical significance was set at p < 0.05. Compared to time 0, Desulfobacterota decreased and Corynebacterium spp. increased at 12 h and 48 h compared to 0, while Actinobacillus and Fusobacterium spp. increased in a time-dependent manner. Furthermore, Mobiluncus spp. and Christensenellacea_R-7_group decreased at 12 h and 48 h compared to 0. LGC changed the beta but not alpha diversity at both 12 h and 48 h. Mares with LGC application achieved an 85% pregnancy rate in the subsequent estrus. Future investigations are needed to understand the role of the LRT microbiome and probiotics in equine breeding.