Impact of Pre-Existing Uterine Microbiome on Pregnancy Success After Embryo Transfer in Cattle

The uterine microbiome plays a critical role in maintaining pH balance, modulating the immune system, and influencing fertility, especially in artificial breeding contexts. This study examined the impact of uterine microbiota on pregnancy success in cows following embryo transfer (ET), using Illumina 16S rRNA gene sequencing of the V4 hypervariable region of samples collected from the uterine horn (UH) and the uterine body (UB) of cows during the estrous cycle preceding synchronization for ET in the Amazon region. Microbiomes from the uterine horn (UH) and the uterine body (UB) were analyzed before embryo transfer. Cows that became pregnant (UH-P and UB-P) and those that did not (UH-NP and UB-NP) were compared. Fifteen cows were grouped as follows: UB-P (three), UB-NP (five), UH-P (three), and UH-NP (four). Linear discriminant analysis effect size and heat tree analyses identified Sphingobacterium and Stenotrophomonas spp. as significantly enriched in the UB-P and UH-NP groups, respectively. Additionally, non-pregnant cows exhibited more distinctive genera than pregnant ones. These findings suggest that cows achieving pregnancy have lower microbial diversity and fewer potentially pathogenic genera. This study contributes to the emerging field of pre-pregnancy uterine microbiome research in cattle, offering evidence that microbial composition may influence reproductive success, and highlights specific taxa as potential biomarkers for pregnancy outcomes following embryo transfer.