External factors influencing reproductive tract microbiota in cattle.

Historically, bacteria identified within the reproductive tract of cattle using culture-based techniques were associated with disease. Indeed, bacterial genera including Fusobacterium, Bacteroides, Prevotella, and Porphyromonas identified by sequencing technology within the reproductive tract are indicative of the development of postpartum reproductive diseases including metritis and clinical endometritis. However, alongside culture-based methods and disease diagnosis, recent sequencing technology and bioinformatic analyses have also expanded our understanding of normal, healthy reproductive tract microbiota in cattle. Recent evidence suggests that microbiota in the reproductive tract may also play a vital role in fertility. Therefore, this review highlights our current understanding of microbiota in reproductive tissues such as the vagina, cervix, uterus, and placenta in cattle as well as describes factors such as estrous synchronization/hormonal influence, heat stress, and diet/nutritional status on shifting the composition of the reproductive tract microbiota.