The intestinal microbiota is essential for enhanced gut health and adequate fiber digestion. Factors such as diet transition and the stress of parturition are associated with changes in the normal microbiota of cows. Microbiota manipulation to improve performance can be achieved by the use of feed additives, such as and essential oils and vitamins, but its mechanisms of action are not completely understood. Furthermore, changes in the fecal microbiota can directly influence the vaginal microbiota of cows, which has been indicated as a major player in fertility.