After the follicle ruptures into the abdominal cavity, the fimbria is positioned to catch the fertile ova.
Fertilization occurs in the fallopian tube or oviduct.
One sperm impregnates the zona pellucida forming an activated oocyte which undergoes rapid cellular divisions. The CL3 secretes P4 that stimulates the formation of uterine milk, which maintains a beneficial environment for early embryonic growth. The gestational length is influenced by and varies with the breed, the sex of the fetus, genetics of the cow and bull, environmental temperature, the number of feti and nutrition. There are 3 phases during the gestation that help in categorizing the clinical signs of reproductive diseases and understanding the effects of drugs on different periods of the pregnancy. At day 12 the second phase, the embryonic period, begins and continues until day 35 during which time dermal layers are formed, organogenesis is initiated, and placentation starts.