Although the exact stimulus that initiates parturition is unknown, it does involve hormonal changes in both the cow and fetus as well as mechanical and neural stimulation in the uterus. Calf rotates to upright position. Uterine contractions begin. Water sac expelled. Cow usually tying down.
Fetus enters birth canal.
Front feet and head protrude first. Calf delivery completed. Uterine contractions expel membranes. During pregnancy, the fetal calf is normally on its back. This position provides the least resistance during birth.