Upon passage through the vulva, the umbilical cord generally breaks, and the lungs become functional. Delivery is normally completed in one hour or less. Special assistance is warranted if this stage goes beyond two to three hours. The caruncle-cotyledon, or button attachment between uterus and placenta, relaxes and separated after parturition. The placenta is then expelled by continued uterine contractions.
Cows normally expel the placenta within two to eight hours.
Preparing for Calving Assistance Normal delivery should be completed within two to three hours after the water sac appears in heifers, and one to two hours in cows. If prolonged, the calf may be born dead or in a weakened condition. Since timing is vital to providing proper assistance, frequent observations are a must. Assisted deliveries should not be attempted without proper preparation of facilities and equipment. A clean, well-lighted maternity stall with head catch facilitates examination.