Physiology and anatomy of reproduction


Calves grow very fast in the three months of pregnancy and the end of pregnancy the fetus shifts position in the uterus and its head lies between the front feet and points toward the cervix. During normal birth the front feet and head are delivered first. Relaxation of the pelvic ligaments occurs during gestation and a marked relaxation ca be seen visually shortly before calving by a dropping of the tailhead. Shortly before calving the cervix and vagina enlarge. The cervix starts to open, and a partial decalcification of the pelvic bones occurs in order to enlarge the birth canal. As explain above, these events are under the control of the hormone relaxin. At calving the fetus is pushed from the uterus through the cervix and vagina by the contractions of the muscles in the walls of the uterus (myometrium) and by some conscious straining of the abdominal walls by the cow. The oxytoxin is responsible by the contractions of the uterine walls.

A calf at birth lacks diseases protection because antibodies (immunoglobulins) do not pass across the placenta from the dam to the circulatory system of the fetus. Then the calf needs to drink the first milk produced by the cow, which is high in nutrients and antibodies. This milk is the colostrum. Two liters of colostrum should be fed within 4 hours after birth (ideally within 30 minutes). Time is critical because the calf's digestive tract allows antibodies (large protein molecules) to pass directly into the blood within being broken down for only 24 hours. After 24 hours, antibodies cannot be absorbed intact by the small intestine (called closure).

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