Corpus Luteum function and parturition in cattle and pigs

At term pregnancy in cattle and pigs progesterone is from luteal origin. Li ke in other domestic animal species, parturition in the cow and pig is prec eeded by a sudden drop in the maternal plasma progesterone concentration. A n increased output of prostaglandin from the pregnant uterus is most likely responsible for prepartum luteolysis. ne withdrawal of progesterone is not immediately followed by activation of the myometrium; rather a period of ( relative) myometrial quiescence allows for functional changes to take place in the cervix and myometrium, before parturient uterine contractions devel op (between 12 and 14 hours, and between 6 and 9 hours before onset of the expulsive stage, in cows and pigs respectively). These will only subsequent ly cause a widening of the cervix. Maintenance of progesterone dominance, by treatment with exogenous progcste rone/ progestagens or by induction of a new set of corpora lutea (pigs), at the time that parturition is initiated, will postpone delivery. However, u terine prostaglandin output (cows) still increases under these conditions ( cows) and many of the calves and piglets are born dead when (prolonged) exp ulsion finally takes place after relief from progesteron. This indicates th at progesterone is not able to counteract completely the parturition promot ing signals generated by the pregnant uterus.