Sources of Progesterone during Gestation

Sources of progesterone during gestation vary significantly among animal species, but most of time it is corpus luteum and placenta only.

This table shows various animal species and their progesterone sources:

In addition to progesterone, estrogens are also secreted by the placenta, particularly during the last part of gestation. The peak estrogen in most species signals early preparturient period.

Placental lactogen is Protein hormone – 192 AA; 22,000 and 23,000 daltons; Important for its GH like properties; Regulation of maternal nutrients and fetal growth. It has been hypothesized that, sire can influence the fetal placental lactogen and enhance milk production.

Pregnancy specific protein Prevents destruction of CL; First reliable hormonal pregnancy test.

Placental relaxin is produced in mares, cats, bitches, sows, rabbit, monkeys and humans. In rabbit the relaxin is produced completely from the placenta and not from the ovary.

Relaxin is not present in bovine placenta during any stage of gestation a possible exception is that ovariectomy does not result in calving difficulties. It is likely that relaxin is produced from ovary and placenta except in rabbits.