Pregnancy Recognition
Every species is different
- Cows
- the trophoblast cells in the embryo send out bIFN-T (bovine interferon T) which provide a signal that blocks luteolysis or blocks the oxytocin receptors.
- The critical period of recognition in the cow is 15-16 days after ovulation.
- Ewe
- the trophoblast cells in the embryo send out oIFN-T (ovine interferon T) which provide a signal that blocks luteolysis or blocks the oxytocin receptors.
- The critical period of recognition in the ewe is days 13-14 after ovulation.
- Mares
- The conceptus must migrate from one uterine horn to the other, 12-14 times per day, on days 12,13, and 14 in order to inhibit PGF. This migration is necessary for recognition because the equine conceptus does not elongate as in other species. Therefore, there is less contact between the conceptus and the endometrial surface.
- The critical period of recognition in the mare is days 12-14 after ovulation.
- Sow
- The conceptus of the sow secretes estradiol which acts as the signal for maternal recognition. PGF is being produced as well but the E2 reroutes it into the lumen of the uterus causing it to have little access to circulation and then cannot cause luteolysis.
- Important to remember about the sow is that there has to be at least two conceptuses present in each uterine horn for her to maintain pregnancy. It probably has something to do with the need of a certain threshold of E2 to reroutes the PGF.
- The critical period of recognition in the sow is day 11-12 after ovulation.
- Dogs and Cats
- In the dog, there is no recognition because their CL's life spans end near the end of their normal gestation length.
- In the cat, since they are induced ovulators, if they get bred then a CL forms and its life span is the same as the queens gestation length so no recognition is needed.
- Woman
- The conceptus begins to secrete a hormone; Human Chorionic Gonadotrophin (hCG). This is a LH like hormone that acts on the C.L. to inhibit luteolysis. This is what pregnancy tests are testings for
- The critical period of recognition in woman is day 7-12 after ovulation
Placentation
Placenta is the organ that allows the nutrients of the mother to exchange with the developing fetus. They DO NOT swap blood
Extraembryonic Membranes of the Pre-attached Embryo
Amnion- layer around the fetus
Yolk Sac- shrinks, it is just temporary
Allantois-
Chorion-
Allontochorion= the last two layers fuse together and this is the fluid sac you see first when a cow is calving
The chorion produces the hormone Equine Chorionic Gonadotrophin (eCG) in mares
Types of Placenta's:
- Diffuse Placenta
- Pig- nutrient exchange points all over the placenta
- Mare- microcotyledons are really small nutrient exchange points
- Zonary Placenta
- Dogs and cats-
- Discoid Placenta
- Primates- the nutrient exchange point is a big fat disc that comes after the baby attaches on the side of the uterus. Problems occur if the disc develops over the cervical opening-no way for the baby to get out but through it.
- Cotyledon Placenta
- Cow and giraffe- convex
- Sheep and goats- concave
- The nutrient exchange points occur when the cotyledons form on the placental side and the caruncles form on the maternal side. Together these "buttons" are called placentome. They keep growing for the full duration of the gestation and they are about the size of a dime at 100 days of pregnancy. Sometimes the placenta/afterbirth will hang in the uterus after the calf is expelled because these nutrient exchange connections are still attached.
Gestation
Parturition
The Fetus
