Normal Parturition - Anatomy & Physiology
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- The Process by which the conceptus (foetus, placenta and placental membranes) are expelled from the Uterus requires:
- Cervical Softening
- Coordinated Myometrial Contraction
- Voluntary contraction of abdominal muscles
- In most species, expulsion of foetal membranes quickly follows expulsion of the foetus.
- Expulsion of the foetus requires that the chorionic villi become dislodged from the crypts of the maternal side of the placenta.
- Brought about by powerful vasoconstriction of arteries in the villi.
- Vasoconstriction reduces pressure and allows villi to be released from crypts.
- Brought about by powerful vasoconstriction of arteries in the villi.
| Species | Mare | Cow | Ewe | Sow | Bitch |
|---|---|---|---|---|---|
| Stage 1: Contractions and Cervical Dilation | 1-4 hours | 2-6 hours | 2-6 hours | 2-12 hours | 6-12 hours |
| Stage 2: Foetal Expulsion | 12-30 minutes | 30-60 minutes | 30-120 minutes | 150-180 minutes | 6 hours (up to 24 hours with large litters) |
| Stage 3: Placental Expulsion | 1 hour | 6-12 hours | 5-8 hours | 1-4 hours | Placenta Exits with Foetus |