Normal Parturition - Anatomy & Physiology

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Placental Expulsion

  • 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.



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