Normal Parturition - Anatomy & Physiology

BACK TO REPRODUCTIVE SYSTEM BACK TO PARTURITION

• 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.

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