Normal Parturition - Anatomy & Physiology

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Stages of Parturition

  • Stage 1: this is the preparatory stage, starting at the onset of regular uterine contractions followed by cervical dilatation and the foetus assuming the correct disposition for passage through the birth canal.
  • Stage 2: the expulsive stage, characterised by the onset of abdominal contractions which together with uterine contractions lead to foetal expulsion
  • Stage 3: separation and expulsion of the foetal membranes. In polycotous species second and third stages are often inter-mixed.

The following table summarises the normal time taken to progress through the stages of parturition in different species.

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 minutes - 4 hours 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


The step in the reproductive process that immediately precedes lactation, uterine involution and return to cyclicity. It is initiated by the foetus and involves a complex cascade of endocrine events. Parturition is the process by which the conceptus (foetus, placenta and placental membranes) is expelled from the uterus; this requires cervical softening,coordinated myometrial contractions and contraction of abdominal muscles to occur

Placental Changes

During the last 5 days of gestation, there are changes in the placenta.

  • Collaginisation of the placentome.
  • Flattening of maternal crypt epithelium.
  • Leucocyte migration and increased activity.
  • Reduction of binucleate cells in the trophectoderm.
  • Weakening of the acellular protein layer between cotyledonary and caruncular epithelium.

Contractions

  • Open endometrial crypts
  • Foetal villi have shrunk due to the escape of blood from the foetal side of the placenta when the umbillical cord ruptures.
  • Myometrial contractions aid exsanguination of the placenta.
  • Separation of foetal membranes.
  • Apex of the allantochorionic sac becomes inverted.
  • As the sac is 'rolled' down the uterine horns, foetal villi are drawn out of the crypts.
  • When a large portion becomes detached and inverted, it forms a mass in the maternal pelvis.
    • Stimulates reflex contractions of abdominal muscles.
    • Completes expulsion of the allantochorionic sac.
  • In polytocious species, dehisence and expulsion of foetal membranes are interspersed with births of the young.
    • Only expulsion of the last afterbirth stimulates abdominal contractions.
  • The final stage of allantochorionic expulsion lasts 1 hour (mare) - 6 hours (cow).
  • Domestic animals normally eat the afterbirth.
    • Not the mare or camelids.

Placental Expulsion

In most species, expulsion of foetal membranes quickly follows expulsion of the foetus.

  • After the birth of the young, regular abdominal contractions largely cease.
  • Myometrial contractions persist.
    • Decreased amplitude, but become more frequent and less regular.
    • Important for dehiscence and expulsion of foetal membranes.
  • Waves of contractions from uterus to the cervix persist.
    • Act in a peristaltic fashion in the cow and sow in the reverse direction.


Parturition Behaviour

Mare

Cow

Ewe

Sow

Bitch

Cat


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