Difference between revisions of "Normal Parturition - Anatomy & Physiology"

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* Domestic animals normally eat the afterbirth.
 
* Domestic animals normally eat the afterbirth.
 
** Not the mare or camelids.
 
** Not the mare or camelids.
 
 
 
 
 
 
 
 
 
 
 
* Expulsion of the foetus requires that the chorionic villi become dislodged from the crypts of the maternal side of the [[Female_Reproductive_Tract_-Placenta_-_Anatomy_%26_Physiology|placenta]].
 
** Brought about by powerful vasoconstriction of arteries in the villi.
 
*** Vasoconstriction reduces pressure and allows villi to be released from crypts.
 
 
  
  

Revision as of 09:51, 4 August 2008

BACK TO REPRODUCTIVE SYSTEM
BACK TO PARTURITION



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.

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.


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