Normal Parturition - Anatomy & Physiology

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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



Parturition is the Process by which the conceptus (foetus, placenta and placental membranes) are expelled from the Uterus requires:


Stage 3: 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.

Parturition Behaviour

Mare

Stage 1

  • Mammary hypertrophy, waxing of the teats and possible escape of milk from the glands.
  • Patchy sweating behind the elbows and around the flanks.
    • Commences ~4 hours before the birth of the foal and increases as the stage progresses.
  • Yawns
  • No indication of pain.
  • Food is taken readily
  • Respirations are normal
  • Pulse is ~60
  • Body temperature may become slightly subnormal (36.5-37◦C).
  • Restlessness, wanders aimlessly.
  • Tail is frequently raised or held to one side.
  • May swish the tail or slap it against the anus.
  • Kicking of the abdomen
  • Towards the end of this stage:
    • Crouching
    • Straddling of hindlimbs
    • Going down on knees or sternum and rising again
    • Glancing at flank
  • This stage terminates with the rupture of the allantochorionic membrane and the escape of allantoic fluid from the vulva.
    • No visible straining during this period.

Stage 2

  • Abrupt onset, lasts~17 minutes
  • Appearance of the amnion or commencement of forceful straining
    • Not much delay between them, often coincide.
  • Soon after straining begins, the mare goes down.
  • Lies on her side with the limbs extended
    • Generally remains in this position until the foal is born.
  • Transperent blue/white 'water bag' (amnion) visible at the vulva
  • Quickly followed by the appearance in it of a digit.
  • Straining at regular intervals.
    • Each comprises 3/4 powerful expulsive efforts followed by a period of rest.
    • Generally 3 minutes long
  • One forelimb procedes the other by 7-8cm
    • One elbow passes through the pelvic inlet before the other preventing minimal obstruction.
  • Head is usually in the oblique position, but may be transverse with the cheek lying on the limbs.
  • Greates and longest effort is with birth of the head.
  • After expulsion of the foal, the mare may remain on her side exhausted for up to 30 minutes.
  • Umbillical cord is intact when the foal is born.
    • Subsequently ruptures 5-8cm below the belly due to movement of the mare or foal.
  • Foal is usually born within the amnion, which is ruptured by movements of the forelegs.
  • Lower portions of the hindlimbs often remain within the vagina for minutes after the rest of the foal is born.

Stage 3

  • Membranes expelled quickly after the birth of the foal.
  • Usually within 3 hours.
  • Duration of stage 3 is ~30 minutes.
  • Afterbirth is expelled by myometrial contractions with no straining.

Cow

Stage 1

  • Lasts ~6 hours
  • Relaxing of pelvic ligaments.
  • Mammary secretions change from transparent,honey-like to opaque, cellular colostrum.
  • Body temperature subnormal by ~0.6◦C.
  • Parturition will begin 12 hours after complete relaxation of the posterior borders of the sacrosciatic ligaments.
  • Heifers may show signs of abdominal pain for up to 24 hours before the cervix is fully dilated.
  • Occasional straining may occur.
  • Picks at feed, irregular rumination
  • 'Lowing'
  • Kicking of the abdomen
  • Restless, may stand with her back arched and tail raised.
    • May go down and rise again frequently
  • Pulse rate often increased to 80-90.

Stage 2

Stage 3

Ewe

Sow

Stage 1

Stage 2

Stage 3

Bitch

Stage 1

Stage 2

Stage 3

Cat

Stage 1

Stage 2

Stage 3

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