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

  • Lasts 30 minutes - 4 hours
    • Longer in heifers than in cows
    • Male calves take longer to be born
  • Onset marked by the appearance of the amnoin ('water bag') at the vulva.
  • Less frequent straining
  • Remains standing at first
  • During passage of the head through the vulva, the cow normally goes down and remains recumbent until the calf is born.
  • May lie on her side or in sternal recumbency.
  • Placental separation occurs more slowly than in the mare.
  • Umbillical cord of the calf is shorter than in the foal and generally ruptures as the calf falls from the vulva.

Stage 3

  • Expulsion of the foetal membranes usually occurs ~6 hours after the birth of the calf.
    • After 24 hours consider a pathological cause for retained placenta.
  • Cow will eat the foetal membranes.

Ewe

Similar to the cow, except incidence of twinning and triplets is high.

Stage 2

  • Completed within 1 hour usually.
  • Lambs nrmally in enterior presentation.
  • In twin births where one foetus occupies each horn, one horn develops contractions before the other.
    • Hence distocia due to simultaneous presentation is more common when both foetuses occupy the same horn.

Stage 3

  • Placenta usually expelled within 2-3 hours after birth of the lamb.

Sow

Stage 1

Stage 2

Stage 3

Bitch

Stage 1

  • Lasts ~ 12 hours
  • Prepares the bed
  • If carrying one pup, the onset of lactation coincides with parturition.
  • If carrying multiple pups, milk may be expressed from the teats several days prior to the onset of parturition.
  • Body temperature subnormal by at least 1.2◦C within 24 hours before the onset of labour.
  • Restless
  • Indifferent to food
  • Panting

Stage 2

  • Depends upon the number of foetuses, but usually lasts ~6 hours.
  • Straining indicates the onset of the second stage.
  • Bitch remains in her bed in sternal recumbency
  • 'Water bag' of the first foetus appears at the vulva, and attains the size of a golf ball.
  • Bitch licks the vulva vigorously and usually ruptures the 'water bag'.
  • Delivery of the head requires the greates effort, once this is bord the rest of the foetus follows easily.
  • Expulsion of the first foetus may take up to 1 hour.
  • Umbillical cord is intact at birth, the mother will soon bite it away.
  • Bitch rests for a time after the birth of the first puppy.
    • Lies licking the puppy, which soon begins to suckle.
    • Pays frequent attention to the vulva and licks any discharge.
  • Foetal membranes generally voided in 10-15 minutes and eaten by the bitch.
  • Straining recommences after a delay of 30 minutes - 2 hours.
  • Effort and time required for subsequent deliveries is usually less than the first.
  • May rest in between subsequent deliveries, but may not. The period of rest is also very variable.
  • Puppies tend to be expelled from alternate horns (unlike the sow).
  • Expulsion of foetal membranes is also irregular, they may come out individually, or the next puppy may be born with the membranes of its predeccessor around its neck.

Stage 3

  • Membranes of the last foetus are expelled with it or shortly afterwards.
  • Discharge is dark green in colour.
    • Due to breakdown of the marginal haematoma, blood pigment biliverdin escapes.

Cat

During the last week of pregnancy, the queen seeks a nesting area. This is usually a quiet, undisturbed spot but some house cats will demand more human contact.Mammary development becomes noticable in the last week of pregnancy, especially in maiden cats. Rectal temperature may fall a few days before parturition, but this is not a reliable indicator.

Stage 1

  • Restless
  • Frequently visits the site for kittening
  • Occasionally lies down and will strain unproductively.

Stage 2

  • Straining in lateral recumbency.
  • Rapid expulsion of kittens with a short interval between each birth.
  • Parturition usually complete within a few hours.
  • If the queen is alarmed, this may disrupt the pattern and she may move the kittens to a new area before parturition resumes.
  • Soon after birth the kittens begin to suckle.

Stage 3

  • Placentae usually expelled still attached to the foetus or shortly afterwards.
  • Consumed by the queen.
  • Breakdown of marginal haematoma releases biliverdin, giving the discharge a brownish colour.



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