Normal Parturition - Anatomy & Physiology

Stages of Parturition

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.

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.