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.

Ewe

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

Stage 2

• Completed within 1 hour usually.
• Lambs normally 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

Most farrowing takes place at night. The foetal membranes of adjacent piglets are usually fused and because individual or aggregated afterbirths may be expelled during the phase of foetal expulsion as well as after the birth of the last foetus there are no real separate stages of labour.

• Sows in late pregnancy usually sleep in lateral recumbency in the 24 hours before birth of the first piglet.
• Restlessness
• Bed making activity
• Intensely active period followed by recumbency and rest.
• Following this period of rest, clawing of the bedding resumes.
• Several alternating periods of rest and bed-making.
• In the hour preceeding the birth of the first piglet, the sow settles into lateral recumbency.
• Mammary growth occurs in late gestation.
  • 1-2 days before farrowing the individual glands are clearly demarcated, turgid, tense and warm.
  • Milk can be expressed during the final 24 hours.
• Progressive swelling of the vulval labia from ~4 days before parturition.
• Vulval mucosal becomes reddened
• Sows usually remain in lateral recumbency, but guilts get up after the first or second piglet and change from one side to the other, or from lateral to ventral recumbency.
• Straining and paddling leg movements.

• Births are heralded by passing of a small quantity of foetal fluid and marked by tail twitching.
• Expulsion of the first piglet requires the most effort.
• Allantochorion and amnion usually rupture as the conceptus traverses the birth canal.
  • Occasionally piglets are born within the amnion.
  • Foetus may be surrounded by membranes of another foetus.
• Offspring delivered randomy from both uterine horns.
• Average duration of the expulsive stage is 2-3 hours.
• Mean interval between successive births is 16 minutes.
• Umbillical cords may be intact or ruptured.
• Piglets are active and attempt to suckle within a few minutes.

• Foetal membranes are usually expelled as 2/3 masses of joined allontochorions with placental stalks of the umbillical cords indicating the number of conceptuses in each mass.
• Single afterbirths may also be voided.
• One or more masses are usually passes before all the piglets are born.
• Largest mass is usually passed ~4 hours after the birth of the last piglet.

• When all piglets have been expelled, the sow usually stands up and micturates.
• Then lies down again
  • Risk of crushing the piglets!
• Sow remains down for a period of time and allows the piglets to suckle.

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.