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:

• Cervical Softening
• Coordinated Myometrial Contraction
• Voluntary contraction of abdominal muscles

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.

Cat

Stage 3

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