Puerperium - Anatomy & Physiology

Introduction

Immediately following parturition, the female enters a period of reproductive repair called the puerperium and begins lactation. For a period of time these two processes overlap.
During the puerperium uterine involution and return to ovarian function occurs.
- Involution is the reduction in size and remodelling of the endometrium so that the uterus can initiate and sustain another pregnancy.
The time required for complete uterine involution and ovarian activity to resume varies among species.
In many polyoestrous animals, the shortest possible puerperium is desirable because eligibility for a subsequent pregnancy is of high economic importance.

Myometrial Contraction and Expulsion of Lochia

Myometrium undergoes strong, repeated contractions.
The purpose of these contractions is:
- Facilitate discharge of fluids and tissue debris from the uterus.
- Compress the uterine vasculature and help minimize possibility of haemorrhage.
- Reduce the overall size of the uterus.

In most species, frequent post-partum suckling occurs and oxytocin is secreted.
In suckled animals, uterine contractions occur on a frequent basis.
- In dairy cows, the calf is usually removed 24 hours after parturition and milking takes place only 2-3 times a day.
  - Oxytocin episodes are reduced.
  - Myometrial contractions not as frequent
  - Delayed uterine involution
  - Delayed uterine involution limits fertility.

Reduction in Uterine Volume

Immediately after parturition, the uterus undergoes rapid but highly coordinated atrophy.
Uterine mass rapidly reduced to non-pregnant size.
All species: marked size reduction in the first several days after parturition.
Most species: myometrial contractions occur in 3-4 minute intervals for the first several postpartum days.
Strong myometrial contractions subside within several days.

Lochia

Shortly after parturition, a discharge called lochia is expelled from the vulva.
- Lochia is a blood- tinged fluid containing remnants of the foetal placenta and endometrial tissue.
Lochial discharge is normal in all species.
- In dairy cows, lochial discharge occurs at day 2-9 postpartum.
  - Increase in blood and tissue debris in the lochia is normal, occurs day 5-10.
    - Due to sloughing of caruncular surfaces that leaves vascular 'stubs' that leak blood.
Reduction of lochia in the uterus with myometrial contractions occuring for the first 7-10 days.
- In dairy cows, up to 2000ml is expelled from the uterus in the first 2-3 days after parturition.
  - By 14-18 days, locial discharge is almost non-existent in most cows.

Endometrial Repair

Vasoconstriction

After separation of foetal cotyledons from maternal caruncles (within 8-12 hours of delivery of the neonate) vasoconstriction occurs at the base of the maternal caruncle.

Necrosis

Irreversible cell death that leads to sloughing of the caruncular mass leaving necrotic tissue in the lochial fluid inside the uterus.
Some blood is released from the caruncular stalk generating a blood-tinged fluid.

Sloughing

About 5 days after parturition.
Caruncles lose cellular organization and integrity.
Chunks of the caruncles detach from the surface.
Remnants of blood vessels exposed on the surface.

Repair

After the decidual tissue of the caruncle has sloughed into the uterine lumen, the caruncle begins to undergo repair.
Eventually covered again with endometrial epithelium.

At the same time caruncular repair is taking place, the intercaruncular endometrial surfaces undergo repair.
Epithelium of the intercaruncular area repairs at a faster rate than the caruncles.
- Repair of intercaruncular endometrium is usually complete by day 8 post-partum.

Delay in caruncular repair compared to intercaruncular epithelium is because a large mass of caruncular tissue must undergo necrosis and sloughing before surface epithelial repair can take place.

Species Differences

Once again, the most significant example is in the dairy cow. This is the example shown above. However, there are significant species differences.

Time Required for Uterine Involution and Resumption of Ovarian Activity in Various Species

Species	Alpaca	Beef Cow	Bitch	Camel	Dairy Cow	Ewe	Llama	Mare	Queen	Sow
Time Required for Complete Uterine Involution (days)	20	30	90	30-50	45-50	30	20	21-28	30	28-30
Time Required for Resumption of Ovarian Activity	5-10 days	50-60 days (inhibited by lactation)	150 days (long natural postpartum anoestrus)	25-40 days or up to 1 year (inhibited by lactation)	18-25 days	180 days (short day breeder)	5-10 days	5-12 days	30 days	7 days (inhibited by lactation)

Elimination of Bacterial Contamination of the Reproductive Tract

Generally, parturition in domestic animals occurs in a non-sterile environment. As a result, bacterial contamination of the reproductive tract, especially the uterus, is an inevitable sequela to parturition.

The postpartum tract containing lochia is an ideal environment for the growth of bacteria.
Even though myometrial contractions remove the large volume of lochia, bacterial growth can continue.
Bacterial contamination is not always associated with pathology.
Normal post-partum events eliminate the bacterial flora within a reasonable time.
Elevated oestrodiol promotes leukosis in the uterus and elsewhere in the tract.

In some cases, high numbers of bacteria can overwhelm the natural defence mechanisms, resulting in postpartum uterine infection.
Conditions that predispose the uterus to infection are:
- Retained foetal membranes
- Dystocia
- Delay in lochial expulsion due to weak myometrial contractions.

Factors Influencing the Puerperium

Uterine Involution

Age

More rapid in primiparia than pleuriparia

Season

More rapid in spring and summer months.

Suckling vs Milking

Results are contradictory
May be a breed influence on the time taken to return to ovarian cyclicity

Climate

Heat stress can accelerate and inhibit the speed of involution.

Periparturient Abnormalities

Dystocia, retained placenta, hypocalcaemia, ketosis, twin calves and metritis delay involution.
Periparturient problems cause a delay of the process of involution by ~5-8 days.

Delayed Return to Ovarian Cyclicity

Inhibits involution

Restoration of the Endometrium

Retained foetal membranes and metritis inhibit healing.
Return to ovarian cyclicity may have an influence.

Return to Ovarian Cyclicity

This can be affected by; periparturient abnormalities, milk yield, nutrition, breed, parity, season, climate and suckling intensity and milking frequency.