Parturition

Question 1

What are 5 morphological changes we see with impending parturition?

Answer 1

1. Abdominal enlargement
2. Mammary gland enlargement- w/ milk secretion several days before birth
3. Oedema of ventral abdomen, udder and beneath vulva
4. Vulva swells and may discharge muscous
5. Relaxation of pelvic ligaments

Question 2

What causes this oedema we see in impending parturition?

Answer 2

Mostly a problem with venous return. There’s a massive space occupying lesion in the abdomen which is causing compression of some blood vessels. At this point they are also not moving around very much, and this restricted movement can also contribute to this.

Question 3

What are 4 behavioural changes we see with impending parturition?

Answer 3

1. Cows will start to avoid aggressive behaviour to protect foetus 6 weeks prior (this may also be due to the fact that they’re finding it harder to move around themselves)
2. Eventually, they will avoid social interaction altogether
3. Increased restlessness
4. “Nesting instinct” especially in pigs, and cats and dogs

Question 4

What are the three stages of parturition?

Answer 4

Stage 1- Initiation of myometrial contractions (removal of P4 block)
Stage 2- Expulsion of foetus
Stage 3- Expulsion of foetal membranes

Question 5

What initiates stage 1?

Answer 5

Foetal stress

Question 6

What is the basic pathway from fetal stress to contractions?

Answer 6

1. Fetus outgrows both uterine space and placenta’s ability to provide O2 and nutrients
2. Fetus becomes stressed
3. > fetal ACTH
4. > fetal cortisol
5. Activation of 3x sex steroid enzymes that convert P4 to E2
6. Removal of P4 block allows myometrial contractions

Question 7

What effect does the increase of E2 relative to the decreasing P4 have on the dam?

Answer 7

Increased E2 levels lead to hydration of collagen, which causes relaxation of ligaments, and also increased oedema which helps to lubricate the repro tract.

Question 8

What produces PGF2alpha?

Answer 8

The placenta )mainly maternal endometrium)

Question 9

What is the function of PGF2alpha release?

Answer 9

It can assist to remove the P4 block, by causing luteolysis and regression of the CL maintaining the pregnancy.

Question 10

What facilitates the release of PGF2alpha?

Answer 10

Increased levels of fetal cortisol

Question 11

What type of molecule is relaxin?

Answer 11

A glycoprotein

Question 12

What produces relaxin?

Answer 12

Uterus or CL depending on the species

Question 13

What stimulates relaxin synthesis?

Answer 13

PGF2alpha

Question 14

Relaxin prepares the dam for parturition. How?

Answer 14

• Causes softening of CT in the cervix
• Causes relaxation of pelvic ligaments

Question 15

What is the function of E2 in non pregnant animals?

Answer 15

It causes contractions that get rid of debris and dead sperm cells post breeding. It has similar effect in the pregnant animals, promoting myometrial contractions to expel the fetus.

Question 16

What is Ferguson’s reflex?

Answer 16

This refers to the pressure on the cervix by the fetus causes a positive feedback loop leading to increased secretion of oxytocin. The pressure on the cervix stimulates sensory neurons. These afferent neurons travel through spinal cord up to where the neural pathway terminates at the paraventricular nucleus (PVN). Oxytocin is then released from the posterior pituitary. Oxytocin then stimulates contraction of the myometrium, and we will also see abdominal contractions.

Question 17

What signals the technical start to stage 2 of parturition?

Answer 17

The rupture of the chorio-allantois

Question 18

The rupture of the chorioallantois in stage 2 causes what?

Answer 18

The release of fluid which helps lubricate the cervix and vagina.

Question 19

Stage 2 needs two types of strong contractions, what are they?

Answer 19

Myometrial and abdominal contractions

Question 20

What happens to the fetus as it enters the cervix?

Answer 20

It becomes hypoxic

Question 21

What is the difference in colour/texture between allantoic and amniotic fluid?

Answer 21

Allantoic fluid comes from the fetus’s urinary waste and as such is a yellow colour. Amniotic fluid is more slippery, more viscous, more like a lubricant, and is derived from the fetus’s respiratory waste.

Question 22

The increased movement of the fetus helps to facilitate what?

Answer 22

Myometrial contractions

Question 23

What effect does increased myometrial contractions have on the level of oxytocin produced?

Answer 23

+ve feedback loop! = Ferguson’s reflex
cause > myometrial contractions lead to > pressure on the cervix

Question 24

What is dystocia?

Answer 24

A difficult birth/prolonged stage 2

Question 25

What are three big causes of dystocia?

Answer 25

1. Excessive size of fetuses- = fetomaternal disproportion-> common in some cattle and dog breeds
2. Improper fetal rotation- abnormal positioning. Happens in 5% of cattle births
3. Multiple births- can be because two are presenting at the same time, 1 is positioned abnormally and blocking the passage of the 2nd, or because of uterine inertia due to fatigue or sustained contractions.

Question 26

When does the expulsion of fetal membranes usually occur?

Answer 26

Immediately following expulsion of the fetus. Sometimes part of the amnion will come w the fetus, or break away with the fetus

Question 27

What needs to occur to allow the chorionic villi to become detached from crypts of the maternal side of the placenta?

Answer 27

For this to occur we need vasoconstriction of the arteries both in the villi and on the maternal side. This almost always happens reliably on the fetal side- when it doesn’t happen on the maternal side is when we run into problems with RFMs.

Question 28

Any time there’s an interruption to the normal parutrition, RFMs are a risk. What are 4 examples of disruptions to normal parturition?

Answer 28

1. C-sections
2. Dystocia
3. Red bag deliveries (premature placental separation)
4. Abortion

Question 29

To release the membranes, what needs to happen to each individual placentome?

Answer 29

Each discrete cotyledon and caruncle need to separate individually

Question 30

What are two ways RFMs can occur? (in regards to improper separation of individual cotyledons/caruncles)

Answer 30

• Lack of cotyledon proteolysis (collagenolysis)
• Lack of enzymological degradation of the anchoring systems