Lesson 73 - Pregnancy, Partition, Dystocia

What is a zygote?

single cell formed by the fertilization of an oocyte by a spermatozoon

What happens to a zygote as it travels through the oviduct?

undergoes mitotic divisions

What is an embryo?

early development stage following the zygote

How long is the embryonic period in cattle?

up to approximately day 42 of gestation

What is conceptus?

entire product of conception at any point between fertilization and birth

What is the fetus?

stage of prenatal development following the embryonic period, characterized by the presence of all major body organs

When does fetal stage begin in cattle?

after day 42 of gestation

What is eutocia?

normal birth

What initiates parturition in cattle?

1. maturation of fetal hypothalamus/pituitary

2. increase ACTH

3. increased fetal cortisol

What does increase fetal cortisol in cattle cause?

1. increase in COX2 leading to increase in PGF2alpha in the trophoblast

2. increase in estrogens in trophoblast

What does increase in PGF2 alpha in the trophoblast during parturition in cattle cause?

1. luteolysis

2. activation of myometrium

What does increase in estrogens from the trophoblast during cattle parturition cause?

activation of myometrium

What causes cervical dilation in cattle during parturition?

decline in progesterone in maternal blood

When is the preparatory phase in cattle?

2-3 weeks prior to parturition

What occurs during the preparatory phase in cattle?

1. rapid fetal growth

2. enlargement of udder/bagging up

3. production of colostrum

4. increased estrogen levels

What does increase estrogen levels during the cattle preparatory phase cause?

1. vulva becomes enlarged and soft

2. vaginal mucus more copious

3. relaxation of pelvic ligaments

4. gluteal muscles sink

5. tail head becomes more elevated

What occurs a few hours before cattle parturition?

1. vulva becomes edematous

2. cervical mucus plug liquefies

What is the first stage of parturition?

1. cervical dilation

2. expulsion of the fetus

3. expulsion of the fetal membranes

What are the steps of cervical dilation?

1. passive

2. active

What happens with passive dilation of the cervix?

1. caused by decreased cervical tone from estrogen

2. external os opens first creating a funnel shape

What is the duration of the first phase in multiparous cows?

2-4 hours

What is the duration of the first phase in primiparous cows?

4-6 hours

What triggers active dilation in the cow?

strong myometrial contractions

What happens when the fetal membranes and parts enter the cervix during active dilation in cows?

expand the cervix further stimulating oxytocin release which reinforces contractions

What is the fergusons reflex?

enhanced uterine contractions in response to cervical stretching which causes oxytocin release

A cow is showing signs of abdominal discomfort, restless, isolates herself, and intermittently arches her back and turns her head towards her flank. What phase is she in?

first stage with active cervical dilation

What phase of cervical dilation is not accompanied by behavioral changes?

passive

What marks the end of the first stage of parturition in cows?

rupture of chorioallantois

What contractions are seen with the second stage of parturition in cows?

strong abdominal contractions with arching of the back, extension of the tail, and tensing of the abdominal musculature

What signs are seen with second stage of parturition in cows?

1. strong abdominal contractions

2. alternates between standing and recumbency

3. may vocalize

4. amnion appears and ruptures

What is the average length of the second stage of parturition in cows?

2-4 hours but longer in heifers

What causes the detachment of the fetal membranes from the uterus in cows?

1. decrease in blood flow due to umbilical cord rupture causes cotyledon shrinkage

2. uterine contractions aid

How long is the third stage of parturition in cows?

about 8 hours on average (minutes to 12 hours)

What features match with ruminant natural mating?

1. copulation is 1-3 seconds

2. small volume, very concentrated

3. deposits at external os of cervix

What features match with stallion natural mating?

1. copulation is 20-60 seconds

2. large volume, not very concentrated

3. deposits at external os but forced into uterus under high pressure

What features match with boar natural mating?

1. copulation is 5-20 minutes

2. large volume, not very concentrated

3. deposits at cervix and uterus

What features match with dogs natural mating?

1. copulation is 5-20 minutes

2. moderate volume, not very concentrated

3. deposits at fornix vagina

What must the sperm be able to do for successful fertilization?

1. traverse the cervix, uterus, tubes

2. undergo capacitation

3. bind to oocyte

4. undergo acrosome reaction

5. penetrate the zona pellucida

6. fuse with oocyte membrane and enter cytoplasm

What happens when the sperm makes contact with the egg?

acrosome reacts with zona pellucida releasing hydrolytic enzymes

What happens once the sperm makes it through the zona pellucida?

plasma membrane of egg and sperm fuse and sperm nucleus enters the egg

How does the egg ensure that another sperm doesn't fertilize it after it has been fertilized?

cortical granules fuse with egg plasma membrane making the vitelline layer impenetrable to sperm

What is capacitation?

surface molecules are removed exposing portions of the molecules that bind to the zona pellucida

How does the sperm motility change when in the uterine tube?

they become hypermotile

Where does capacitation occur?

female reproduction tract

What happens during the acrosome reaction?

binding to the ZP causes fusion of the spermatozoal plasma membrane and outer acrosomal membrane which exposes enzymatic vesicles

What stage does the embryo reach the uterus?

morula

When does the embryo reach the uterus?

4-5 days after ovulation

What occurs around day 7 after ovulation?

morula becomes blastocyst

Which animal has faster embryonic processes?

sows

What is a critical time for the embryo?

hatching phase

What is an important hormone for maternal recognition of pregnancy in cows?

interferon tau

What secretes IFN-tau in cows for MRP?

embryo

What is the function of IFN-tau in cows MRP?

1. bind to endometrial cells and inhibit oxytocin receptor synthesis

2. promotes production of proteins crucial for embryo survival from endometrial glands

Where does oxytocin come from in cows?

corpus luteum

When does MRP happen in cows?

day 16-17 after ovulation

What must occur for a pregnancy to be viable in sows?

minimum of four embryos must be present in the uterus at the time of MRP

What is the main mechanism in cows to prevent luteolysis during pregnancy?

IFN-tau from embryo inibiting oxytocin receptor synthesis

What is the main mechanism in sows to prevent luteolysis during pregnancy?

embryos produce estradiol that causes PGF 2 alpha to be rerouted into the uterine lumen where is it destroyed

How long is a cows pregnancy?

280 days

How long is a horses pregnancy?

340 days

How long is a sheeps pregnancy?

147 days

How long is a goats pregnancy?

150 days

How long is a pigs pregnancy?

114 days

What does it mean if there are more layers between maternal and fetal blood?

less antibodies and nutrients can diffuse across

What placentation do pigs have?

diffuse epithelial-chorial

What is epithelial-chorial placentation?

all 6 layers present

What are the placentation layers?

1. maternal endothelium

2. maternal connective tissue

3. material epithelium

4. fetal epithelium

5. fetal connective tissue

6. fetal endothelium

What is syndesmo-chorial placentation?

missing maternal epithelium

What is endothelial-chorial?

missing maternal epithelium and connective tissue

What is hemo-chorial?

missing all three maternal layers

What is hemo-endothelial?

only has fetal endothelium layer

What placentation do horses have?

diffuse epithelial-chorial

What placentation do ruminants have?

cotyledonary epithelial-chorial or syndesmo-chorial

What placentation do dogs and cats have?

zonary endothelial-chorial

What placentation do rats and rabbits have?

hemo-endothelial

How many placentomes do cows have?

80 - 120

What type of placentomes are there?

1. convex in cow

2. concave in sheep, goat

What is the outer layer of the fetal membranes?

chorio-allantoic

What is the inner layer of the fetal membranes?

amniotic

Where does fertilization occur in mares?

oviduct

What happens to the embryo once it is fertilized in mares?

remains in oviduct for about 6 days

What is the mechanism for equine MRP?

embryo remains round and mobile and must come into contact with all parts of endometrium to prevent PGF2 alpha production

What does the embryo develop in early equine pregnancy?

tough glycoprotein capsule after entry into uterus

When does the equine embryo lose its capsule?

day 22

How long is the equine embryo mobile?

til day 16 after ovulation

What does the equine embryo secrete?

prostaglandins especially PGE2

What occurs at day 16 in equine pregnancy?

1. fixation of embryo

2. increase uterine tone

3. embryo diameter changes

4. embryo capsule becomes sticky

Where does fixation occur in horses?

base of a uterine horn and does not need to be on the side of ovulation

How long is the primary CL initially present in equine?

up to day 35

How long are the resurged primary CL and secondary CLs present in equine?

up to about day 150

What happens at about day 120 in equine?

feto-placental unit takes over by secreting 5-alpha pregnanes

When do endometrial cups begin forming in horses?

from day 35

What are endometrial cups?

trophoblastic cells of fetal origin that burrow into endometrium of the mare

What do endometrial cups in horses secrete?

eCG also known as PMSG

What is the function of eCG?

1. resurgence of primary CL

2. development of secondary CLs

When do endometrial cups disappear?

day 120 even if fetus dies

What occurs during day 150 through 220 in equine pregnancy?

fetal gonads are bigger than mares gonads

What are the fetal gonads during day 150-220?

1. pump out dihydroepiandrosterone (DHEA)

2. produces progestagens like 5 alpha pregnanes

What is the function of the equine fetal dihydroepiandrosterone?

converted by the placenta to various estrogens used for pregnancy diagnosis and assessment of fetal viability

What is the main source of progestagens during mid-gestation in the mare?

fetus