Gestation and Parturition Flashcards
What is the average gestation length?
340 days
What is the range of gestation length?
320-365 days (or more)
At what point is the foal viable?
320 days
What factors affect gestation length?
-mare body condition (thin = longer)
-day length (Jan/Feb mares have longer gestation)
-health of mare/foal (health issues may cause early foaling)
-breed/type (ponies have shorter gestation)
-foal sex (gestation with colts is usually longer)
At Day 0 of gestation what occurs?
ovulation, fertilization occurs in the oviduct
At day 6ish of gestation what occurs?
conceptus leaves the oviduct
-it is mobile in the uterus
When is the conceptus detectable in the uterus (with a high powered ultrasound)?
around day 9
At day 16ish of gestation what occurs?
conceptus fixes in a uterine horn
-detectable by ultrasound
At day 23ish of gestation what occurs?
the heart beat is present
-detectable by ultrasound
At day 40 of gestation what occurs (as early as day 35)?
embryo transitions to fetus
-fetal activity and physical development (looks like a horse now)
At day 90ish of gestation what occurs?
placental development is complete
At day 240 of gestation to parturition what occurs?
most fetal mass is accumulated (in the last 3 months)
Early embryonic loss
loss of conceptus prior to 35-40 days (post ovulation)
Abortion
loss of pregnancy between 40 and 310 days (fetus is not viable between these times)
Premature delivery
weak or dead foal pre-term (usually less than 320 days)
Dystocia
a difficult delivery (a full-term dead foal is not considered an abortion)
What are the two sacs of the placenta?
-amnion
-chorioallantois (allantochorion)
Amnion
a white translucent sac of the placenta
-surrounds the fetus
-contains amniotic fluid
Chorioallantois (allantochorion)
a sac of the placenta that surrounds the amnion
-contains allantoic fluid (the “water”)
-has two sides: chorion and allantois
Chorion
the side of the chorioallantois that is attached to the uterus
Allantois
the side of the chorioallantois that is on the side towards the fetus
Umbilical cord
contains blood vessels that transport nutrients and oxygen to the fetus and takes CO2 and some other wastes away
What does the umbilical cord connected to?
the chorioallantois through several tissue layers (keeps the blood cells apart but lets the nutrients/O2 in and the CO2 out)
Do maternal and fetal blood supplies mix?
No
Urachus
connects to the fetal bladder and empties into the allantoic fluid
Where is the urachus found?
in the umbilical cord
Parturition overview:
- the foal breaks through the chorioallantois placenta, allantoic fluid (the water) spills out
- the amnion emerges
- the foal breaks the amnion then emerges
- the placenta is expelled
Pre-partum changes in mares
-loosening of tail muscles (relaxed pelvis)
-elongation of vulva
-udder development
Stage I of parturition lasts how long?
1-3 hours
What occurs during stage 1 of parturition?
-foal changes position
-uterine contractions become more apparent
-mare may be uncomfortable, paw, sweat, roll, etc.
-rupture of the chorioallantois at the end (“water breaking”)
How long does stage 2 of parturition last?
less than 40 minutes (less than 20 minutes is better)
What occurs during stage 2 of parturition?
-begins with the rupture of the chorioallantois (water breaking)
-ends with expulsion of the foal