Gestation and Foaling
Gestation Length
• Average 338-343
days.
• Normal gestation
can range from
320-380 days.
Gestation Length
• Gestation length shorter
in TB and SB (325-340)
than Draft mares (350375d)
• Mares bred in late
winter & early spring
have gestation lengths
that average 10 d
longer then those born
in summer.
• Mares with fillies foal on
average 3 d earlier
Early Embryo
• 5-6 days enters uterus
• Migrates to day 16.
– Embryo migrates in the
uterus for ~ 16 days to
release a 'signal' that
pregnancy is
established.
– Fixation of the embryo
(gestational sac)
occurs at ~ 16 days
post ovulation
Equine Gestation Hormones
Progesterone/Progestogens
• Progesterone initially rises, followed by a slight ↓ then ↑ to a peak at d
80, then gradually ↓ to 1-2 ng/ml during mid-late gestation (d 150).
• Second ↑ associated with formation of accessory & secondary CL.
• The 5 α pregnanes rise from mid gestation to term.
– Produced from maternal cholesterol
• Late gestation progestagen rises (last month of pregnancy)
Equine Gestation Hormones
Estrogens
•
Mare ovarian estrogens begin to ↑ at d 38-40.
– From gonadotropin stimulation of luteal tissue
– Late in gestation maternal estrogen production ↑.
•
D 70-80 a 2nd ↑ of estrogens from the fetal-placental unit occurs.
– Secreted by fetal gonads.
•
•
Fetal estrogens peak at about 210 d & decline & are basal
Estrogens appear in the mare's urine in large amounts in the latter half of
gestation.
– Estrone sulfate: Can be measured with a kit. Derived from the placenta, it is an
indicator of fetal viability. It declines within a few days of fetal death.
Equine Gestation Hormones
Equine Chorionic Gonadotropin (eCG)
• 36-38 days - fetal tissue along the chorionic girdle begin to invade
the endometrium & form the endometrial cups.
• Endometrial cups - eCG-Equine Chorionic Gonadotropin
• Produced ~ d 37-42,
• Peak - d 60-80
• Endometrial cups start to decline, disappearing around d 120-150.
• Causes luteinization of follicular waves to create secondary CLs.
• Has an FSH-like action in many other species, it has LH-like activity
in mares.
Placenta
• Placenta takes over
progestagen production ~d
100 until foaling.
• Complete placental
formation is done at 150
days.
DAY 150 - Firm
placental attachment
Impending Birth
Vaccinate & Deworm 30
day prior
Most Obvious
• Hypertrophy mammary
glands obvious from 8th
month
– Maiden may display little
until just before foaling
• Distention of the teats
4-6 d pre-foaling
• Waxing of the teats
1-72 hrs pre-foaling
• An increase in milk Ca
1-3 d pre-foaling
Impending Birth
More Subtle Signs
• Softening and flattening
of the muscles in the
croup
• Vulva becomes relaxed
& elongated. Maximal
hours before parturition
• Visible changes in the
position of the foal
• Vulva – thick & puffy with
edema and may elongate
Stages of Parturition
• Stage 1
– Onset: initial uterine
contractions
– End: rupture of
chorioallantois (water
bag)
– 1-2 hr
– Mare may stand up, lie
down, roll, pace, look
or bite at flanks,
sweat, urinate
Stages of Parturition
• Stage 2
– Onset: rupture of
chorioallantois
– End: delivery of fetus
– Timeline 30 min
– Contractions occur in
groups of 3-4 followed
by a rest period of 3 to
5 minutes
• When the chest is
through the vulva
the foal can
breathe on its own.
May go in &
remove the
amniotic sac.
• Not breathing – rub
foal, take straw and
put in nose, breath
into nose
Foaling Emergencies
May Need Assistance
• Red mass evident at vulva
(placenta seperation)
• Strong straining & no feet
evident at vulva within 5 min
• Heavy straining with feet in
vulva but no further progress
in 10 min
• One foot missing
• No progress for more than 15
min after first water breaks
• Rectovaginal perforation
occurs
• Mare foals while standing
“Red Bag”
Stages of Parturition
• Stage 3
– Onset: delivery of fetus
– End: passage of the fetal
membranes
– Expel placenta 1- 3 hrs
post-foaling
•Examine Placenta
Fetal Membranes at Parturition
• Allantochorion - Fusion of the allantois with the chorion results in the
allatochorion. At term ~2/3 of placental weight.
– Chorionic (villous) surface is intimately applied to the maternal
endometrium and is responsible for the formation of
microcotyledonary attachments. Grossly, it appears as a red
velvet surface
• Allantoamnion - allantois surrounds the amnion by the 4th week of
gestation, forming the allantoamnion.
– At term, this membrane is white and opaque, with large blood
vessels coursing over the inner surface.
– 1/3 of weight at term
Fetus @ 3 months
Fetal Membranes at Parturition
• Umbilical cord - Results from the expansion of
the amnion & allantois around the remnants of
the yolk sac & vitelline duct
– Anchors the fetus to the original implantation site at the
base of the gravid horn on the dorsal wall of the uterus.
– Cord length is directly correlated with the weight of the
allantoamnion and the allantochorion.
Important Features of the Equine
Placenta
• Cervical star visible as a region
without the red villi and has radiating,
bare, white areas from its center
• Allantochorionic Pouches Maternal rejection of the endometrial
cups results in their sloughing into
adjacent invaginations of the
overlying allantochorion. These
appear as pedunculated structures
forming a ring around the site of
umbilical cord attachment at the
dorsal wall of the pregnant horn.
• Hippomanes are yellowish/green
pasty concentration products of fetal
urine and contain large numbers of
birefringent crystals
Placental with fetus showing
the "cervical star", site of future
rupture of membranes.
Placenta Examination
•Arrange the membranes in a
capital "F" position, with the
pregnant horn uppermost and the
body forming the vertical bar of
the "F"
•Tip of the nonpregnant horn is
the most likely part of the
placenta to be retained
•Placenta Examination
•Weight
•Length of umbilical cord &
location
•Appearance of gross
lesions, missing pieces
Allantochorion
•
•
•
Usually expelled with the allantoic surface outermost
Examine both chorionic and allantoic surfaces.
Color
– Rich red or maroon color with the gross appearance of a velvet-like surface.
– Pale or fibrotic areas indicate sites of placental detachment or lack of
microcotyledon formation
– Nonpregnant horn is generally paler than the rest of the chorion.
•
Thickness
– Compared with the pregnant horn, the non-pregnant horn is thinner in section,
puckered, and smaller in size.
Allantochorion
• Body Pregnancy
– Although usually resident in one uterine horn with extension into the
body of the uterus, the occasional fetus will develop largely within the
body of the uterus. The characteristic placental finding is short,
symmetrical placental horns
• Exudate
– Presence may be considered as presumptive evidence of microbial
intrauterine infection
Allantochorion
Chronic Inflammation
Cervical Star
• Cervical Star Thickening
– majority of Intrauterine infections ascend through an
incompetent cervix.
– Gross thickening, exudate, and a line of demarcation
between this area and the adjacent placental body are
characteristic findings of placentitis
• Allantoamnion
– assessed for uniform thickness and color
– smooth, white, opaque, uniformly thin membrane.
Allantochorion
• Umbilical Cord
– Assessment of length, degree of twisting, and the
presence of any vascular compromise
– Abnormal findings include cord seperation, excessive
rotation, kinking, aneurysms, intramural hematomas,
thrombosis, edema
– 95% of normal equine pregnancies, the umbilical cord
measures between 36 and 83 cm, with an average
length of 55 cm
Postpartum Mare & Foal Care
Umbilical Cord Care
• Allow foal to break fetal membranes.
• Never cut the cord.
• Spray umbilical cord stump with antiseptic
solution 3-4X per day for 3-4 days
Ascending placentitis
Premature seperation
Retained Placenta: Treatment
•
•
•
•
•
•
•
After 2 hrs
Oxytocin
Infusion of fluid into allantoic cavity
Antibiotics
Non-sterioidal anti-inflammatory drugs
Frog support pads
Deeply bedded stall
Colostrum
• First milk secreted by a mare coming into
lactation
Production
• During last 2-4 weeks of gestation
• Under hormonal influences
Importance
• Transfer of passive immunity to the suckling
foal (“Liquid Gold”) Specificity of protection
achieved by vaccinating pregnant mares 3060 days before parturition
• Produced only once – beware of leakage!
• Provides energy to foal
• Encourages passage of meconium
Colostrum
Quality
• Relates directly to antibody content
• Good quality:
 ≥ 50 (70) g/L IgG and specific gravity > 1.060
 Thick, sticky, yellow secretion
Colostrum
Quality
• Decreased quality:
Maiden mares and mares > 15 y of age
Certain breeds (Standardbred)
Shorter gestation (early foals)
Sick mares
Poor foaling conditions
Colostrum
Evaluating Colostrum Quality
Colostrometer
• Measures specific gravity/density
of colostrum
• Approx. 6 ml of colostrum needed
• Specific gravity >1.060 indicates
good quality
Colostrum
Evaluating Colostrum Quality
ARS Refractometer
• Designed for measurement of
sugar concentration of
solutions (BRIX type)
• 1-2 drops of colostrum needed
• Results in less than 1 minute
http://www.arssales.com/equine/html/refractometer.html
Colostrum
Evaluating Colostrum Quality
ARS Refractometer - Results
Colostrum
Volume
• Average total volume: 5 liters
(3.2-7.0 l)
• Primiparous < multiparous
mares
• Decreased in stressed,
injured or ill mares
• Decreased in mares with
mastitis or other damage to
udder
Colostrum
Evaluating Colostrum Quality
When?
• Assess before foal suckles
How?
• Physical appearance
 Thick, sticky, yellow secretion indicates good quality
 Dilute, white or translucent secretion indicates poor quality
 Stall Side Tests
Banking of Colostrum
•
Only good quality colostrum
•
Storage at -20ºC:
– IgG concentration stable for 12 months
– Other immune components (complement, etc) and
nutritional components decrease significantly
•
Storage at -70ºC:
– Permanent maintenance of all components
Passive Transfer
• Successful passive transfer depends on precise sequence of
events
– Antibodies must be present in colostrum
– GI tract must absorb the large proteins whole- “pinocytosis”
• Foal must receive within 1st 8-12 hrs of life
• Requires 8-12 hours for antibodies to show up in the blood
• Uptake declines to almost zero by 12-24 hours
Antibody levels in Foal
1200
Mare
IgG
Foal IgG
1000
800
600
400
200
0
1
2
3
4
5
6
7
8
9 10 11 12
wk wk wk wk wk wk wk wk wk wk wk wk
•Foal produced antibodies first appear in blood stream at about 3
weeks of age
•Normal adult levels of foal produced antibodies by 4-5 months
Foal Immune Status
What are safe levels of IgG in the foal?
• True safe levels not known
• Goal: serum IgG > 800 mg/dl
• If < 800 mg/dl = Failure of
Passive Transfer (FPT) - As high as 20% of all foals
 Marginal FPT: IgG 400-800 mg/dl
 Partial FPT: IgG 200-400 mg/dl
 Complete FPT: IgG < 200 mg/dl
Foal Immune Status
Evaluation of serum IgG status
When?
 Typically at 12-24 h after birth
 Peak serum levels of IgG achieved by 18h
 Absorption of immunoglobulins from small intestine
essentially complete
 If failure of passive transfer: treat with IV plasma
 Can measure early at 6-12 h
 IgG first detected in foal’s serum at 6 h of age
 If no IgG or very low level at 6-12 h: can give colostrum to
increase levels
Foal Immune Status
Evaluation of serum IgG status
Snap Foal IgG Test
• ELISA
• Use whole blood, serum, or plasma
• Calibrator spots indicate IgG
levels of 400 and 800 mg/dl
• Sample color is proportional to
IgG content
• Results in 10-15 min.
• Expensive but convenient