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Gestation and Foaling


									Gestation and Foaling
Gestation Length

          • Average 338-343
          • Normal gestation
            can range from
            320-380 days.
Gestation Length
         • Gestation length shorter
           in TB and SB (325-340)
           than Draft mares (350-
         • 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
  – Fixation of the embryo
    (gestational sac)
    occurs at ~ 16 days
    post ovulation
    Equine Gestation Hormones
• 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
•   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
     – 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 takes over
  progestagen production ~d
  100 until foaling.
• Complete placental
  formation is done at 150
                              DAY 150 - Firm
                              placental attachment
  Impending Birth
Vaccinate & Deworm 30
  day prior
Most Obvious
• Hypertrophy mammary
  glands obvious from 8th
   – 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
• 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
  – End: rupture of
    chorioallantois (water
  – 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
  – 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    “Red Bag”
  min after first water breaks
• Rectovaginal perforation
• Mare foals while standing
           Stages of Parturition
• Stage 3
    – Onset: delivery of fetus
    – End: passage of the fetal
    – Expel placenta 1- 3 hrs
 •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
• 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.
                                             Placental with fetus showing
• Hippomanes are yellowish/green
  pasty concentration products of fetal      the "cervical star", site of future
  urine and contain large numbers of         rupture of membranes.
  birefringent crystals
           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
    •Length of umbilical cord &
    •Appearance of gross
    lesions, missing pieces
•   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.
• 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

                                          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.

• 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
• First milk secreted by a mare coming into
• During last 2-4 weeks of gestation
• Under hormonal influences
• Transfer of passive immunity to the suckling
  foal (“Liquid Gold”) Specificity of protection
  achieved by vaccinating pregnant mares 30-
  60 days before parturition
• Produced only once – beware of leakage!
• Provides energy to foal
• Encourages passage of meconium
• Relates directly to antibody content
• Good quality:
   ≥ 50 (70) g/L IgG and specific gravity > 1.060
   Thick, sticky, yellow secretion
• Decreased quality:
  Maiden mares and mares > 15 y of age
  Certain breeds (Standardbred)
  Shorter gestation (early foals)
  Sick mares
  Poor foaling conditions
Evaluating Colostrum Quality
• Measures specific gravity/density
  of colostrum
• Approx. 6 ml of colostrum needed
• Specific gravity >1.060 indicates
  good quality
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
Evaluating Colostrum Quality
ARS Refractometer - Results
• Average total volume: 5 liters
  (3.2-7.0 l)
   • Primiparous < multiparous
   • Decreased in stressed,
      injured or ill mares
   • Decreased in mares with
     mastitis or other damage to
Evaluating Colostrum Quality
• Assess before foal suckles
• 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
   – 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
       Mare                                          Foal IgG






        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
 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
• 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

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