Gestation and Foaling

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Gestation and Foaling
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Gestation Length

• Average 338-343 days.
• Normal gestation can range from 320-380 days.

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Gestation Length

• Gestation length shorter in TB and SB (325-340)
  than Draft mares (350-375d)
• 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

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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

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Equine Gestation HormonesProgesterone/Progestogen
s

• 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 a pregnanes rise from mid gestation to
  term. 
• Produced from maternal cholesterol
• Late gestation progestagen rises (last month of
  pregnancy)

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Equine Gestation HormonesEstrogens

• 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.

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Equine Gestation HormonesEquine 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.

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Placenta

• Placenta takes over progestagen production d 100
  until foaling.
• Complete placental formation is done at 150 days.
  

DAY 150 - Firm placental attachment
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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

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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

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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

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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

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• 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

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Foaling EmergenciesMay 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
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Stages of Parturition

• Stage 3
• Onset delivery of fetus
• End passage of the fetal membranes
• Expel placenta 1- 3 hrs post-foaling

• Examine Placenta

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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 _at_ 3 months
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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.

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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.
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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

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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.

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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

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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.

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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

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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

Premature seperation
Ascending placentitis
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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

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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 30-60 days
  before parturition
• Produced only once beware of leakage!
• Provides energy to foal
• Encourages passage of meconium

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Colostrum

• Quality
• Relates directly to antibody content
• Good quality
• 50 (70) g/L IgG and specific gravity gt 1.060
• Thick, sticky, yellow secretion

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Colostrum

• Quality
• Decreased quality
• Maiden mares and mares gt 15 y of age
• Certain breeds (Standardbred)
• Shorter gestation (early foals)
• Sick mares
• Poor foaling conditions

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Colostrum

• Evaluating Colostrum Quality
• Colostrometer
• Measures specific gravity/density
• of colostrum
• Approx. 6 ml of colostrum needed
• Specific gravity gt1.060 indicates good quality

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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

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Colostrum
Evaluating Colostrum Quality
ARS Refractometer - Results
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Colostrum

• Volume
• Average total volume 5 liters (3.2-7.0 l)
• Primiparous lt multiparous mares
• Decreased in stressed, injured or ill mares
• Decreased in mares with mastitis or other damage
  to udder

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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

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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

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Antibody levels in Foal
Mare IgG
Foal IgG

• 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

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Foal Immune Status

• What are safe levels of IgG in the foal?
• True safe levels not known
• Goal serum IgG gt 800 mg/dl
• If lt 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 lt 200 mg/dl

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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 foals serum at 6 h of age
• If no IgG or very low level at 6-12 h can give
  colostrum to increase levels

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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