AVS 466 Horse Science and Management

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AVS 466 Horse Science and Management

• Dirk K. Vanderwall
• April 21, 2008
• Early Pregnancy in the Mare

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Terminology

• Embryo
• Inner-cell mass
• Embryonic disk
• Embryo-proper
• Embryonic vesicle
• Conceptus
• Fetus

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Early Embryonic Development(before
ultrasonographic detection)

• Oviduct
• Cleavage stage (2 cell, 4 cell, etc.)
• Morula
• Uterus
• Compact morula
• Early blastocyst
• Blastocyst
• Inner cell mass
• Expanded blastocyst

Ginther, 1992
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Day 7 embryo
Day 11 embryo
Ginther, 1992
inner cell mass
embryonic disk
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Ultrasonographic MorphologyDay 10 to 15
Ginther, 1995
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Day 13 Conceptus
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Embryo Mobility

• Occurs up to Day 16
• Fixation occurs on Day 16 at the base
  of one uterine horn
• Independent of the side of ovulation
• Period of maximum mobility is Day 11 to
  14
• Uterine contractions are the propulsive
  force
• Necessary for maternal recognition of
  pregnancy

Ginther, 1995
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Embryo Mobility
PGF2a
PGF2a
Ginther, 1992
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Embryo Fixation(occurs on Day 16)
Ginther, 1995
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Ultrasonographic MorphologyDay 16 to 45
Ginther, 1995
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Day 32 Conceptus
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Growth of the Conceptus
Ginther, 1995
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Twins

• Dizygotic
• Multiple ovulation
• Unilateral vs. bilateral
• Synchronous vs. asynchronous

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Twins
Synchronous
Asynchronous
Ginther, 1995
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The problem with twins
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Surviving Twins
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Fixation of Twins
Ginther, 1995
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Spontaneous Outcome of Unilaterally Fixed
Twins(Deprivation Hypothesis)
Ginther, 1995
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Diagnosis of Twins

• If possible, examine, and look for twins
  in, all mares on Day 14 after ovulation,
  regardless of the number of detected
  ovulations
• Document findings in reproductive record
• Presence of two embryonic vesicles
• Differentiate from a cyst(s)
• Twins in contact may be difficult to
  discern
• Large, oblong vesicle
• Membrane of apposed vesicles
• If necessary, recheck mare to see if
  vesicles separate

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Twin Management

• Intrinsic factors
• Mobility phase
• Post mobility phase
• unilateral vs. bilateral
• Pre or post endometrial cup formation
• Extrinsic factors
• Stage of breeding season
• Early vs. late

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Twin ManagementMobility Phase

• Manual reduction (elimination) of one
  conceptus
• If twins are initially in contact, wait
  for them to separate, and then manually
  reduce one conceptus

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Twin ManagementPost - Mobility Phase
Bilateral Twins

• Manual reduction of one conceptus
• The earlier, the better

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Twin ManagementPost - Mobility Phase
Unilateral Twins

• Wait to see if natural reduction occurs
• Reduce both twins and breed again
• Early in breeding season
• Transvaginal needle-guided reduction of one
  conceptus

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Manual Twin Reduction

• Generally pinch smaller twin if different,
  or the twin that doesnt look right
• Prophylactic treatment ?
• NSAIDs
• Progesterone

Ginther, 1995
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Early Pregnancy Loss

• Incidence
• 10 to 15 between Days 14 and 60 of
  gestation
• gt 25 for aged mares (gt 18 years)
• Causes
• Intrinsic
• Extrinsic

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Intrinsic Factors

• Uterine disease
• Fibrosis, endometritis
• Progesterone deficiency
• Lactation
• Foal-heat breeding
• Post-ovulation insemination
• Maternal age

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Maternal Age
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Extrinsic Factors

• Stress
• Nutrition
• Season / climate
• Sire effects
• Transrectal palpation
• Ultrasonography

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Ultrasonographic Characteristics of Pregnancy
Loss

• Irregular shape of vesicle
• Prolonged mobility
• Undersized vesicle
• Loss of heartbeat
• Dislodgement of the vesicle with loss of
  fluid
• Excessive edema of the endometrial folds
• Lack of development of the embryo-proper

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