Embryo Migration

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Embryo Migration
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Zygote
2-celled zygote
4-celled embryo
Morula
Blastocyst
8-celled embryo
Hatching blastocyst
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Spherical blastocysts, day 9 post mating Long,
et.al., 1992,Vet. Pathol 2960-67
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Elongated blastocysts, day 11 post mating Long,
et.al., 1992,Vet. Pathol 2960-67
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Embryo Migration

• Fertilized ovum begins to migrate down
  reproductive tract from ampulla through oviduct
  toward uterus
• Embryonic Development see diagram (slide 11)
• Cleavage is initiated
• 2 cell- 4 cell- 8 cell (morula)
• 8-32 cell- the zygote leaves oviduct and goes to
  uterus
• -occurs 2-3 days post-conception in the sow and
  ewe
• -occurs 3-4 days post-conception in the cow

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• Note
• If estrogen levels are high, contractions become
  too great and edema closes utero-tubal junction
  so conceptus cant get into uterus
• If progesterone is too high, ovum may be
  transported too quickly due to slower and more
  rhythmic contractions
• Conceptus can catch up with uterus, but uterus
  cant catch up to conceptus
• -if conceptus gets to uterus too quickly, uterus
  will not be ready to accept it.

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• Note
• Implications with embryo transfer
• -Time to do embryo transfer 6-7 days
  post-breeding
• Minimum of 4 embryos in the sow by day 10-15 in
  order for maternal recognition to occur
• Migration between uterine horns
• -Pig
• -Mare

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Transuterine Migration

• Important in Pigs Mares
• Migration and spacing is completed in sow by Day
  12 in the sow
• Transuterine migration occurs 13x/day between Day
  10 and Day 16 in mares

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• In cow and sheep strong tendency in both
  species when a single ovum is released, the
  conceptus remains in horn on ovulating side.
• 643 monovulvar cows carrying a single fetus had
  0 transuterine migration 8 of 843 ewes with
  single ovulations had migration.
• 10 cows with 2 CL on same ovary with 2 fetuses
  had a 20 transuterine migration
• 120 ewes 2 Cl on same ovary 2 fetuses
  87.5 migration

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Maternal Recognition of Pregnancy

• Species Factor RecognitionTime
• Cow bTP-1 15-18 post ovul.
• Ewe oTP-1 12-14 post-ovul
• Sow Estradiol 13-15 post-ovul
• endocrine-exocrine theory
• Mare 3 proteins/Estrogens 12-14

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Maternal Recognition

• Maternal recognition must occur before luteolysis
• In the cow and ewe, the blastocyst (via
  interferons) blocks the synthesis of uterine
  oxytocin receptors by the endometrial cells of
  pregnant uterus
• Interferons are nonspecific glycoproteins from
  white blood cells and trophoblastic cells-also
  promotes protein synthesis by uterine
  glands-impotant for early embryo survival

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Maternal Recognition

• 4. In the sow estradiol reroutes the secretion of
  PGF2? by the endometrium to the uterine lumen.
  Absence of conceptus allows the PGF2? to flow
  back to the ovary and regress the CL
• 5. In the sow there must be two fetuses in each
  uterine horn for maternal recognition of
  pregnancy to occur. If so, why is it possible for
  some sows to only give birth to 1-3 piglets
• The net effect of maternal recognition of
  pregnancy is the maintenance of high levels of
  blood progesterone

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Maternal recognition of pregnancyDays 12 to 17

• During this stage the embryos increase their
  production of estrogens which is a signal for the
  dam to recognize pregnancy.
• At least 2 embryos must be present in each horn
  for this signal to be recognized by the dam.

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Maternal Recognition of Pregnancy

• Pig E2 by conceptus
• exocrine (pregnant)
• PGF2a
• endocrine (open)
• Cow and sheep
• -placentolactogen secreted by conceptus
• -blocks luteolysis

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Implantation

• The embryo is said to be implanted or attached
  when it becomes fixed in position and physical
  contact with maternal organism is established
• The loose and gradual nature of the attachment
  processes in farm mammals has led to considerable
  controversy about when implantation actually
  begins. Estimates have ranged from the 10th to
  the 22nd day p.c. for sheep and from the 11th to
  the 40th day in cattle.

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Implantation

• Types of Implantation (Attachment)
• Eccentric -Rodents
• Central -Livestock
• Interstitial -Primates

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Types of Implantation

• 1. Eccentric rat embryo enters a crypt or
  fold of the uterus decidualization
• 2. Central cow., ewe, sow conceptus lies
  along the endometrial epithelium
• 3. Interstitial human (primate) invasion of
  conceptus into the endometrial wall of the uterus

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1. Eccentric - rat
placenta
crypt
embryo
decidualization
2. Central - cow, ewe, pig
Endometrium Epithelium
3. Interstitial - Primates
Endo-
invasion
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Occurs when?

• Sow -Starts at Day 13
• -Completed by Day 18-24
• Ewe -Usually around Day 25
• Cow -Day 35-37
• Mare -Days 24-40

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Time of Implantation

• Varies with
• Inherent genetic constitution
• Variation in availability and utilization of
  metabolic materials
• Preparative state of the endometrium

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• Shortest elapsed time between fertilization and
  implantation
• Mouse, rat 6 days
• Bat 16 days
• Period in ungulates is long and variable. Pig is
  shorter than some carnivores

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Spacing

• In sheep with a single CL, blastocysts rarely
  pass from one horn to another. If 2 ova are
  released from the same ovary, migration of one to
  the contralateral horn almost always occurs.
• In pigs, if all eggs were to come from one ovary
  proportion of total uterus occupied increases
  from 13 on the 6th day to 86 on the 12th day.
• In pigs, distribution is more even than just by
  chance alone. An implanting blastocyst appears to
  have no inhibitory effect on its neighbor

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Placentation

• -Development of extraembryonic membranes
• -amnion -ectoderm mesoderm
• -1o function is to protect the embryo
• -chorion -ectoderm and mesoderm
• -undermost layer
• -allantois -endoderm mesoderm
• -exportion to fill chorionic cavity
• -Chorioallantoic membrane forms final portion of
  placenta

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Placental Types

• Classification
• Shape- diffuse
• cotyledonary
• zonary
• discoid
• Maternal-fetal relationship
• a) epitheliochorial- pigs, mares
• b) syndesmochorial- cows, ewes, deer
• c) endotheliochorial- rodents
• d) hemochorial-human female, monkey

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• Freemartinism
• -occurs in female member of heterosexual bovine
  twins in which chorionic membranes of the twins
  fuse(anastomosis)

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Factors affecting length of gestation

• Age of Dam young heifers shorter gestations-
  ewe lambs have 4-5 days less gestation
• Other factors
• Litter size larger litter size shorter
  gestation
• Male- 1-2 days longer
• Endocrine factor

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• 3) Genetic factors
• dairy cows longer gestation
• certain genotypes
• nutrition
• temperature higher ambient temperature
  shorter gestation
• season shorter in autumn and summer