Advanced Reproduction Physiology (Part 3)

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Advanced Reproduction Physiology(Part 3)

• Isfahan University of Technology
• College of Agriculture, Department of Animal
  Science

Prepared by A. Riasi http//riasi.iut.ac.ir
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Physiology of Pregnancy and Embryo Development
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Spermatozoa in female tract

• In natural mating semen are introduced in
• Vagina
• Cervix
• Within the female tract spermatozoa are lost by
• Phagocytosis by neutrophils
• Physical barrier including the cervix

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Spermatozoa in female tract

• Two stages for spermatozoa transport
• Rapid transport
• Oxytocin secretion
• Prostaglandins
• Sustained transport

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Spermatozoa in female tract

• Factors may affect spermatozoa transport in
  cervix
• Sperm motility
• Physicochemical change in cervix secretions

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Spermatozoa in female tract
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Spermatozoa in female tract

• Sperm capacitation
• Chemical changes
• Remove decapacitation factors
• Remove cholesterol
• Membrane ions changes
• Physical and morphological changes

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Spermatozoa in female tract

• Higher levels of FPP prevent capacitation
• FPP is found in the seminal fluid and comes into
  contact with the spermatozoa upon ejaculation.
• It has a synergistic stimulatory effect with
  adenosine that increases adenylyl cyclase
  activity in the sperm.

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Spermatozoa in female tract

• Other chemical changes
• Removal of cholestrol and non-covalently bound
  epididymal/seminal glycoproteins is important.
• The result is an increased permeability of sperm
  to Ca2, HCO3- and K
• An influx of Ca2 produces increased
  intracellular cAMP levels.

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Spermatozoa in female tract

• Altering the lipid composition of sperm plasma
  membranes affects
• The ability of sperm to capacitate
• Acrosomal reaction
• Respond to cryopreservation.

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Spermatozoa in female tract

• High intracellular concentrations of Ca2, HCO3-
  and K are required for
• Acrosome reaction
• Fuse with the oocyte.

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Spermatozoa in female tract

• Physical and morphological changes

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The oocyte moving in female tract

• Oocyte is transported by cilia of oviduct.
• Smooth muscles of oviduct adjust the time of
  oocyte transportation.
• The mature egg can only survive for about 6
  hours, so the time of insemination is important.

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Sperm penetration

• A series of events
• First step acrosome reaction
• After the reaction, the vesicles are sloughed,
  leaving the inner acrosomal membrane and the
  equatorial segment intact.

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Sperm penetration

• A spermatozoon has to penetrate four layers
  before it fertilizes the oocyte

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Sperm penetration
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Sperm penetration
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Sperm penetration
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Sperm penetration
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Sperm penetration

• Three changes occur in the oocyte after
  penetration of vitelline membrane

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Fertilization

• Fertilization has two important genetic
  consequences
• The diploid chromosome number is restored (2n).
• The genetic sex of the zygote is determined

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Fertilization
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Cleavage
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Cleavage
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Cleavage
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Increase conception rate

• Embryonic mortality in the initial seven days of
  gestation
• Fertilization failure
• Genetic defects
• Impaired embryonic development

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Increase conception rate

• Measuring embryonic mortality in weeks two and
  three of gestation is much more challenging.
• This period coincides with the maternal
  recognition of pregnancy.

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Increase conception rate

• Successful establishment of pregnancy depends on
  a delicate balance between
• Luteolytic mechanisms inherent to the endometrium
  at the end of diestrus.
• Antiluteolytic mechanisms, orchestrated by the
  conceptus.

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Increase conception rate

• Some strategies for increasing conception rate
• Using TAI protocols
• Stimulate growth and/or differentiation of the
  pre-ovulatory follicle
• Stimulate CL growth rate
• Increase plasma progesterone concentrations in
  the initial three weeks after insemination.

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Increase conception rate

• Decrease the effects of a dominant follicle
  during the critical period
• Antiluteolytic stimulus provided by the conceptus
• Decrease uterine luteolytic capacity

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Increase conception rate

• Reproductive physiologists had long searched to
  develop a synchronization program.
• Ovsynch synchronizes AI at a fixed-time without
  the need for estrus detection.

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Increase conception rate

• Some factors may affect Ovsynch results
• The stage of the estrous cycle
• Cyclic status at the time that GnRH is
  administered (Bisinotto et al., 2010)

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Increase conception rate

• Researchers have modifed the original Ovsynch
  protocol to try to
• Improve synchrony and fertility through
  presynchronization
• Altering the timing of AI in relation to
  ovulation
• Testing the various injection intervals of the
  original protocol

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Increase conception rate

• TAI programs need day-to-day operation, so it may
  use for
• Lactating dairy cows with little or no estrus
  detection at all
• Voluntary Waiting Period (VWP)

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Increase conception rate

• Factors explaining the variation in conception
  rate to TAI among herds may include
• The proportion of anovular cows
• The follicular dynamics of individual cows
• The ability of farm personnel to implement
  Ovsynch

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Increase conception rate

• Following this first report, numerous protocols
  have been proposed and routinely applied in high
  production dairy cows (Wiltbank et al., 2011).

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Increase conception rate

• Programming cows for first postpartum AI using
  presynch/ovsynch
• Use of presynch for programming lactating dairy
  cows to receive their first postpartum TAI can
  improve first service conception rate in a dairy
  herd.

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Increase conception rate
One possible hormone injection and TAI schedule
for the Presynch/Ovsynch protocol based on the
results of Moreira et al., 2000
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Increase conception rate

• In an assay, cycling cows conception rate was
  29 for Ovsynch and 43 for Presynch.
• These protocols may presents low efficiency when
  applied in tropical condition.

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Increase conception rate

• Estradiol plus progesterone based protocol
• Exogenous P4 and progestins has consequences
• Suppresses LH release
• Alters ovarian function
• Suppresses estrus
• Prevents ovulation

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Increase conception rate

• Novel studies introduced the use of E2 plus P4 to
  control follicular wave dynamics (Sá Filho et
  al., 2011)
• Several studies found that E2 plus P4 treatment
  suppress the growing phase of the dominant
  follicle.
• The interval from E2 treatment to follicular wave
  emergence seemed to depend on FSH resurgence
  (O'Rourke et al., 2000).

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Increase conception rate

• In E2 plus P4 protocols, a lower dose of E2 is
  normally given from 0 to 24 h after progestin
  removal to induce a synchronous LH surge (Hanlon
  et al., 1997 Lammoglia et al., 1998 Martínez et
  al., 2005 Sales et al., 2012).

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Increase conception rate

• Anestrous cows have insufficient pulsatile
  release of LH to support the final stages of
  ovarian follicular development and ovulation.
• What we should do for anestrous cows?
• The treatment with equine chorionic gonadotropin
  (eCG) may be effective.

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Increase conception rate

• eCG administration for anestrous or low BCS dairy
  cows has benefit effects (Souza et al., 2009
  Garcia-Ispierto et al., 2011).

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Increase conception rate

• Antiluteolytic strategies
• Pharmacological
• Mechanical
• Nutritional
• Management

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Increase conception rate

• Strategies to increase progesterone
• Daily injection of progesterone
• Using of progesterone releasing intravaginal
  device (PRID)
• Inducing the formation of accessory corpora lutea
  by the ovulation of the first wave dominant
  follicle.

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Increase conception rate

• Effect of estrogen
• Inskeep (2004) indicated that estrogen secretion
  from a large follicle from days 14 to 17 of
  pregnancy may negatively affect embryo survival.
• This hormone has a central role in PGF production
  and luteolysis.

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Increase conception rate

• Some strategies for reducing estrogent
• Absence of dominant follicles
• Reduction of their steroidogenic capacity
• Reduction of endometrial responsiveness to
  estradiol during the period of maternal
  recognition of pregnancy
• Pharmacological approaches

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Increase conception rate

• Pharmacological strategies
• The GnRH-hCG treatment
• It induced an increase in plasma progesterone
  concentrations

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Increase conception rate

• Antiluteolytic strategies
• Antiinflamatory drugs
• Fat feeding
• Bovine somatotropin (bST)

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Increase conception rate

• Synthesis of PGF results from a coordinated
  cascade of intracellular events.
• A rate limiting step in this cascade is the
  conversion of arachidonic acid to
  prostaglandin-H2 (PGH).

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Increase conception rate

• The key enzyme is PTGS2 or COX-2.
• The PGH is subsequently converted to PGF.
• Guzeloglu et al. (2007) treated Holstein heifers
  with flunixin meglumine, a non-steroidal
  antiinflamatory drug which inhibits PTGS2
  activity, on days 15 and 16 after insemination.

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Increase conception rate

• Fat feeding influences several aspects of
  reproduction in cattle
• (See review by Santos et al., 2008).

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Increase conception rate

• Feeding long chain fatty acids can modulate PGF
  production in the endometrium.
• Effect of n-3 fatty acids (Mattos et al., 2003,
  2004)
• Effect of N-6 fatty acids (Pettit and
  Twagiramungu, 2004)
• A summary of the effects of fatty acid feeding on
  cattle fertility reported by Santos et al. (2008).

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Increase conception rate

• Strategies for growth of the conceptus
• Secretion of IFN is positively associated with
  conceptus size.
• Administration of bST.

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Maternal recognition of pregnancy

• Mother quickly becomes cognizant of the
  cleavage-stage embryo within her body.
• Mother reacts to embryo presence, but its not
  enough for the pregnancy to proceed.

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Maternal recognition of pregnancy

• For maternal recognition it is necessary
• The normal cyclic regression of CL be prevented
  in order to maintain progesterone production.
• The conceptus has also to ensure that an adequate
  supply of maternal blood reaches the sites of
  placentation.

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Maternal recognition of pregnancy

• The conceptus is recognized as foreign by the
  mother and it must nevertheless take steps to
  avoid a losing confrontation with the maternal
  immune system.
• The conceptus does not become vascularized by the
  host's blood supply.

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Maternal recognition of pregnancy

• The ways in which different species
• In human
• Luteolysis is initiated by an intraovarian
  mechanism, although many believe it requires
  local production of PGF2a.

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Maternal recognition of pregnancy

• Luteolysis in these species is avoided by the
  intervention of chorionic gonadotrophin (CG)
• The CG probably binds to LH receptors
• The CG can stimulates progesterone production
• The CG exerts a protective action against PGF2a

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• In rodents
• Rodent do not produce a CG at all.
• During pseudopregnancy in the rat, the cycle is
  lengthened to 12 days before the CL regress.
• This extension of CL life span is the result of
  surges of pituitary prolactin release.
• If the rat is pregnant, a series of placental
  lactogens and prolactin-like hormones produced by
  the placenta.

Maternal recognition of pregnancy
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• In pigs
• Estrogen released by the trophoblast as it begins
  to elongate is probably the initial signal to the
  mother that she is pregnant.

Maternal recognition of pregnancy
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• In horses
• The equine conceptus forms an encapsulated
  spherical structure between days 12 and 14.
• The constant patrolling may be the key to the
  mechanism that inhibits PGF2a release.

Maternal recognition of pregnancy
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• In cattle and sheep
• The conceptus begins to intervene in the
  luteolytic process three to four days before the
  CL actually become dysfunctional.
• In these species, the antiluteolytic substance,
  an unusual Type I interferon (IFN)-t, has been
  reviewed on numerous occasions in the literature.
• Its presence in the lumen clearly suppresses the
  normal pattern of pulsatile release of PGF2a.

Maternal recognition of pregnancy
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Maternal recognition of pregnancy

• Importance of progesterone
• The concentrations of progesterone at a critical
  time before implantation is important for cows
  pregnancy.
• Two logical possibilities for lower progesterone
  in the lactating dairy cows
• Secretion by the corpus luteum is reduced
• Metabolism of progesterone is increase

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Maternal recognition of pregnancy

• Importance of progesterone
• Some factors may affect the metabolism and
  excretion of progesterone
• Feed intake
• Milk yield
• Administration of exogenous progesterone

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Embryonic loss

• Much prenatal mortality occurs in all mammals.
• Higher amount of embryonic wastage occurs
  following IVF and ET.
• The majority of these losses occur prior to or
  during implantation.

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Embryonic loss

• Embryonic losses in sheep and cattle
• It most occurring in the first 3 wk of pregnancy.
• Natural asynchronies
• The late onset of the first meiotic division may
  lead to some oocytes being delayed in their
  maturation.
• A second natural cause of asynchrony may be due
  to delayed fertilization.
• Finally, embryos are known to cleave at different
  rates.

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Embryonic loss

• Injection interferons have ability to improve
  pregnancy success in ewes may be due
• The rescue of embryos delayed.

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Embryonic loss

• Pig conceptuses attain control over maternal
  progesterone production
• Releasing estrogen and probably other factors
  just prior to the time the CL would normally
  regress.
• The second consequence is that it induces the
  massive release of uterine secretions from the
  uterine glandular and surface epithelium

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Pregnancy-Associated Glycoproteins (PAG)

• In 1982 the partial purification and
  characterization of a pregnancy-specific protein
  (PSP-B) was reported from cattle.
• More recently, isolated several isoforms of PAG
  from bovine placental tissue.

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Pregnancy-Associated Glycoproteins (PAG)

• It is now clear that PSP-B and PAG-1 are
  identical in sequence.
• The presence of PAG-1 (or PSP-B) in blood serum
  has provided the basis of a potentially useful
  pregnancy test in cattle.

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Pregnancy-Associated Glycoproteins (PAG)

• The antigen generally becomes detectable by about
  day 20 postbreeding.
• In cattle, concentrations of the antigen rise
  gradually during gestation and peak just prior to
  parturition.

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Pregnancy-Associated Glycoproteins (PAG)

• The PAG have a well-defined peptide- binding
  cleft.
• They are relatively hydrophobic polypeptides.
• They are unlikely to have enzymatic activity.

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Pregnancy-Associated Glycoproteins (PAG)

• Two possible functions for PAG are suggested
• They could be hormones, which, by virtue of their
  binding clefts, are able to bind specific cell
  surface receptors on maternal target cells.
• The second suggestion is that PAG sequestered or
  transported peptides

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Some research papers associated to this lecture
1-Pancarci, et al. 2002. Use of estradiol
cypionate in a presynchronized timed artificial
insemination program for lactating dairy cattle.
J. Dairy Sci. 85122131. 2- Franco, et al.
2006. Effectiveness of administration of
gonadotropin-releasing hormone at Days 11, 14 or
15 after anticipated ovulation for increasing
fertility of lactating dairy cows and
non-lactating heifers. Theriogenology 66
945954. 3- De Rensis, et al. 2008. Inducing
ovulation with hCG improves the fertility of
dairy cows during the warm season. Theriogenology
69 10771082 4- Bartolome, et al. 2005.
Strategic use of gonadotrophin-releasing hormone
(GnRH) to increase pregnancy rate and reduce
pregnancy loss in lactating dairy cows subjected
to synchronization of ovulation and timed
insemination. Theriogenology 63 10261037.