Advanced Reproduction Physiology (Part 3)
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Transcript of 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. Riasihttp://riasi.iut.ac.ir
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Physiology of Pregnancy and Embryo Development
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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
Spermatozoa in female tract
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Two stages for spermatozoa transport:
Rapid transport
Oxytocin secretion
Prostaglandins
Sustained transport
Spermatozoa in female tract
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Factors may affect spermatozoa transport in
cervix:
Sperm motility
Physicochemical change in cervix secretions
Spermatozoa in female tract
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Spermatozoa in female tract
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Sperm capacitation:
Chemical changes
Remove decapacitation factors
Remove cholesterol
Membrane ions changes
Physical and morphological changes
Spermatozoa in female tract
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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.
Spermatozoa in female tract
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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.
Spermatozoa in female tract
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Altering the lipid composition of sperm plasma
membranes affects:
The ability of sperm to capacitate
Acrosomal reaction
Respond to cryopreservation.
Spermatozoa in female tract
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High intracellular concentrations of Ca2+,
HCO3− and K+ are required for:
Acrosome reaction
Fuse with the oocyte.
Spermatozoa in female tract
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Physical and morphological changes:
Spermatozoa in female tract
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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.
The oocyte moving in female tract
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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.
Sperm penetration
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A spermatozoon has to penetrate four layers
before it fertilizes the oocyte:
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
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Three changes occur in the oocyte after
penetration of vitelline membrane:
Sperm penetration
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Fertilization has two important genetic
consequences:
The diploid chromosome number is restored (2n).
The genetic sex of the zygote is determined
Fertilization
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Fertilization
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Cleavage
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Cleavage
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Cleavage
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Embryonic mortality in the initial seven days of
gestation:
Fertilization failure
Genetic defects
Impaired embryonic development
Increase conception rate
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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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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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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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Decrease the effects of a dominant follicle during
the critical period
Antiluteolytic stimulus provided by the conceptus
Decrease uterine luteolytic capacity
Increase conception rate
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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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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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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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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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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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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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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.
Increase conception rate
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One possible hormone injection and TAI schedule for the Presynch/Ovsynch protocol based on the results of Moreira et al., 2000
Increase conception rate
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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.
Increase conception rate
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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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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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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).
Increase conception rate
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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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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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Antiluteolytic strategies:
Pharmacological
Mechanical
Nutritional
Management
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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.
Increase conception rate
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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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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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Pharmacological strategies
The GnRH-hCG treatment
It induced an increase in plasma progesterone
concentrations
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Antiluteolytic strategies:
Antiinflamatory drugs
Fat feeding
Bovine somatotropin (bST)
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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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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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Fat feeding influences several aspects of
reproduction in cattle
(See review by Santos et al., 2008).
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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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Strategies for growth of the conceptus
Secretion of IFN is positively associated with
conceptus size.
Administration of bST.
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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.
Maternal recognition of pregnancy
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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.
Maternal recognition of pregnancy
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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.
Maternal recognition of pregnancy
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The ways in which different species:
In human
Luteolysis is initiated by an intraovarian mechanism,
although many believe it requires local production of
PGF2α.
Maternal recognition of pregnancy
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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 PGF2α
Maternal recognition of pregnancy
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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 PGF2α 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 PGF2α.
Maternal recognition of pregnancy
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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
Maternal recognition of pregnancy
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Importance of progesterone:
Some factors may affect the metabolism and
excretion of progesterone:
Feed intake
Milk yield
Administration of exogenous progesterone
Maternal recognition of pregnancy
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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.
Embryonic loss
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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.
Embryonic loss
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Injection interferons have ability to improve
pregnancy success in ewes may be due:
The rescue of embryos delayed.
Embryonic loss
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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
Embryonic loss
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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.
Pregnancy-Associated Glycoproteins (PAG)
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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.
Pregnancy-Associated Glycoproteins (PAG)
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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.
Pregnancy-Associated Glycoproteins (PAG)
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The PAG have a well-defined peptide- binding
cleft.
They are relatively hydrophobic polypeptides.
They are unlikely to have enzymatic activity.
Pregnancy-Associated Glycoproteins (PAG)
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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
Pregnancy-Associated Glycoproteins (PAG)
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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.
85:122–131.
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: 945–954.
3- De Rensis, et al. 2008. Inducing ovulation with hCG improves the fertility
of dairy cows during the warm season. Theriogenology 69: 1077–1082
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: 1026–1037.