Isfahan University of Technology
College of Agriculture, Department of Animal Science
Advanced Reproduction
Physiology
(Part 3)
Prepared by: A. Riasi
http://riasi.iut.ac.ir
Physiology of Pregnancy and
Embryo Development
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
Spermatozoa in female tract
 Two

stages for spermatozoa transport:
Rapid transport
 Oxytocin
secretion
 Prostaglandins

Sustained transport
Spermatozoa in female tract
 Factors
may affect spermatozoa transport in
cervix:

Sperm motility

Physicochemical change in cervix secretions
Spermatozoa in female tract
Spermatozoa in female tract
 Sperm

capacitation:
Chemical changes
 Remove
decapacitation factors
 Remove
cholesterol
 Membrane

ions changes
Physical and morphological changes
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.
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.
Spermatozoa in female tract
 Altering
the lipid composition of sperm plasma
membranes affects:
 The
ability of sperm to capacitate
 Acrosomal
 Respond
reaction
to cryopreservation.
Spermatozoa in female tract
 High
intracellular concentrations of Ca2+,
HCO3− and K+ are required for:
 Acrosome
 Fuse
reaction
with the oocyte.
Spermatozoa in female tract
 Physical
and morphological changes:
The oocyte moving in female tract
 Oocyte
 Smooth
is transported by cilia of oviduct.
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.
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.
Sperm penetration
A
spermatozoon has to penetrate four layers
before it fertilizes the oocyte:
Sperm penetration
Sperm penetration
Sperm penetration
Sperm penetration
Sperm penetration
 Three
changes occur in the oocyte after
penetration of vitelline membrane:
Fertilization
 Fertilization
has
two
important
genetic
consequences:

The diploid chromosome number is restored (2n).

The genetic sex of the zygote is determined
Fertilization
Cleavage
Cleavage
Cleavage
Increase conception rate
 Embryonic
mortality in the initial seven days of
gestation:

Fertilization failure

Genetic defects

Impaired embryonic development
Increase conception rate
 Measuring
and
embryonic mortality in weeks two
three
of
gestation
is
much
more
challenging.
 This
period coincides with the maternal
recognition of pregnancy.
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.
Increase conception rate
 Some
strategies for increasing conception rate:

Using TAI protocols

Stimulate growth and/or differentiation of the preovulatory follicle

Stimulate CL growth rate

Increase plasma progesterone concentrations in the
initial three weeks after insemination.
Increase conception rate

Decrease the effects of a dominant follicle during
the critical period

Antiluteolytic stimulus provided by the conceptus

Decrease uterine luteolytic capacity
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.
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)
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
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)
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
Increase conception rate
 Following
this first report, numerous protocols
have been proposed and routinely applied in
high production dairy cows (Wiltbank et al., 2011).
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.
Increase conception rate
One possible hormone injection and TAI schedule for the Presynch/Ovsynch
protocol based on the results of Moreira et al., 2000
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.
Increase conception rate
 Estradiol

plus progesterone based protocol
Exogenous P4 and progestins has consequences:
 Suppresses
LH release

Alters ovarian function

Suppresses estrus

Prevents ovulation
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).
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).
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.
Increase conception rate
 eCG
administration for anestrous or low BCS
dairy cows has benefit effects
Ispierto et al., 2011).
(Souza et al., 2009; Garcia-
Increase conception rate
 Antiluteolytic
strategies:

Pharmacological

Mechanical

Nutritional

Management
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.
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.
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
Increase conception rate
 Pharmacological

strategies
The GnRH-hCG treatment
 It
induced
concentrations
an
increase
in
plasma
progesterone
Increase conception rate
 Antiluteolytic
strategies:

Antiinflamatory drugs

Fat feeding

Bovine somatotropin (bST)
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 prostaglandinH2 (PGH).
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.
Increase conception rate
 Fat
feeding influences several aspects of
reproduction in cattle

(See review by Santos et al., 2008).
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).
Increase conception rate
 Strategies

for growth of the conceptus
Secretion of IFN is positively associated with
conceptus size.

Administration of bST.
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.
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.
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.
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
PGF2α.
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 PGF2α
Maternal recognition of pregnancy

In rodents
 Rodent
 During
do not produce a CG at all.
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

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

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

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
 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
 Importance

of progesterone:
Some factors may affect the metabolism and
excretion of progesterone:
 Feed
intake
 Milk
yield
 Administration
of exogenous progesterone
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.
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.
Embryonic loss

Injection interferons have ability to improve
pregnancy success in ewes may be due:
 The
rescue of embryos delayed.
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
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.
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.
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.
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.
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
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 gonadotropinreleasing 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.