advanced reproduction physiology (part 3)

Advanced Reproduction Physiology

(Part 3)

Isfahan University of Technology

College of Agriculture, Department of Animal Science

Prepared by: A. Riasihttp://riasi.iut.ac.ir

Physiology of Pregnancy and Embryo Development

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


Factors may affect spermatozoa transport in

cervix:

Sperm motility

Physicochemical change in cervix secretions


Sperm capacitation:

Chemical changes

Remove decapacitation factors

Remove cholesterol

Membrane ions changes

Physical and morphological changes


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.


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.


Altering the lipid composition of sperm plasma

membranes affects:

The ability of sperm to capacitate

Acrosomal reaction

Respond to cryopreservation.


High intracellular concentrations of Ca2+,

HCO3− and K+ are required for:

Acrosome reaction

Fuse with the oocyte.


Physical and morphological changes:


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

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

Three changes occur in the oocyte after

penetration of vitelline membrane:

Sperm penetration

Fertilization has two important genetic

consequences:

The diploid chromosome number is restored (2n).

The genetic sex of the zygote is determined

Fertilization

Fertilization

Cleavage

Embryonic mortality in the initial seven days of

gestation:

Fertilization failure

Genetic defects

Impaired embryonic development

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.


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.


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.


Decrease the effects of a dominant follicle during

the critical period

Antiluteolytic stimulus provided by the conceptus

Decrease uterine luteolytic capacity


Reproductive physiologists had long searched

to develop a synchronization program.

Ovsynch synchronizes AI at a fixed-time

without the need for estrus detection.


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)


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


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)


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


Following this first report, numerous protocols

have been proposed and routinely applied in

high production dairy cows (Wiltbank et al., 2011).


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.


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


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.


Estradiol plus progesterone based protocol

Exogenous P4 and progestins has consequences:

Suppresses LH release

Alters ovarian function

Suppresses estrus

Prevents ovulation


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).


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).


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.


eCG administration for anestrous or low BCS

dairy cows has benefit effects (Souza et al., 2009; Garcia-

Ispierto et al., 2011).


Antiluteolytic strategies:

Pharmacological

Mechanical

Nutritional

Management


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.


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.


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


Pharmacological strategies

The GnRH-hCG treatment

It induced an increase in plasma progesterone

concentrations


Antiluteolytic strategies:

Antiinflamatory drugs

Fat feeding

Bovine somatotropin (bST)


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).


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.


Fat feeding influences several aspects of

reproduction in cattle

(See review by Santos et al., 2008).


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).


Strategies for growth of the conceptus

Secretion of IFN is positively associated with

conceptus size.

Administration of bST.


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.


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.


The ways in which different species:

In human

Luteolysis is initiated by an intraovarian mechanism,

although many believe it requires local production of

PGF2α.


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


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.


In pigs

Estrogen released by the trophoblast as it begins to

elongate is probably the initial signal to the mother that

she is pregnant.


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.


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.


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


Importance of progesterone:

Some factors may affect the metabolism and

excretion of progesterone:

Feed intake

Milk yield

Administration of exogenous progesterone


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

Embryonic loss

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.


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.


The PAG have a well-defined peptide- binding

cleft.

They are relatively hydrophobic polypeptides.

They are unlikely to have enzymatic activity.


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 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.

advanced reproduction physiology (part 3)

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