Advanced reproductive Physiology By: A. Riasi (PhD in Animal Nutrition & Physiology)...

Advanced reproductive

Physiology

By: A. Riasi (PhD in Animal Nutrition &

Physiology)

فیزیولوژی تولید مثل پیشرفته

At the end of this section students will be able to reply

How NEB affect the reproductive performance of dairy cows?

Which factors may affect the twining rate in dairy cattle?

Does nutrition affect postpartum cyclicity resumption and

duration of estrus?

What are physiological changes in postpartum dairy cows

How leptin affect the hypothalamus and pituitary gland?

What is early embryonic loss?

Infertility in Dairy cows

The reproductive genotype of dairy cows is

normal and their reproductive phenotype is a

function of lactation.

Dairy cows faced to negative energy balance

during the early lactation period.

Infertility in Dairy cows

The metabolic and endocrine cues associated

with negative energy balance impair:

Resumption of ovulatory cycles

Oocyte and embryo quality

Formation a corpus luteum

Establishment and maintenance of pregnancy

Relationship between the BCS and anovular cows in a U.S. herd

Increase milk

production

Prolactin Somatotropin Insulin

Endocrine change

We need to know how nutrition can affect

reproduction, for better or for worse.

Providing a balanced diet to females is most critical

During the last trimester of pregnancy

Through the breeding season

Among the functions fueled by nutrients, reproduction

typically takes a back seat.

Some nutritional solution for thin dairy cows

Maximizing DMI during the transition period

Minimizing the incidence of peri-parturient problems

Adding supplemental fat to diets

Manipulating the FA content of fat sources

It is appear nutrition affect:

Cyclicity

Follicular development

Oocyte quality

Gene expression

Short-term nutritional manipulations may be

designed to enhance pregnancy rates.

The Bcl-2 gene family members are involved in:

Cell proliferation

Follicular selection

Luteolysis

The ratio between Bcl-2/BAX shows to be critical

for the normal survival of germ cells.

One of reproductive trait that has been directly

linked to milk production is double ovulation rate.

For a more complete review see Lopez et al., 2005;

Wiltbank et al., 2000.

Numerous factors that regulate twinning rate:

Age of dam

Season

Genetics

Use of reproductive hormones or antibiotics

Ovarian cysts

Days open

Peak milk production *

Effect of parity on twining rate (%) and relative risk of twining in

dairy cattle.

Adapted from Wiltbank et al., 2000

Adapted from Wiltbank et al., 2000

Does nutrition affect postpartum

cyclicity resumption and duration of

estrus?

Anovular cows have:

Reduced estrous detection

Reduced conception rates

Compromised embryo survival

Energy deprivation reduces the frequency of pulses

of LH.

Under-nutrition inhibits estrous behavior.

What are physiological changes in

postpartum dairy cows?

There are two phases in postpartum

reproduction recovery:

Resumption of FSH and LH pulsatility and

reestablishment of LH surge mechanism

Uterine involution

Follicular development begins shortly after

calving with a transient increase in FSH.

However the first postpartum dominant follicle

undergoes one of three fates:

Ovulation

Atresia and turnover

Cyst formation

Some endocrine hormones can influence GnRH

secretion.

The actions may be on:

GnRH neurons

The neuronal pathways that impinge upon GnRH

neurons

The pituitary gonadotroph

The hormonal control arises from tissues that

respond to the metabolic or nutritional status:

Pancreas with secretion insulin

Liver with secretion IGF-I

Adipose tissue with secretion leptin

The metabolites and hormones that influence on

GnRH may act directly on sensitivity of the ovary

to LH and FSH.

Insulin and IGF-1 may affect the ovaries

independent of LH and FSH

The increased incidence of anestrus and

abnormal estrous cycles:

LH secretion

Metabolic growth factors

Follicular development

Estradiol secretion

Lower metabolic hormone concentrations may

contribute to a decrease in ovarian LH

responsiveness.

Lactating cows had larger preovulatory

follicles than heifers but lower preovulatory

concentrations of estradiol in blood. Why?

What is early embryonic loss?

From conception to the time of maternal

recognition of pregnancy, embryonic loss is high.

The early embryonic loss is affected by:

Nutritional factors

Reproductive management

The relationship of body condition score and

early embryonic loss (Mapletoft et al. 1986)

Energy deficiency should be considered as a

problem in herds, in this condition:

Cows lose excessive amounts of body condition

during early lactation.

Cows are not cycling normally by 30-40 days after

calving.

Cows in better energy balance had greater

intrafollicular IGF-I and plasma progesterone

levels and produce more oocytes graded as good.

Therefore, NEB not only delays resumption of

ovulatory cycles but it might also influence the

quality of occytes once cows are inseminated.

When heifers are fed inadequate amounts of

energy, they reach sexual maturity later.

If energy deficient rations are fed to heifers that

have begun to have normal estrous cycles, they

may stop cycling.

The first key is to understand the nutrient needs

of cattle at different phases of production and

reproduction.

The second key is to know the nutrition content

of the predominate feedstuff and supplement as

needed.

The primary nutrients that should be considered

in providing for good reproduction are:

Energy

Protein

Minerals

Vitamins

Fiber

Energy intake may be the most important

nutritional factor affecting reproduction.

Excessive energy intake during late lactation

and the dry period can cause “fat cow” problems

In cows with NEB, blood concentration of

NEFA icrease and at the same time IGF-I, glucose

and insulin are low.

It has shown cyclic cattle that are underfed have

progressively smaller and less estrogenic dominant

follicles (Bossis et al., 1999).

Poor nutrition

Low energy intake

Lower metabolic hormones:• Somatotropin• Insulin• IGF-I

Lower progesterone concentration in blood

Smaller and less estrogenic dominant follicle

Smaller corpora lutea

Lower sroidogenic capacity of corpora lutea

Lower reproduction performance

Expression of hepatic growth hormone receptor

(GHR-1A) is thought to be responsible for the

concentrations of IGF-I in plasma of cows.

IGF-I is an important hormonal signal that

influences reproductive events:

Stimulation of cell mitogenesis

Hormonal production

Embryo development

Feeding diets that promote greater insulin

concentrations are benefit for fertility.