Download - Advanced reproductive Physiology (part 2)
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Advanced reproductive
Physiology
By: A. Riasi (PhD in Animal Nutrition &
Physiology)
فیزیولوژی تولید مثل پیشرفته
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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?
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Infertility in Dairy cows
The reproductive genotype of dairy cows is
normal and their reproductive phenotype is a
function of lactation.
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Dairy cows faced to negative energy balance
during the early lactation period.
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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
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Relationship between the BCS and anovular cows in a U.S. herd
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Increase milk
production
Prolactin Somatotropin Insulin
Endocrine change
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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.
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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
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It is appear nutrition affect:
Cyclicity
Follicular development
Oocyte quality
Gene expression
Short-term nutritional manipulations may be
designed to enhance pregnancy rates.
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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.
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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.
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Numerous factors that regulate twinning rate:
Age of dam
Season
Genetics
Use of reproductive hormones or antibiotics
Ovarian cysts
Days open
Peak milk production *
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Effect of parity on twining rate (%) and relative risk of twining in
dairy cattle.
Adapted from Wiltbank et al., 2000
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Adapted from Wiltbank et al., 2000
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Does nutrition affect postpartum
cyclicity resumption and duration of
estrus?
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Anovular cows have:
Reduced estrous detection
Reduced conception rates
Compromised embryo survival
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Energy deprivation reduces the frequency of pulses
of LH.
Under-nutrition inhibits estrous behavior.
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What are physiological changes in
postpartum dairy cows?
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There are two phases in postpartum
reproduction recovery:
Resumption of FSH and LH pulsatility and
reestablishment of LH surge mechanism
Uterine involution
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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
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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
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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
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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
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The increased incidence of anestrus and
abnormal estrous cycles:
LH secretion
Metabolic growth factors
Follicular development
Estradiol secretion
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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?
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What is early embryonic loss?
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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
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The relationship of body condition score and
early embryonic loss (Mapletoft et al. 1986)
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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.
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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.
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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.
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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.
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The primary nutrients that should be considered
in providing for good reproduction are:
Energy
Protein
Minerals
Vitamins
Fiber
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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
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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).
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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
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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
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Feeding diets that promote greater insulin
concentrations are benefit for fertility.