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

 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

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, e mbryonic 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 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.