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Reproductive Physiology

Reproductive Physiology. What in the World is Going on in There!. Hypothalamus. Located at the base of the forebrain Receives and interprets both sensory and hormonal cues Secretes gonadotropin -releasing hormone ( GnRH ) into the portal vascular system of the median eminence.

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Reproductive Physiology

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  1. Reproductive Physiology What in the World is Going on in There!

  2. Hypothalamus • Located at the base of the forebrain • Receives and interprets both sensory and hormonal cues • Secretes gonadotropin-releasing hormone (GnRH) into the portal vascular system of the median eminence. • Two modes of GnRH release; pulsatile and surge

  3. Endocrinology Gonadotropin-releasing Hormone (GnRH) Actions • Pulsatile release stimulates similar pulses of pituitary hormones which supports the growth and endocrine function of both follicles and the corpus luteum. • A surge of GnRH stimulates a surge release of pituitary hormones that induces rupture of a follicle (ovulation) and subsequent formation of a CL.

  4. GnRH

  5. Pituitary • Response organ to the hypothalamus and ovaries • Secretes luteinizing hormone (LH) and follicle stimulating hormone (FSH) in response to GnRH from the hypothalamus

  6. Endocrinology Luteinizing Hormone (LH) [yellowing hormone] Origin • Gonadotrophic cells of the anterior pituitary • GnRH release from the hypothalamus stimulates release of LH Actions • Two modes of release for LH; pulsatile and surge. • Pulses of LH stimulates follicle and CL growth and endocrine function • A surge of LH stimulates follicle rupture and release of the oocyte (ovulation)

  7. 5 10 15 Luteinizing Hormone (LH) Ovulation Ovulation GnRH Pituitary LH Hormone Concentration Estrus Estrus Days Relative to Estrus

  8. Endocrinology Follicle Stimulating Hormone (FSH) Origin • Gonadotrophic cells of the anterior pituitary • GnRH release from the hypothalamus stimulates production of FSH. Release controlled by hormones from follicle. Action • FSH is released in small surges that precede the onset of follicle growth.

  9. 5 10 15 Follicle Stimulating Hormone (FSH) Ovulation Ovulation Hormone Concentration Estrus Estrus Days Relative to Estrus

  10. GnRH LH and FSH +

  11. Ovarian Structures • Follicles • Balloon-like structures • Contain the oocyte (egg) • Produces estrogen • Corpus Luteum (CL) • Solid structure • Produces progesterone

  12. The Ovarian Cycle – Growth of the CL Estrus Estrus

  13. 15 5 10 Waves of Follicular Development Ovulation Ovulation 2nd 1st Wave Wave Hormone Concentration Estrus Estrus Days Relative to Estrus

  14. Endocrinology Estrogen (estrus generating hormone) Origin • Produced by growing follicles on the ovary • As follicle increases in size, its production of estrogen increases Actions • Stimulates behavioral estrus • Stimulates LH surge which results in follicle rupture and release of the oocyte (ovulation)

  15. 5 10 15 Pattern of Estrogen Ovulation Ovulation Hormone Concentration Follicles Estrogen Estrus Estrus Days Relative to Estrus

  16. 5 10 15 Follicle Growth and Estrogen Concentrations 2nd 1st Wave Wave Ovulation Hormone Concentration Estrogen Estrus Estrus Days Relative to Estrus

  17. Endocrinology Progesterone (Pro gestational hormone) Origin • Produced by the corpus luteum (CL) • As CL size increases its production of progesterone increases Actions • Controls LH pulse frequency; 4-6 per day • Inhibits the final development of dominant follicles and thus the expression of estrus • Vital for maintenance of pregnancy

  18. 5 10 15 Production of Progesterone by the CL Ovulation Ovulation CLProgesterone Hormone Concentration Estrus Estrus Days Relative to Estrus

  19. 5 10 15 The Ovarian Cycle 2nd 1st Wave Wave Ovulation Hormone Concentration Estrogen Estrus Estrus Days Relative to Estrus

  20. GnRH LH and FSH + Estrogen + Progesterone -

  21. 5 10 15 Steroid Effects on LH Secretion Ovulation Ovulation GnRH Pituitary LH Increased Estrogen Decreased Hormone Concentration Progesterone Estrus Estrus Days Relative to Estrus

  22. Endocrinology Prostaglandin F2α Origin • Produced by the uterus; released in pulses Action • Stimulates the regression of the CL resulting in the expression of estrus and/or ovulation.

  23. 5 10 15 Prostaglandin F2 Ovulation Ovulation Progesterone Hormone Concentration UterusProstaglandin Estrus Estrus Days Relative to Estrus

  24. GnRH LH and FSH + Estrogen + Progesterone - PGF -

  25. 5 10 15 The Estrous Cycle in Cattle LH 2nd 1st Progesterone Wave Wave Hormone Concentration Estrogen FSH Estrus Estrus Days Relative to Estrus

  26. Critical Control Points for Fertility • Expression of estrus; behavior • Breakdown of the hypothalamic-gonadotropic axis. Typically results in altered LH secretion, premature luteinization of follicular cells, premature resumption of meiosis and the oocyte is compromised. • 2 vs 3 waves of follicle growth • Luteal size and progesterone production

  27. Critical Control Points for Fertility • ANESTRUS! • Length of the postpartum or prepubertalanestrus period dramatically impacts the ability of a female to conceive in a controlled breeding season.

  28. Impact of Anestrus HEAT STRESS Conc Rate = 30% Breeding Season Calving Season Gestating Cows Apr Jun Dec Aug Sep Oct Nov Dec Jan Feb Mar May Jul Aug Sep Oct Nov Jan Months

  29. Reproductive Classes Within the Cow Herd 50% 50% Shallow Anestrous Random stages of the cycle Anestrous Cows Cyclic Cows Deep Anestrous

  30. Postpartum Anestrus in Beef Cows Anestrus 25 to 100+ days in US Beef Cows 1st DF * * Follicle Diameter Progesterone Uterine involution and pituitary replenishment Days Relative to Calving Calving First Estrus

  31. Factors Regulating the Length of Anestrus • Presence of the calf • Initiates anestrus • Body Condition Score (BCS) • Age • Days Since Calving • Others effectors include dystocia, health, and calving season

  32. Presence of the Calf • Presence of the calf initiates anestrus • Mechanism unknown but both the physical contact of the calf (nursing) and the mere presence of the calf at side are involved. • Short-term calf removal (48 h) has been shown to be an effective method to induce estrus.

  33. Body Condition Score (BCS) • Body Condition Score is an estimate of the degree of fatness of an animal • 1 = emaciated • 9 = extremely obese • Estimate of available energy stores

  34. Influence of BCS on Anestrus Source: Stevenson et al., 2003

  35. Age • Young cows (2 year old suckled cows) simply require 20-30 more days resume estrous cycles. • Recommendation has always been to calve first calf heifers 20-30 days before the mature cow herd. • Stevenson et al., 2003 Age Days PP Percent Cyclic 2 86 55 3+ 68 64

  36. Influence of Days Since Calving on Anestrus Source: Stevenson et al., 2003

  37. Summary • Reproductive physiology……clear as mud! • Critical control points for fertility: • Expression of estrus • Disruption of the HPG axis • Number of follicle waves • Luteal size and progesterone production • Length of the postpartum anestrous period.

  38. Anatomy and Physiology of the Pregnancy and the Calving Process

  39. Fertilization • Occurs in the oviduct at the ampulla-isthmus junction • Zygote is the term for a newly fertilized oocyte; only has 1 cell • An embryo is the term used after the zygote has begun cellular divisions. • Embryos migrate from the oviduct about 5 days after fertilization.

  40. Embryo Development 8 cell - D 4 Morula - D 6 Early Blastocyst – D 6-7 Blastocyst – D 6-7 Hatching Blastocyst – D7-8

  41. Pregnancy • Stages: • Embryo - fertilization to app. D 30 • Fetus - Day 30 of pregnancy to parturition • Components of a pregnancy: • Fetus/embryo • Placenta • membranes responsible for the protection and nourishment of the fetus • Amnion directly surrounds the fetus; Chorio-allantoic extends throughout the uterus

  42. Pregnancy • Placenta • Membranes • Amnion directly surrounds the fetus to protect it • Chorion (chorio-allantoic) extends throughout the uterus and its primary role is nutrient transfer to the fetus. • Nutrient transfer occurs at specialized structures called placentomes. The maternal side is called a caruncle, the fetal side is called the cotyledon.

  43. Anatomy of Pregnancy

  44. Pregnancy • Parturition (birthing) • Stimulated by the fetus • fetus cortisol • placenta Prostaglandin F ovary CL regresses, releases oxytocin, relaxin Uterus contractions begin

  45. General Repro Statistics • Estrous Cycle Length = 21 days; range 17-24 • Length of estrus = 12 hours; range 6-24 • Ovulation = 10-12 hours after the end of estrus or 30 hours after beginning of estrus; range 18-48 • Gestation length = 283; range 260-300

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