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AVS 222 – Mare Reproductive Physiology and Management

AVS 222 – Mare Reproductive Physiology and Management. Dirk K. Vanderwall Northwest Equine Reproduction Laboratory Department of Animal and Veterinary Science University of Idaho April 21, 2004. Hypothalamus. GnRH. Pituitary Gland. LH. FSH. Ovaries. Progesterone.

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AVS 222 – Mare Reproductive Physiology and Management

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  1. AVS 222 – Mare Reproductive Physiology and Management Dirk K. Vanderwall Northwest Equine Reproduction Laboratory Department of Animal and Veterinary Science University of Idaho April 21, 2004

  2. Hypothalamus GnRH Pituitary Gland LH FSH Ovaries Progesterone Estrogen Female Reproductive Physiology

  3. Hypothalamus GnRH Pituitary Gland LH FSH Ovaries Progesterone Estrogen

  4. Reproductive Seasonality • Physiological breeding season • Ovulatory season • April through September • Physiological non – breeding season • Anovulatory season (anestrus) • December and January • Transitional period • Spring: February and March • Fall: October and November

  5. Reproductive Seasonality Adapted from Ginther, 1974

  6. Reproductive seasonality is regulated primarily by changes in day length

  7. Photoperiod Effect • Reproductive activity in the spring is stimulated by increasing day length • Mechanism involves alteration of hormone secretion by the pineal gland and hypothalamus • Pineal gland: melatonin • Hypothalamus: GnRH • Artificial lighting can be used to hasten the onset of the ovulatory season

  8. Physiological Non – Breeding Season(Winter Anestrus / Anovulatory Season) • Minimal follicular development • GnRH, FSH and LH secretion are low • small, firm ovaries • Follicles < 15 mm in diameter • Mares may exhibit estrous behavior (heat)

  9. Transitional Period • Increased day length stimulates GnRH secretion from the hypothalamus • GnRH stimulates FSH and LH secretion • FSH induces follicular development • Estrogen produced by developing follicles causes the mare to exhibit irregular and / or prolonged estrus • When LH levels have increased, the first ovulation of the year occurs

  10. Transitional Period • 1 to 3 “waves” of follicular growth and regression • Irregular or prolonged estrus • Enlarged ovaries with multiple “clustered” follicles

  11. Physiological Breeding Season • 21 day inter-ovulatory interval (estrous cycle) • Estrus (heat): 5 – 7 days • Ovulation: 24 to 48 hours prior to end of heat • Diestrus: 14 – 16 days

  12. Follicular Dynamics • 1 to 2 waves of follicles emerge during each estrous cycle • Each wave consists of a dominant follicle and several subordinate follicles

  13. Ovulation • LH surge induces final maturation of the follicle and ovulation • The ovulated follicle then develops into a corpus luetum (CL)

  14. Corpus Luteum (CL) Function • The primary function of the CL is the secretion of progesterone, which is necessary for the maintenance of pregnancy

  15. Corpus Luteum Regression • Nonpregnant mares must regress their CL in order to initiate another estrous cycle • The duration of CL function in the nonpregnant mare is 14 to 16 days • Prostaglandin F2alpha is secreted in a pulsatile pattern from the uterus on days 14 to 16 after ovulation, which eliminates function of the CL

  16. Hormonal Profile of the Estrous Cycle

  17. Breeding Management Aids • Estrus (heat) detection • Transrectal palpation and ultrasonography • Hormonal treatment: • Estrus synchronization • Induction of ovulation

  18. Estrus Detection • Numerous techniques • Special considerations • Mare with foal at side • Young maiden mares

  19. Transrectal Palpation and Ultrasonography • Monitor follicular growth and development • Determine the optimal time for breeding • Identify ovarian and / or uterine abnormalities (ultrasonography)

  20. Fresh Semen • Goal is to deposit semen into the uterus within 48 hours prior to ovulation • Start breeding on the second day of heat, and breed every other day until the mare goes out of heat

  21. Fresh Semen (cont.) • Transrectal palpation and ultrasonography, and hCG or GnRH treatment can be used to more accurately time breeding and / or minimize the number of breedings per estrous cycle

  22. Insemination

  23. Shipped – Cooled Semen • Goal is to deposit semen into the uterus within 24 to 48 hours prior to ovulation • Examine mares with palpation and ultrasonography once daily while in heat

  24. Insemination

  25. Frozen Semen • Goal is to deposit semen into the uterus within 12 hours prior to ovulation or within 6 hours after ovulation • Examine mares with palpation and ultrasonography once daily for the first 2 or 3 days of heat, then increase frequency of examinations to 2 to 4 times per day when the follicle reaches preovulatory size

  26. Insemination • Thaw frozen semen following the directions provided by the person who froze the semen • Various types of packaging systems: • 0.5 cc straws, 2.5 or 5.0 cc straws (macrotubes), others • What constitutes an insemination dose?

  27. Pregnancy Examination Day 12 Day 35

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