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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

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

female reproductive physiology

Hypothalamus

GnRH

Pituitary Gland

LH

FSH

Ovaries

Progesterone

Estrogen

Female Reproductive Physiology
slide3

Hypothalamus

GnRH

Pituitary Gland

LH

FSH

Ovaries

Progesterone

Estrogen

reproductive seasonality
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
reproductive seasonality1
Reproductive Seasonality

Adapted from Ginther, 1974

photoperiod effect
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
physiological non breeding season winter anestrus anovulatory season
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)
transitional period
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
transitional period1
Transitional Period
  • 1 to 3 “waves” of follicular growth and regression
  • Irregular or prolonged estrus
  • Enlarged ovaries with multiple “clustered” follicles
physiological breeding season
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
follicular dynamics
Follicular Dynamics
  • 1 to 2 waves of follicles emerge during each estrous cycle
  • Each wave consists of a dominant follicle and several subordinate follicles
ovulation
Ovulation
  • LH surge induces final maturation of the follicle and ovulation
  • The ovulated follicle then develops into a corpus luetum (CL)
corpus luteum cl function
Corpus Luteum (CL) Function
  • The primary function of the CL is the secretion of progesterone, which is necessary for the maintenance of pregnancy
corpus luteum regression
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
breeding management aids
Breeding Management Aids
  • Estrus (heat) detection
  • Transrectal palpation and ultrasonography
  • Hormonal treatment:
    • Estrus synchronization
    • Induction of ovulation
estrus detection
Estrus Detection
  • Numerous techniques
  • Special considerations
    • Mare with foal at side
    • Young maiden mares
transrectal palpation and ultrasonography
Transrectal Palpation and Ultrasonography
  • Monitor follicular growth and development
  • Determine the optimal time for breeding
  • Identify ovarian and / or uterine abnormalities (ultrasonography)
fresh semen
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
fresh semen cont
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
shipped cooled semen
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
frozen semen
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
insemination2
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?