AVS 222

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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

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

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Reproductive Seasonality
Adapted from Ginther, 1974
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Reproductive seasonality is regulated
primarily by changes in day length
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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

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Physiological Non Breeding Season(Winter
Anestrus / Anovulatory Season)

• Minimal follicular development
• GnRH, FSH and LH secretion are low
• small, firm ovaries
• Follicles lt 15 mm in diameter
• Mares may exhibit estrous behavior (heat)

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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

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Transitional Period

• 1 to 3 waves of follicular growth and
  regression
• Irregular or prolonged estrus
• Enlarged ovaries with multiple clustered
  follicles

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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

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Follicular Dynamics

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

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Ovulation

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

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Corpus Luteum (CL) Function

• The primary function of the CL is the
  secretion of progesterone, which is
  necessary for the maintenance of pregnancy

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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

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Hormonal Profile of the Estrous Cycle
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Breeding Management Aids

• Estrus (heat) detection
• Transrectal palpation and ultrasonography
• Hormonal treatment
• Estrus synchronization
• Induction of ovulation

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Estrus Detection

• Numerous techniques
• Special considerations
• Mare with foal at side
• Young maiden mares

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Transrectal Palpation and Ultrasonography

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

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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

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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

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Insemination
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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

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Insemination
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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

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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?

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Pregnancy Examination
Day 12
Day 35
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