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

Hypothalamus GnRH Pituitary Gland LH Ovaries FSH Progesterone Estrogen

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 Seasonality Adapted from Ginther, 1974

Reproductive seasonality is regulated primarily by changes in day length

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

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

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

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 F 2alpha is secreted in a pulsatile pattern from the uterus on days 14 to 16 after ovulation, which eliminates function of the CL

Hormonal Profile of the Estrous Cycle

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

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

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

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.) • 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

Insemination

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

Insemination

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

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?

Pregnancy Examination Day 12 Day 35