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

GnRH Hypothalamus Pituitary Gland Ovaries LHFSH Progesterone Estrogen Female Reproductive Physiology

GnRH Hypothalamus Pituitary Gland Ovaries LHFSH Progesterone Estrogen

Reproductive Seasonality Physiological breeding seasonPhysiological breeding season Ovulatory seasonOvulatory season April through SeptemberApril through September Physiological non – breeding seasonPhysiological non – breeding season Anovulatory season (anestrus)Anovulatory season (anestrus) December and JanuaryDecember and January Transitional periodTransitional period Spring: February and MarchSpring: February and March Fall: October and NovemberFall: 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 lengthReproductive activity in the spring is stimulated by increasing day length Mechanism involves alteration of hormone secretion by the pineal gland and hypothalamusMechanism involves alteration of hormone secretion by the pineal gland and hypothalamus Pineal gland: melatoninPineal gland: melatonin Hypothalamus: GnRHHypothalamus: GnRH Artificial lighting can be used to hasten the onset of the ovulatory seasonArtificial lighting can be used to hasten the onset of the ovulatory season

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

Transitional Period Increased day length stimulates GnRH secretion from the hypothalamusIncreased day length stimulates GnRH secretion from the hypothalamus GnRH stimulates FSH and LH secretionGnRH stimulates FSH and LH secretion FSH induces follicular developmentFSH induces follicular development Estrogen produced by developing follicles causes the mare to exhibit irregular and / or prolonged estrusEstrogen 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 occursWhen LH levels have increased, the first ovulation of the year occurs

Transitional Period 1 to 3 “waves” of follicular growth and regression1 to 3 “waves” of follicular growth and regression Irregular or prolonged estrusIrregular or prolonged estrus Enlarged ovaries with multiple “clustered” folliclesEnlarged ovaries with multiple “clustered” follicles

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

Follicular Dynamics 1 to 2 waves of follicles emerge during each estrous cycle1 to 2 waves of follicles emerge during each estrous cycle Each wave consists of a dominant follicle and several subordinate folliclesEach wave consists of a dominant follicle and several subordinate follicles

Ovulation LH surge induces final maturation of the follicle and ovulationLH surge induces final maturation of the follicle and ovulation The ovulated follicle then develops into a corpus luetum (CL)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 pregnancyThe 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 cycleNonpregnant 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 daysThe 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 CLProstaglandin 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) detectionEstrus (heat) detection Transrectal palpation and ultrasonographyTransrectal palpation and ultrasonography Hormonal treatment:Hormonal treatment: Estrus synchronizationEstrus synchronization Induction of ovulationInduction of ovulation

Estrus Detection Numerous techniquesNumerous techniques Special considerationsSpecial considerations Mare with foal at sideMare with foal at side Young maiden maresYoung maiden mares

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

Fresh Semen Goal is to deposit semen into the uterus within 48 hours prior to ovulationGoal 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 heatStart 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 cycleTransrectal 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 ovulationGoal 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 heatExamine 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 ovulationGoal 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 sizeExamine 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 semenThaw frozen semen following the directions provided by the person who froze the semen Various types of packaging systems:Various types of packaging systems: 0.5 cc straws, 2.5 or 5.0 cc straws (macrotubes), others0.5 cc straws, 2.5 or 5.0 cc straws (macrotubes), others What constitutes an insemination dose?What constitutes an insemination dose?

Pregnancy Examination Day 12 Day 35