1. Mare Reproduction

2. Female Reproductive Anatomy
The female genitalia lie in the pelvic cavity consist of:
Ovary.
Oviduct.
Uterus.
Cervix.
Vagina.
Vulva.

3. Female Reproductive Anatomy

4. Female Reproductive Anatomy

5. Female Reproductive Anatomy
Ovaries

6. 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

7. Reproductive Seasonality

8. The estrous cycle is under seasonal control, and daylight is the environmental signal for this regulation.
Mares are polyestrus during the breeding season.
During the reproductive season, mares will come into heat on average every 21 (18-24) days; ponies have a longer mean cycle (25 days).
The oestrus lasts for about 5 (3-9) days and ovulation takes place hours before the end of oestrus.

9. Estrus (heat) lasts an average of 5 to 7 days, the longest heat period of any domestic animal.
Estrus is characterized by receptivity to the stallion.
A mare showing classical estrous behavior will adopt a urination stance – squatting with legs spread apart and tail raised.
She will urinate small volumes frequently and expose her clitoris by everting her vulva (winking).

10. If a stallion nears, she may lean into him.
Most mares cease estrous behavior within 24 to 48 hours following ovulation.

12. 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

13. Influence of the length of day light on the ovary function in mares
Photoreceptors
in the eyes
increasing day light
Influence of the length of day light on the ovary function in mares
decreasing day light
neurotransmission
Pineal
Melatonin
Melatonin
Hypothalamus
portal system
GnRH
GnRH
Anterior
pituitary
blood circulation
Gonadotropine
Gonadotropine
Ovaries

14. Minimal follicular development
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)

15. 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

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

17. 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

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

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

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

21. 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