Mare Reproduction
Female Reproductive AnatomyThe female genitalia lie in the pelvic cavity consist of: Ovary. Oviduct. Uterus. Cervix. Vagina. Vulva.
Female Reproductive Anatomy
Female Reproductive AnatomyFemale Reproductive Anatomy
OvariesReproductive Seasonality
Physiological breeding seasonOvulatory seasonApril through SeptemberPhysiological non – breeding seasonAnovulatory season (anestrus)December and JanuaryTransitional periodSpring: February and MarchFall: October and NovemberReproductive Seasonality
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 24-48 hours before the end of oestrus.
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).
If a stallion nears, she may lean into him. Most mares cease estrous behavior within 24 to 48 hours following ovulation.
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
Influence of the length of day light on the ovary function in mares
Photoreceptors in the eyesPineal
Hypothalamus
Anterior pituitary
Ovaries
increasing day light
decreasing day light
neurotransmission
portal system
blood circulation
Melatonin
Melatonin
GnRH
GnRH
Gonadotropine
Gonadotropine
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 occurs1 to 3 “waves” of follicular growth and regressionIrregular or prolonged estrusEnlarged ovaries with multiple “clustered” follicles Transitional Period