Title: Reproductive System of the Horse
Course: APSC 451
Department: Equine Production
Mare’s Reproductive System: Lies horizontally in abdominal and pelvic cavities, consists of the following components:
Vulva
Vagina
Cervix
Ovaries
Oviduct
Uterus
Diagram of Mare's Reproductive System:
Vagina
Cervix
Horn of Vulva
Vestibule
Bladder
Body of Uterus
Uterus
Ovary
Fallopian Tube
Vulva:
External opening of the female reproductive tract.
Vagina:
A muscular tube (6-8 inches) lined with mucus membranes.
Connects the vulva to the cervix.
Elastic tissues accommodate stallion’s penis and foaling.
Cervix:
Provides entrance to the uterus, approximately 4 inches long.
Flaccid and open during estrus to facilitate semen passage.
Closed when the mare is not in estrus, serving as a barrier.
Ovary:
Primary reproductive organ, two located at the upper end.
Contains all egg cells a mare will produce in her lifetime; each egg is contained in a follicle.
Oviducts (Fallopian Tubes):
Site of fertilization.
Egg is discharged when the follicle ruptures, trapped by the infundibulum.
Oviduct carries fertilized egg to the uterus.
Uterus:
Largest female reproductive organ, responds as fetus grows.
Multi-layered, hollow, Y-shaped structure.
Two branches (horns) and a base (uterine body).
Parts of Uterus:
Uterine body
Uterine horn
Oviduct
Infundibulum
Ovary
Broad ligament
Cervix
Vagina
Vulva
Uterus Structure:
Three distinct layers:
Serous Layer: Outer layer.
Myometrium: Middle layer with muscular tissue for parturition.
Endometrium: Innermost layer with rich blood supply.
Estrous Cycle:
Normal cycle lasts 21-22 days:
Estrus Phase: Mare receptive to stallion, lasts 6-8 days.
Diestrus Phase: Mare not in heat, rejects stallion, lasts 14-15 days.
Cyclic Behavior:
Primary factor: increased hours of light.
Artificial lighting can regulate cycles.
Hormones control cycle.
Hormonal Control:
Increased light stimulates hypothalamus to produce GnRH.
GnRH leads to pituitary secretion of FSH and LH.
Follicle Development:
FSH stimulates ovaries to develop follicles.
Developing follicle secretes estrogen, stimulating sexual activity.
High estrogen triggers LH release from pituitary.
Ovulation:
LH causes follicle to rupture, releasing the ovum.
After ovulation, estrogen levels drop; corpus hemorrhagicum forms from the ruptured follicle.
Corpus luteum formed from luteinization of the hemorrhagicum.
Progesterone Function:
Produced by granulosa cells in the corpus luteum.
Shuts down LH release, maintains pregnancy.
Cervix closes; mare loses interest in stallion.
Cyclic Reset:
If mare does not conceive, progesterone influences uterus for 12-14 days.
Uterine endometrium secretes prostaglandin, causing corpus luteum regression.
FSH levels rise, restarting the cycle.
Pregnancy Recognition:
If conception occurs, embryo migration inhibits prostaglandin secretion.
Corpus luteum remains functional, maintaining progesterone levels for pregnancy.
Hormonal Pathway:
Diagram showing relationship between sunlight hours, pineal gland stimulation, hypothalamus, GnRH, pituitary hormones (FSH, LH), ovarian hormones, and roles in reproduction. Gondotropin Releasing Hormone
Breeding Behavior:
Mares are seasonally polyestrous, cycling several times/year.
Cycling begins in January-February; peaks in June-July.
Seasonal Cycling:
Cycling irregular by September-October; ceases in November (anestrous).
Estrous Cycle Initiation:
Begins at puberty (15-24 months), normal cycle is 21-22 days.
Fertilization:
Ovum viable for 8-12 hours post-ovulation.
Sperm can survive 24-48 hours in oviduct; takes 4-6 hours to reach ovum.
Embryo Development:
Fertilized egg travels to uterus in 5-6 days.
By days 16-18, the embryo implants in one horn.
Gestation Period:
Average gestation length: 335 days (+/- 2-4 weeks).
Influenced by season, nutrition, and the fetus' sex.
Stallion’s Reproductive System:
Main functions: produce sperm and testosterone, introduce sperm into mare.
Stallion's Anatomy:
Includes the prostate, vesicular glands, bladder, vas deferens, urethra, glans penis, scrotum, testicles, and epididymis.
Components of Male Reproductive System:
Two testes, accessory sex glands, tubules for sperm transport, and scrotum.
Detailed Male Anatomy:
Vesicular glands, prostate, ampulla, deferent duct, epididymis, bulbourethral glands, glans penis, and retractor penis muscle.
Testes Characteristics:
Two testes suspended by spermatic cord, ovoid shape (80-140 mm long, 56-80 mm wide).
Housed in scrotum, separated by a septum.
Testicular Descent:
Testes should descend into scrotum by 3 weeks gestation or 2 weeks post-birth.
If not, it results in cryptorchidism.
Penis Structure:
Organ of copulation, consisting of three parts: root, body (shaft), and glans penis (enlarged end).
Sperm Production:
Occurs in seminiferous tubules of testes, billions produced daily.
Epididymis Function:
Transports, matures, and stores sperm from testes.
Deferent ducts transport sperm to accessory glands, adding fluids to semen.
Leydig Cells:
Produce testosterone, present in interstitial tissues of seminiferous tubules.
FSH and LH also involved in stallion's reproductive processes.
Mating Process:
Involves three basic processes: erection, emission, and ejaculation.
Sperm Maturity:
Full production begins at over a year old, reaches capacity at about 4 years; remains constant until age 20.
Factors Influencing Sperm Production:
Season, testicular size, age, frequency of ejaculation.
Seasonality in Stallions:
Stallions are seasonal breeders, sperm production year-round.
Best months for testicular size: May, June, July.
Sperm Count Variation:
Sperm count drops significantly in December-January compared to June-July.
Stallions should be exposed to 16 hours of light daily to optimize breeding conditions.