MARE REPRODUCTIVE

PHYSIOLOGY

ORGANS The following organs make up the

mare’s reproductive tract2 Ovaries2 Fallopian TubesUterusCervixVagina Vulva

Mammary glands are accessory organs

VULVA Exterior opening to reproductive canal Consists of:

Labia Clitoris Vestibule

Pneumovagina (windsucking) Poor conformation Vulva collects feces Air and debris can be sucked into the

reproductive tract Can be inherited Can be sealed with a caslick (episolasty)

CASLICK

VAGINA 6 to 8 inch long muscular, mucous

membrance – lined tube which connects the vestibule of the vulva to the cervix

Can change in color and vascularity due to hormonal changes during a mare’s estrous cycle

CERVIX Acts as a barrier between the vagina

and uterus During a point of estrus it will become

flaccid allowing the passage of semen and breeding instruments

UTERUS Multilayer, hollow, Y-shaped organ with

a uterine body and 2 branches (Horns) Suspended in the body by 2 ligaments

called broad ligaments Myometrium

Muscular tissue Provides contractions that expel foal during

birth Endometrium

Innermost layerContaining a rich blood supply and many

glands

OVIDUCTS AKA Fallopian Tubes Connects the tip of the uterine horn with

an ovary Infundibulum

Ovarian end of the oviduct Enlarged and shaped like a catchers mitt

with finger-like projections called fimbriae Fertilization of the ovum occurs here Isthmus

Final portion of the oviducts Narrows and joins the uterus

OVARY Both unique in shape and makeup Kidney bean shaped Ovulation Fossa

Concave side of the ovary Follicles 35 millimeters or larger are

considered capable of ovulating Corpus Luteum

Forms after the follicle has rupturedSecretes progesterone

TERMINOLOGY Estrous

Cycle Estrus

Actual Heat Anestrous

Not cyclingWinter Seasons

SEASONAL POLYESTRUS Reproductive seasons

Spring & SummerSeries of estrous cycles

Estrous Cycle21-23 days

Since it only happens in certain months they are considered seasonal polyestrus

BEHAVIOR Estrus

Actual Heat5-7 DaysCharacterized by receptivity to stallion

Diestrus14-16 daysMare will reject stallion

Bite or kick

ESTRUS BEHAVIOR

ENDOCRINOLOGY Endocrinology

Study of hormones Hypothalamus

Controls ovaries, oviducts, and uterusLocated in the mid-brain

Environmental CuesStart the reproductive season with a release

of the hormone GnRH Gonadotrophic Releasing Hormone

Released by the hypothalamus Stimulates the pituitary gland

Located at the base of the brain

ENDOCRINOLOGY In response to GnRH, the pituitary

releases to gonadotrophic hormonesFollicle Stimulating Hormone

Stimulates follicle growthLuteinizing Hormone

Stimulates ovaries When follicles reach approx 20-25 mm

in diameterSecrete Estradiol

Specific form of estrogen Peak immediately prior to ovulation

ENDOCRINOLOGY High concentrations of estradiol

stimulate the release of LH Stimulating ovulationSupport the initial stages of the corpus

luteum (CL) development Ovulation occurs at the end of estrus

Follicles undergo rapid conversion to form a CL

Luteal cells with the CL secrete progesterone

ENDOCRINOLOGY Progesterone

Inhibits the release of LH Changes mare behavior to diestrus If mare does not conceive, production is

halted Accomplished through the action of

prostaglandin F2 (PGF2)Released by the uterus 14-16 days after

ovulationCauses destruction of CL

Luteolysis