The Reproductive System of a MareLivestock Production, Equine Science, Advanced Animal Science

Introduction to the Estrous Cycle•The recurring reproductive cycle in many

female mammals, including estrus, ovulation, and changes in the uterine lining.

•Differs from the menstrual cycle in that the endometrium is not shed

•Generally, species with estrous cycles are not sexually active when they are not in the estrus phase of their cycle

The Estrous Cycle

• Estrus (Follicular) – period when mare is sexually receptive to stallion, the “heat” stage

• Diestrus (Luteal) – period when mare is not sexually receptive

The Estrous Cycle (cont.)• Helps the mare

physically prepare for conception

• Generally, the cycles occur between spring and fall (when the days are longer)

• 18 - 21 days long

Terminology•Anestrus – complete absence of estrus,

prevents mares from conceiving during the winter months

•Seasonally polyestrus – mares go through regular estrus cycles during part of the year

The Parts

•Vulva – the external opening of the reproductive canal

•Vagina – 6-8 inch long muscular membrane connecting the vulva to cervix; tissues are elastic to accommodate penis during breeding and foal during birth

•Cervix – about 4 inches, elastic muscle, located behind vagina

• Uterus – contains 2 branches that are referred to as “horns”; protects and nourishes the embryo/fetus

• Oviducts –attached to each uterine horn; transports the discharged egg from the ovaries; the mare’s Fallopian tubes

• Ovaries – 2-3 inch bean-shaped organs; contains follicles that hold the mare’s egg cells

Reproductive Anatomy

During estrus…….• Vagina becomes

relaxed and secretions increase

• Vulva relaxes• Cervix increases

secretions, opens, and relaxes

• Uterus becomes heavier, losing its tone, due to increased levels of estrogen

Signs of Estrus

•Frequent urination•“Squatting” posture•Winking of labia•Raising of tail•Receptive toward stallion•Discharge from vagina

Breeding Tips

•Have a vet examine the mare and stallion for diseases and evaluate the chances of conceiving

•Wash the mare’s (and stallion’s) genitals with warm non-soapy water to minimize the chances of dirt and bacteria entering during the mating process

•Wrap the upper 1/3 of mare’s tail with a clean wrap so that there is a smaller chance of it getting in the way

Breeding Methods

•Live Cover – methods in which mare and stallion are physically brought together to breed▫Hand Mating – most widely used; people

handle both mare and stallion▫Corral Mating – mare and stallion are turned

into a paddock where they mate naturally▫Pasture Mating – stallion is turned out with a

group of mares for the entire breeding season

Alternative Breeding Methods• Artificial

Insemination (AI) – mare is inseminated by a veterinarian

• Embryo Transfer – removing the embryo from a mare and transferring it to a surrogate mare

Artificial Insemination (AI)Pros Cons

• Semen sample from stallion can be used for more than one mare

• Frozen semen can be stored for long periods of time, making international breeding possible

• Chances of contamination in the mare is reduced

• Smaller chance of injury to both the stallion and mare

• Humans handle every step of this process, so there is a higher chance of human error

• Various competition organizations, such as The Jockey Club, does not allow competing horses to be bred through AI

Important Hormones• Estrogen –

▫ Secreted by follicles▫ Hormone that causes the

pituitary gland to secrete more LH

▫ Makes mare more receptive toward stallion

▫ Prepares mare for conception physically

▫ Peaks 1-2 days before ovulation

• Progesterone – ▫ Prevents conception and

decreases the receptiveness of the mare to the stallion

▫ Causes cervix to close▫ At its lowest level during

the estrus phase▫ Suppresses hormonal

activity to maintain pregnancy (if mare is pregnant)

▫ If mare is not pregnant, the estrous cycle will continue

More Hormones• Luteinizing hormone (LH)

– ▫ Secreted by the pituitary▫ Assists the maturation of

the follicle• Follicle stimulating

hormone (FSH) – ▫ Secreted by pituitary,

transported through bloodstream to ovaries

▫ Stimulates the production of follicles