1. Anatomy of Reproduction of the Mare
By: Anthony Watson

3. Functions of the Mares’ Reproduction Tract
Ovary (gonads)- the female organ that produces the egg, mares have 2 of them. Its primary function is to produce female gametes (ova) and estrogen and progesterone. When the egg is ready to be released it is released into the infundibulum. The infundibulum is a funnel-like membrane that surrounds the ovary, and serves kind of like a net when the (newly ovulated oocyte) egg is released. The oviduct (fallopian tube) then carries the egg from the ovary to the uterus after it has been fertilized.

4. Functions of the Mares’ Reproduction Tract
The Uterus has several functions. Its first function is to serve as a passageway for sperm cells to enter the oviduct. Sperm can live in the oviduct for 2-3 days. Uterine contractions during copulation push the sperm to the oviduct. Sperm are allowed about 2-3 hours for entry, then sperm remaining in the uterus are expelled out of the cervix. Secondly, the uterus known as the womb is where the fetus develops.

5. Functions of the Mares’ Reproduction Tract
The cervix is a thick-walled organ that has many functions. During estrous the cervix becomes soft allowing semen to enter. It also produces mucus that flows toward the vagina of the mare that helps flush foreign material introduced during copulation, sometimes including sperm. Its last function is to form a barrier during pregnancy called the “cervical seal of pregnancy” which does not allow foreign material to enter the uterus during pregnancy.

6. Functions of the Mares’ Reproduction Tract
The last main organ of the mare is the vagina. The vagina serves as the copulatory organ were sperm is received, as well as the site for urine expulsion.

7. Estrous Cycle
Seasonally Polyestrus- reproductively active at a defined portion of the year, during which they cycle repeatedly. (Spring, Summer, and Fall) Anestrus during the winter months, meaning stop cycling.
Estrous Cycles are driven by hormonal changes.

8. Estrous Cycle Mares cycle is divided into 2 phases.
Estrus (Follicular Phase) – the receptive phase, where estrogen is dominant and releases the Luteinizing hormone (LH).
Diestrus (Luteal Phase) – non-receptive phase, progesterone is dominant and the Follicle Stimulating Hormone is released (FSH).
FSH and LH are called gonadotrophins because they are responsible for stimulating activity of certain structures in the mare’s ovaries (gonads)

9. Ovaries The ovaries are the organs of constant change.
Corpus Luteum (CL) – an orange to yellow colored transient endocrine structure formed after ovulation from ovarian follicle cells. It is responsible for producing progesterone and oxytocin.
Follicle – a blister-like structure on the ovary that encloses the “ripened” egg. Upon hormonal stipulation, the egg will release --- a process termed ovulation.

10. Estrous Cycle
Follicular Phase – the phase of the estrous cycle characterized by the presence of a dominant follicle that produces estradiol. Females display behavioral estrus and ovulate during the follicular phase.
Luteal Phase – the phase of the estrous cycle characterized by progesterone dominance and presence of a functional CL. The luteal phase begins immediately after ovulation and ends after lysis of the CL.
(See Diagram for the phases and days)