Editing Horse breeding (section)

=== Hormones involved in the estrous cycle, during foaling, and after birth ===
The cycle is controlled by several hormones which regulate the estrous cycle, the mare's behavior, and the reproductive system of the mare. The cycle begins when the increased day length causes the [[pineal gland]] to reduce the levels of [[melatonin]], thereby allowing the [[hypothalamus]] to secrete GnRH.
* '''GnRH ([[Gonadotropin releasing hormone]])''': secreted by the hypothalamus, causes the pituitary to release two gonadotrophins: LH and FSH.
* '''LH ([[Luteinizing hormone]])''': levels are highest 2 days following ovulation, then slowly decrease over 4–5 days, dipping to their lowest levels 5–16 days after ovulation. Stimulates maturation of the follicle, which then in turn secretes estrogen. Unlike most mammals, the mare does not have an increase of LH right before ovulation.
* '''FSH ([[Follicle-stimulating hormone]])''': secreted by the pituitary, causes the ovarian follicle to develop. Levels of FSH rise slightly at the end of estrus, but have their highest peak about 10 days before the next ovulation. FSH is inhibited by inhibin (see below), at the same time LH and estrogen levels rise, which prevents immature follicles from continuing their growth. Mares may however have multiple FSH waves during a single estrous cycle, and diestrus follicles resulting from a diestrus FSH wave are not uncommon, particularly in the height of the natural breeding season.
* '''[[Estrogen]]''': secreted by the developing follicle, it causes the pituitary gland to secrete more LH (therefore, these 2 hormones are in a positive feedback loop). Additionally, it causes behavioral changes in the mare, making her more receptive toward the stallion, and causes physical changes in the cervix, uterus, and vagina to prepare the mare for conception (see above). Estrogen peaks 1–2 days before ovulation, and decreases within 2 days following ovulation.
* '''[[Inhibin]]''': secreted by the developed follicle right before ovulation, "turns off" FSH, which is no longer needed now that the follicle is larger.
* '''[[Progesterone]]''': prevents conception and decreases sexual receptibility of the mare to the stallion. Progesterone is therefore lowest during the estrus phase, and increases during diestrus. It decreases 12–15 days after ovulation, when the [[corpus luteum]] begins to decrease in size.
* '''[[Prostaglandin]]''': secreted by the endrometrium 13–15 days following ovulation, causes luteolysis and prevents the corpus luteum from secreting progesterone
* '''eCG – [[equine chorionic gonadotropin]] – also called PMSG (pregnant mare serum gonadotropin)''': chorionic gonadotropins secreted if the mare conceives. First secreted by the endometrial cups around the 36th day of gestation, peaking around day 60, and decreasing after about 120 days of gestation. Also help to stimulate the growth of the fetal gonads.
* '''[[Prolactin]]''': stimulates lactation
* '''[[Oxytocin]]''': stimulates the uterus to contract