Lets take a look at Doe's Reproductive Physiology....

The primary messengers which allow all of the organs involved in reproduction to communicate and coordinate are "hormones". Hormones are protein molecules that are produced by many organs and structures in the body, usually in response to an external stimulus (such as light or smell). Reproductive hormones rise and fall at appropriate times (cycles) to ensure the female behaviorally accepts the male (is standing heat) when ovulation is about to occur, and to ensure the uterus is ready to accept and nourish the fertilized egg. Hormones also "feedback" and decrease some reproductive functions when it is appropriate, so that the ovaries do not produce and ovulate eggs needlessly when an animal is pregnant. In animals which breed only during certain seasons of the year, these hormal reproductive cycles are turned on and off accordingly.

The hypothalamus is a gland located on the ventral (bottom) surface of the brain. The hypothalamus produces several hormones that are important in regulation of various body functions, including reproduction. The primary reproductive hormone produced by the hypothalamus is "Gonadotropin-Releasing Hormone (GNRH). GNRH is produced in response to daylight length (photoperiod) in animals that have a seasonal reproductive pattern. In deer, as the days get shorter and the length of daylight per day decreases, GNRH production in the hypothalamus increases, and levels of GNRH rise in the bloodstream.

The anterior pituitary gland is located in close proximity to the hypothalamus. Rising levels of GNRH stimulate the anterior pituitary gland to produce and release two hormones: Follicle Stimulating Hormone (FSH) and Leutinizing Hormone (LH). FSH stimulates the development of egg containing follicles on the ovary. LH promotes ovulation of these follicles and initiates the development of the corpus luteum after ovulation. Stimulation of the follicle by FSH is required before LH can be effective and cause a follicle to ovulate.

The ovary produces two reproductive hormones: Estrogen and Progesterone. As a follicle develops in the ovary, it secretes Estrogen. The primary function of Estrogen is to cause the behavioral signs of heat (estrus) or receptivity to the male. Once a follicle ovulates, the remains of the follicle wall develop into a Corpus Luteum, which then secretes Progesterone. The primary function of progesterone is to prepare the uterus for implantation of the fertilized egg. The Corpus Luteum must be stimulated by Estrogen before it can produce Progesterone. Because it would be wasteful for an animal, which has already ovulated and bred, to continue to produce follicles or to ovulate, rising estrogen levels inhibit the production of follicle stimulating hormone (FSH) and luetinizing hormone (LH), preventing both. Progesterone, produced by the corpus luteum during pregnancy, also inhibits follicle stimulating hormone (FSH) and the development of follicles.

Now, does anybody want to know how this can helps us a hunter?