| | In this section, the hormones involved in the regulation of reproductive function in female cattle are presented.
| Hormone | Production Site | Function |
Gonadotropin-releasing
hormone (GnRH) | Hypothalamus |
- Stimulates the release of both LH and FSH from
the pituitary gland.
|
| Luteinizing hormone (LH) | Anterior pituitary |
- In conjunction with FSH and estrogen, causes
final development of the follicle destined to ovulate.
- The massive release of LH at the onset of estrus
causes ovulation of mature follicles.
- Stimulates progesterone secretion by the corpus luteum.
|
Follicle stimulating
hormone (FSH) | Anterior pituitary
preovulatory stage |
- Stimulates growth of antral follicles to the preovulatory stage.
- Stimulates estrogen production by granulosa cells
in maturing follicles.
- In conjunction with estrogen, induces LH receptors
in granulosa cells in follicles destined to ovulate.
- Secondary FSH surge after estrus may recruit
small follicles into the growing phase.
|
| Oxytocin | Hypothalamus
(stored in the posteriorpituitary)
and specific cells
of the corpus luteum |
- Stimulates milk let-down
- Causes smooth muscle contractions in the
reproductive tract to aid in sperm ovum transport
and expulsion of the fetus and fetal membranes.
- May be involved in luteal function and/or regression.
|
| Estrogen | Granulosa cells |
- Acts on the hypothalamus to cause estrous
behavior.
- In conjunction with FSH, induces LH receptor
formation on granulosa cells of follicles destined to ovulate.
- The marked rise in estrogen occurring just before
estrus causes the gonadotropin (LH and FSH) surge which culminates in ovulation.
- Stimulates uterine secretions, and activity of ciliated and smooth muscle
cells along the reproductive tract to aid in ovum and sperm
transport during estrus.
- Promotes growth of the mammary duct system.
|
| Progesterone | Corpus luteum (ovary) |
- Depresses the frequency of gonadotropin (LH and FSH) release to prevent ovulation.
- Stimulates uterine milk secretions to aid in nourishment of pre-implantation embryos.
- Depresses smooth muscle activity in the reproductive tract.
- Required for normal implantation and maintenance of pregnancy.
- Required for the development of the clusters of
milk-secreting alveoli on the mammary ducts.
|
| Relaxin | Corpus luteum (ovary) |
- At the end of pregnancy, stimulates ripening and
opening of the cervix and relaxation of the pelvic ligaments.
- Function during the estrous cycle is unknown.
|
| lnhibin | Ovarian follicles |
- Suppresses release of FSH from the pituitary.
- May be involved in the selection of the follicle destined to ovulate.
|
| Prostaglandin | Uterus
(plus most other body tissues) |
- Prostaglandin of the F series are involved in
regression of the corpus luteum in the absence of a viable embryo in the uterus.
- Prostaglandin of the E series appear to be involved with maintenance of the corpus luteum, and may be involved in the process of ovulation.
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Hormones are messengers. They are produced and secreted by one part of the body and travel, usually through the bloodstream, to another part of the body to stimulate or depress a particular function. Hormones are the means by which distant parts of the body communicate with each other. Communication disturbances disrupt reproductive function. In the past few years, researchers have discovered that the reproductive hormones are secreted in distinct pulses, a pattern (or code) which varies with the stage of the reproductive cycle. The target tissue, whether it is the ovary, uterus, pituitary or hypothalamus, responds only to specific pattern of hormone secretion that it recognizes. lf the target tissue is unable to recognize the pattern, either due to lack of receptors for the hormone messenger on the target tissue or due to an inappropriate pattern of hormone message, the programmed response does not occur.
Adapted from Beef Herd Management Reference Binder and Study Guide 404-1 |
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