The estrous cycle
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The estrous cycle refers to the physiological changes induced by reproductive hormones in female mammals. It begins at sexual maturity and is interrupted by pregnancy or anestrous phases. The cycle is regulated by hormones like GnRH, FSH, LH, estrogens and progesterone. In most species, the cycle involves the stages of proestrus, estrus, metestrus, and diestrus and results in ovulation about halfway through. The length and timing of the estrous cycle varies between species but generally allows females to be sexually receptive and able to conceive when environmental conditions favor survival of offspring.
The estrous cycle
- 2. Estrous Cycle…. also known as Oestrous cycle. derived from Latin oestrus and originally from Greek . comprises the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. start after puberty in sexually mature females. interrupted by anestrous phases or pregnancies. Typically estrous cycles continue until death. may display bloody vaginal discharge.
- 3. often mistaken for menstruation, also called a "period". sexually receptive (estrus) interrupted by periods in which the female is not fertile and sexually receptive (anestrus). regulatory hypothalamic system that releases gonadotropin releasing hormone (GnRH) in pulses, the pituitary that secretes follicle stimulating hormone (FSH) and luteinizing hormone (LH), and the ovary itself that releases sex hormones, including estrogens and progesterone.
- 4. Estrous cycle? menstrual cycle? In estrous cycles, reabsorbtion of the endometrium occur if conception does not occur during that cycle. Animals that have menstrual cycles shed the endometrium through menstruation instead. animal with estrous cycles, females are generally only sexually active during the estrus phase of their cycle. This is also referred to as being "in heat.“ females of species with menstrual cycles can be sexually active at any time in their cycle, even when they are not about to ovulate.
- 5. Some may undergo estrous only one time a year during a particular season. others may undergo a succession of cycles during a certain time of the year if they do not become pregnant. some may undergo cycles throughout the whole year. may be "induced ovulators," with cyclic receptivity but requiring mating in order to ovulate and undergo the luteal phase. some require specific stimuli such as physical contact to even come into behavioral estrus.
- 6. estrous cycle allows the animals to place most of their mating energy into particular periods. obvious to the males when females are in estrous. In some cases, estrus is limited to times that will allow birth when there are optimal environmental conditions for survival of the young. there are five stages in estrous cycle (Walter Heape, 1984). - Proestrus - Estrus ( on heat ) - Metestrus - Diestrus - Anestrus
- 7. Estrous cycle in cattle cows are Polyestrous (species that can go through a succession of estrous cycles during the year). undergo estrus several times a year if not pregnant. The entire estrous cycle averages 21 days long, but can be as short as 18 days and as long as 24 days. Cows sometimes exhibit a bloody vaginal discharge during estrus or metestrus; the bleeding originates from essentially intact uterine vessels (diapedesis or pseudomenstruation ).
- 8. cows undergo estrous cycle on four stages; proestrus, estrus, metestrus, and diestrus. Day 0 is considered to be estrus. Days 1-5 are metestrus. Days 6-17 are diestrus. Days 18-20 are proestrus.
- 10. During the late luteal phase and pregnancy recognition signal is not present by day 17-18, prostaglandin is released. casuses luteal regression, progesterone declines. the loss of progesterone inhibition, GnRH rises and causes stimulation of LH and FSH. FSH causes maturation of follicles past the antral stage. dominant follicle establishes itself and is the main follicle that grows. The growing follicle produces estrogen in the granulosa cells.
- 11. It is the estrogen that causes the signs of estrus in the cow. Estrogen actually peaks before heat (estrus) and causes the final LH release. Inhibin is also produced by the growing follicle and prevents other smaller follicles from growing. This inhibition assures selection of a single follicle to ovulate. estrogen causes progesterone receptor synthesis, which allows LH binding to luteal cells. Estrus lasts 18-20 hours, Ovulation occurs 12-18 hours after the end estrus.
- 12. Metestrus is 3-5 days long, corpus hemorrhagicum (CH), which is the 'bloody body' that formed from the follicle after ovulation, is developing into a corpus luteum. Diestrus lasts from days 5-17 . the time that the mature corpus luteum is producing progesterone. During diestrus there are 2, 3 or 4 waves of follicular growth and are very important in understanding a cow's response to estrous cycle synchronization.
- 14. The usual length of oestrus is 14 to 15 hours. Some cows may have a silent heat as their first heat when they start cycling. will not mount, nor tolerate attempts to be mounted. may have smelt pheremones, and may search for them (smelling, or licking in the under the tail region of another cow, or may sample urine from a cow). may rest her chin on the tail-spinal area of a cow in front of her. If the cow straightens her spine, the behind cow may mount (the front cow is on standing heat). vulva may appear swollen and reddish.
- 16. In a group of on heat cows you'll observe mounting behaviour, attempting to mount, some head to head mounting, quite a bit of urine sampling, some allogrooming, chins resting on the tail head, and flehman. A string of clear mucus may be visible from the vulva. The skin over any bony areas near her tail can be completely rubbed off.
- 17. Straightening her back is an indication that she is in standing heat. The sight of a bull may "kick start" some cows into the hormonal changes essential for oestrus.
- 18. Estrous cycle in swine swine ( sow ) is also Polyestrous animal. Estrus frequencies are 21 days. estrus (heat) usually lasting 24 to 72 hours. first day that heat is observed is usually designated as day 0. Ovulation normally occurs toward the end of estrus, at which time the follicles release their ova (eggs). The cells that remain form the copora lutea, the endocrine gland that secretes progesterone.
- 19. Natural progesterone concentrations increase about 24 hours after ovulation and plateau between days 6 and 10. If developing embryos are not present in the uterus at days 12 to 14, progesterone levels begin to decrease rapidly. By day 16, progesterone levels can be nearly undetectable. A surge in secretion of FSH (follicle-stimulating hormone) and LH (luteinizing hormone), in turn, stimulates the growth of new follicles, which ultimately results in estrus and ovulation.
- 22. Estrous cycle in Sheep Seasonally polyestrous animals . can go through a success of estrous cycles during a particular time of the year. go into estrus more than one time during a particular season if not mated. Short-day breeders, sexually active in fall or winter.
- 23. Spontaneous ovulators. do not require an act of coitus to induce follicle rupture by rather a series of hormonal events result in the occurrence of ovulation (ovarian steroids induce a pattern of GnRH release that stimulates a preovulatory LH surge). odour from bucks and rams will start oestrus in the females. length of daylight hours that trigger the start of mating. estrous occurs at 15 - 24 day intervals, on breeding season. The on heat stage can range from 8 hours to 60 hours.
- 24. show very few "on heat" signs. She'll mount other does. She'll allow other does to mount her. She will call out, She will wag her tail sideways. urinate frequently, leaving small quantities of her pheremones (in the urine) in lots of places. mucus vaginal discharge. "bottom" is swollen, and pinkish. not eating as much as usual. 1 or 2 ova are often shed at ovulation, Improved nutrition has been known to increase the ovulation rate.
- 25. 17 day estrous cycle. Most ewe lambs reach puberty between 5 and 12 months of age. length of the estrus cycle ranges from 13 to 19 days and averages 17 days. phases of the estrous cycle are proestrus, estrus, metestrus, and diestrus. Estrus is the period of time when the ewe is receptive to the ram and will stand for mating. It lasts approximately 24 to 36 hours. Ovulation occurs in mid to late-estrus. Metaestrus begins with the cessation of estrus and lasts for about 3 days.
- 26. it is the period of the formation of corpus luteum . corpus luteum produces progesterone and maintains pregnancy in the ewe. Diestrus is the period of the estrus cycle when the CL is fully functional. Estrous cycles are usually affected by the seasons.
- 27. Estrous cycle in goat Dairy goats are usually seasonal breeders. has an 18-21 day estrus cycle or "season." doe's "season" lasts from a few hours to two or three days. day zero, the doe begins to exhibit behavioral signs of estrus: tail flagging, mounting other does, urinating more often, and she will be more vocal than usual. Day two brings vaginal estrus, and the doe may still be exhibiting behavioral signs.
- 28. In response to estrogen-induced discharge of the luteinizing hormone (LH), ovulation occurs on day three. Metestrus starts with ovulation and continues until day six. theca and granulosa cells differentiate into luteal cells under the influence of LH, forming the corpus luteum. day four, the CL begins to secrete progesterone. Between days seven and fourteen, the CL reaches its maximum size and functionality. the oxytocin receptor OTR is expressed on day On days thirteen and fourteen.
- 29. OTR responsible on the release of oxytocin (OT) and prostaglandin F2a (PGF). Proestrus begins about day fifteen. OT levels increase, which corresponds with the pulsatile release of PGF. presence of PGF and OT begin to break down the CL. CL is almost completely reabsorbed by day seventeen.. Estrogen present from days fifteen to seventeen regulates the pulses of OT and PGF to assure complete luteolysis. From days eighteen to twenty-one, a period known as diestrus, progesterone loses its ability to suppress the endometrial expression of the estrogen receptor and OTR, and thus the cycle begins again.
- 31. Prepared by; Leo Benn