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Estrous cycle

(Redirected fromPolyestrous)
For the biological genus name of the gadfly, seeOestrus (fly).For Satyr leader, seeOestrus (mythology).

Theestrous cycle(fromLatinoestrus'frenzy', originally fromAncient Greekοἶστρος(oîstros)'gadfly') is a set of recurring physiological changes induced byreproductive hormonesinfemalesofmammaliansubclassTheria.[1]Estrous cycles start aftersexual maturityin females and are interrupted by anestrous phases, otherwise known as "rest" phases, or bypregnancies.Typically, estrous cycles repeat until death. These cycles are widely variable in duration and frequency depending on the species.[2]Some animals may display bloody vaginal discharge, often mistaken formenstruation.[3]Many mammals used in commercial agriculture, such as cattle and sheep, may have their estrous cycles artificially controlled with hormonal medications for optimum productivity.[4][5]The male equivalent, seen primarily in ruminants, is calledrut.[2]

Differences from the menstrual cycle

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Further information:Menstrual cycle § Cycles and phases

Mammals share the same reproductive system, including the regulatoryhypothalamicsystem that producesgonadotropin-releasing hormonein pulses, thepituitary glandthat secretesfollicle-stimulating hormoneandluteinizing hormone,and the ovary itself that releasessex hormones,includingestrogensandprogesterone.

However, animals that have estrous cyclesresorbtheendometriumif conception does not occur during that cycle. Mammals that have menstrual cycles shed the endometrium throughmenstruationinstead.

Humans,elephant shrews,and a few other species havemenstrual cyclesrather than estrous cycles. Humans, unlike most other species, haveconcealed ovulation,a lack of obvious external signs to signal estral receptivity atovulation(i.e., the ability to become pregnant). Some species of animals with estrous cycles have unmistakable outward displays of receptivity, ranging from engorged and colorfulgenitalsto behavioral changes likemating calls.

Etymology and nomenclature

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Estrusis derived via Latinoestrus('frenzy', 'gadfly'), from Greekοἶστροςoîstros(literally 'gadfly', more figuratively 'frenzy', 'madness', among other meanings like 'breeze'). Specifically, this refers to the gadfly inAncient Greek mythologythatHerasent to tormentIo,who had been won in herheiferform byZeus.[citation needed]Euripidesusedoestrusto indicate 'frenzy', and to describe madness.Homerused the word to describe panic.[6]Platoalso used it to refer to an irrational drive[7]and to describe thesoul"driven and drawn by the gadfly of desire".[8]Somewhat more closely aligned to current meaning and usage ofestrus,Herodotus(Histories,ch. 93.1) usesoîstrosto describe the desire of fish tospawn.[9]

The earliest use in English was with a meaning of 'frenzied passion'. In 1900, it was first used to describe 'rutin animals; heat'.[10][11]

InBritish English,the spelling isoestrusor (rarely)œstrus.In all English spellings, the noun ends in-usand the adjective in-ous.Thus inModern International English,a mammal may be described as "in estrus" when it is in that particularpart of the estrous-cycle.

Four phases

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"Estrus" redirects here. For other uses, seeEstrus (disambiguation).

A four-phase terminology is used in reference to animals with estrous cycles.

Proestrus

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One or severalfolliclesof theovarystart to grow. Their number is species-specific. Typically, this phase can last as little as one day or as long as three weeks, depending on the species. Under the influence of estrogen, the lining of the uterus (endometrium) starts to develop. Some animals may experience vaginal secretions that could be bloody. The female is not yet sexually receptive; the oldcorpus luteumdegenerates; the uterus and the vagina distend and fill with fluid, become contractile and secrete a sanguinous fluid; thevaginal epitheliumproliferates and the vaginal cytology shows a large number of non-cornified nucleated epithelial cells. Variant terms forproestrusincludepro-oestrus,proestrum,andpro-oestrum.

Estrus

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Estrusoroestrusrefers to the phase when the female is sexually receptive ( "in heat"in American English, or"on heat"in British English). Under regulation bygonadotropic hormones,ovarian folliclesmature and estrogen secretions exert their biggest influence. The female then exhibits sexually receptive behavior,[12]a situation that may be signaled by visible physiologic changes. Estrus is commonly seen in the mammalian species, including some primates.

In some species, thevulvabecomes swollen and reddened.[13]Ovulationmay occur spontaneously in others. Especially amongquadrupeds,a signal trait of estrus is thelordosis reflex,in which the animal spontaneously elevates her hindquarters.

Controlled internal drug releasedevices are used inlivestockfor the synchronization of estrus.

Metestrus or diestrus

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This phase is characterized by the activity of thecorpus luteum,which produces progesterone. The signs of estrogen stimulation subside and thecorpus luteumstarts to form. Theuterinelining begins to appear. In the absence ofpregnancy,the diestrus phase (also termedpseudopregnancy) terminates with theregressionof the corpus luteum. The lining in the uterus is not shed, but is reorganized for the next cycle. Other spellings includemetoestrus,metestrum,metoestrum,dioestrus,diestrum,anddioestrum.

Anestrus

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Anestrus refers to the phase when the sexual cycle rests. This is typically a seasonal event and controlled by light exposure through thepineal glandthat releasesmelatonin.Melatonin may repress stimulation of reproduction in long-day breeders and stimulate reproduction in short-day breeders. Melatonin is thought to act by regulating thehypothalamicpulse activity of thegonadotropin-releasing hormone.Anestrus is induced by time of year,pregnancy,lactation,significantillness,chronic energy deficit, and possibly age. Chronic exposure to anabolic steroids may also induce a persistent anestrus due to negative feedback on the hypothalamus/pituitary/gonadal axis. Other spellings includeanoestrus,anestrum,andanoestrum.

After completion (or abortion) of a pregnancy, some species havepostpartum estrus,which is ovulation and corpus luteum production that occurs immediately following the birth of the young.[14]For example, themousehas a fertile postpartum estrus that occurs 14 to 24 hours following parturition.

Cycle-variability

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Estrous cycle variability differs among species, but cycles are typically more frequent in smaller animals. Even within species significant variability can be observed, thuscatsmay undergo an estrous cycle of 3 to 7 weeks.[15]Domestication can affect estrous cycles due to changes in the environment. For most species, vaginal smearcytologymay be used in order to identify estrous cycle phases and durations.[16]

Frequency

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Some species, such ascats,cowsanddomestic pigs,arepolyestrous,meaning that they can go into heat several times per year. Seasonally polyestrous animals orseasonal breedershave more than one estrous cycle during a specific time of the year and can be divided into short-day and long-day breeders:

Species that go into heat twice per year arediestrous.Canines are diestrous.[citation needed]

Monestrousspecies, such ascanids[17]andbears,have only onebreeding seasonper year, typically in spring to allow growth of theoffspringduring the warm season to aid survival during the next winter.

A few mammalian species, such asrabbits,do not have an estrous cycle, instead beinginduced to ovulateby the act of mating and are able to conceive at almost any arbitrary moment.

Generally speaking, the timing of estrus is coordinated with seasonal availability of food and other circumstances such as migration, predation etc., the goal being to maximize the offspring's chances of survival. Some species are able to modify their estral timing in response to external conditions.

Specific species

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Cats

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The femalecatin heat has an estrus of 14 to 21 days and is generally characterized as aninduced ovulator,since coitus induces ovulation. However, various incidents of spontaneous ovulation have been documented in the domestic cat and various non-domestic species.[18]Without ovulation, she may enter interestrus, which is the combined stages of diestrus and anestrus, before reentering estrus. With the induction of ovulation, the female becomes pregnant or undergoes a non-pregnantluteal phase,also known aspseudopregnancy.Cats are polyestrous but experience a seasonal anestrus in autumn and late winter.[19]

Dogs

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Main article:Canine reproduction

A femaledogis usually diestrous (goes into heat typically twice per year), although some breeds typically have one or three cycles per year. The proestrus is relatively long at 5 to 9 days, while the estrus may last 4 to 13 days, with a diestrus of 60 days followed by about 90 to 150 days of anestrus. Female dogs bleed during estrus, which usually lasts from 7–13 days, depending on the size and maturity of the dog. Ovulation occurs 24–48 hours after the luteinizing hormone peak, which occurs around the fourth day of estrus; therefore, this is the best time to begin breeding. Proestrus bleeding in dogs is common and is believed to be caused bydiapedesisofred blood cellsfrom the blood vessels due to the increase of theestradiol-17β hormone.[20]

Horses

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Main article:Horse reproduction

Amaremay be in heat for 4 to 10 days, followed by approximately 14 days in diestrus. Thus, a cycle may be short, totaling approximately 3 weeks.[21]Horses mate in spring and summer; autumn is a transition time, and anestrus occurs during winter.

A feature of thefertilitycycle of horses and other large herd animals is that it is usually affected by the seasons. The number of hours daily that light enters the eye of the animal affects the brain, which governs the release of certain precursors and hormones. When daylight hours are few, these animals "shut down", become anestrous, and do not become fertile. As the days grow longer, the longer periods of daylight cause the hormones that activate the breeding cycle to be released. As it happens, this benefits these animals in that, given a gestation period of about eleven months, it prevents them from having young when the cold of winter would make their survival risky.

Rats

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Rats are polyestrous animals that typically have rapid cycle lengths of 4 to 5 days.[22]Although they ovulate spontaneously, they do not develop a fully functioning corpus luteum unless they receive coital stimulation. Fertile mating leads to pregnancy in this way, but infertile mating leads to a state of pseudopregnancy lasting about 10 days. Mice and hamsters have similar behavior.[23]The events of the cycle are strongly influenced by lighting periodicity.[10]

A set of follicles starts to develop near the end of proestrus and grows at a nearly constant rate until the beginning of the subsequent estrus when the growth rates accelerate eightfold. Ovulation occurs about 109 hours after the start of follicle growth.

Estrogenpeaks at about 11 am on the day of proestrus. Between then and midnight there is a surge inprogesterone,luteinizing hormoneandfollicle-stimulating hormone,and ovulation occurs at about 4 am on the next estrus day. The following day, metestrus, is called early diestrus or diestrus I. During this day, thecorpora luteagrow to a maximal volume, achieved within 24 hours of ovulation. They remain at that size for three days, halve in size before the metestrus of the next cycle and then shrink abruptly before estrus of the cycle after that. Thus the ovaries of cycling rats contain three different sets of corpora lutea at different phases of development.[24]

Bison

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Buffalo have an estrous cycle of about 22 to 24 days. Buffalo are known for difficult estrus detection. This is one major reason for being less productive thancattle.During four phases of its estrous cycle, mean weight ofcorpus luteumhas been found to be 1.23±0.22g (metestrus), 3.15±0.10g (early diestrus), 2.25±0.32g (late diestrus), and 1.89±0.31g (proestrus/estrus), respectively. The plasma progesterone concentration was 1.68±0.37, 4.29±0.22, 3.89±0.33, and 0.34±0.14 ng/ml while mean vascular density (mean number of vessels/10 microscopic fields at 400x) in corpus luteum was 6.33±0.99, 18.00±0.86, 11.50±0.76, and 2.83±0.60 during the metestrus, early diestrus, late diestrus and proestrus/estrus, respectively.[25]

Cattle

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Female cattle, also referred to as "heifers"in agriculture, will gradually enter standing estrus, or" standing heat, "starting at puberty between 9 and 15 months of age. The cow estrous cycle typically lasts 21 days.[5]Standing estrus is a visual cue which signifies sexual receptivity formountingby male cattle. This behavior lasts anywhere between 8 and 30 hours at a time.[26]Other behaviors of the female during standing estrus may change, including, but not limited to: nervousness, swollenvulva,or attempting to mount other animals.[26]While visual and behavioral cues are helpful to the male cattle, estrous stages cannot be determined by the human eye. Rather, the stage can be estimated from the appearance of the corpora lutea or follicle composition.[27][28]

Estrous control

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Further information:Estrous synchronization

Due to the widespread use of bovine animals in agriculture, cattle estrous cycles have been widely studied, and manipulated, in an effort to maximize profitability through reproductive management.[26]Much estrous control in cattle is for the purpose of synchronization, a practice or set of practices most often used by cattle farmers to control the timing and duration of estrus in large herds.[4]

There is variation between the available methods of cattle estrous synchronization. Treatment depends on herd size, specific goals for control, and budget.[4]Some of theFDA-approved drugs and devices used to mimic natural hormones of the estrous cycle include, but are not limited to, the following classes:

  • Gonadorelin:There are currently five available gonadorelin products that are FDA-Approved.[29]Usually, gonadorelin is used in conjunction with another estrous control drug (typically, prostaglandin).[29][30]This drug is used to mimic gonadotropin releasing hormone (GnRH) and may also be used to treat ovarian cysts.[5]
  • Prostaglandin:Mimics the prostaglandin F2- Alpha hormone released when no pregnancy has occurred and regresses the corpus luteum.[5]This drug is used to achieve more consistent results in artificial insemination.[30]
  • Progestin:Used to suppress estrus and/or block ovulation.[5]Most commonly, it is administered via an intravaginal insert comparable to anIUD,which used in controlling menstrual periods.[31]It is also available as a medicated feed, but this method is not yet approved for cattle crop synchronization.[5]

There is variation between the available methods of cattle estrous synchronization. Treatment depends on herd size, specific goals for control, and budget.[4]

Bovine estrous cycles may also be impacted by other bodily functions such asoxytocinlevels.[32]Additionally,heat stresshas been linked to impairment of follicular development, especially impactful to the first-wave dominant follicle.[33]Future synchronization programs are planning to focus on the impact of heat stress on fertilization and embryonic death rates afterartificial insemination.[34]

Additionally, work has been done regarding other mammalian females, such as in dogs, for estrous control; However, there are yet to be any approved medications outside of those commercially available.[35]

Others

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Estrus frequencies of some other notable mammals:

See also

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References

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  1. ^Hill, M. A. (2021, April 6) EmbryologyEstrous Cycle.Retrieved fromhttps://embryology.med.unsw.edu.au/embryology/index.php/Estrous_Cycle
  2. ^abBronson, F. H., 1989. Mammalian Reproductive Biology. University of Chicago Press, Chicago, IL, USA.
  3. ^Llera, Ryan; Yuill, Cheryl (2021)."Estrous Cycles in Dogs".VCA Hospitals.RetrievedApril 6,2021.
  4. ^abcd"Synchronizing Estrus in Cattle - How does estrus synchronization work?".Texas A&M AgriLife Extension Service.Retrieved2021-03-22.
  5. ^abcdefMedicine, Center for Veterinary (2021-03-05)."The Cattle Estrous Cycle and FDA-Approved Animal Drugs to Control and Synchronize Estrus—A Resource for Producers".FDA.
  6. ^Panic of thesuitorsin Homer,Odyssey,book 22
  7. ^Plato,Laws,854b
  8. ^Plato,The Republic
  9. ^Herodotus,Histories,ch. 93.1
  10. ^abFreeman, Marc E. (1994). "The Neuroendocrine control of the ovarian cycle of the rat". In Knobil, E.; Neill, J. D. (eds.).The Physiology of Reproduction.Vol. 2 (2nd ed.). Raven Press.
  11. ^Heape, W. (1900). "The 'sexual season' of mammals and the relation of the 'pro-oestrum' to menstruation'".Quarterly Journal of Microscopical Science.44:1:70.
  12. ^Miller, Geoffrey (April 2007)."Ovulatory cycle effects on tip earnings by lap dancers: Economic evidence for human estrus?"(PDF).Evolution and Human Behavior.28(6):375–381.doi:10.1016/j.evolhumbehav.2007.06.002.
  13. ^Weir, Malcolm."Estrus and Mating in Dogs".VCA Animal Hospital.
  14. ^medilexicon > postpartum estrusArchived2016-03-04 at theWayback Machineciting: Stedman's Medical Dictionary. Copyright 2006
  15. ^Griffin, Brenda (December 2001)."Prolific Cats: The Oestrous Cycle"(PDF).Compendium on Continuing Education for the Practicing Veterinarian.23(12):1049–1056.
  16. ^Marcondes, F. K.; Bianchi, F. J.; Tanno, A. P. (November 2002)."Determination of the oestrous cycle phases of rats: some helpful considerations".Brazilian Journal of Biology.62(4A):609–614.doi:10.1590/S1519-69842002000400008.ISSN1519-6984.PMID12659010.
  17. ^Valdespino, C.; Asa, C.S. & Bauman, J.E. (2002)."Estrous cycles, copulation and pregnancy in the fennec fox (Vulpes zerda) "(PDF).Journal of Mammalogy.83(1):99–109.doi:10.1644/1545-1542(2002)083<0099:ECCAPI>2.0.CO;2.S2CID51812228.
  18. ^Pelicanet al.,2006
  19. ^Spindler and Wildt, 1999
  20. ^Walter, I.; Galabova, G.; Dimov, D.; Helmreich, M. (February 2011). "The morphological basis of proestrus endometrial bleeding in canines".Theriogenology.75(3):411–420.doi:10.1016/j.theriogenology.2010.04.022.PMID21112080.
  21. ^Aurich, Christine (2011-04-01)."Reproductive cycles of horses".Animal Reproduction Science.Special Issue: Reproductive Cycles of Animals.124(3):220–228.doi:10.1016/j.anireprosci.2011.02.005.ISSN0378-4320.PMID21377299.
  22. ^Hill, M.A. (2021, March 11) EmbryologyEstrous Cycle.Retrieved fromhttps://embryology.med.unsw.edu.au/embryology/index.php/Estrous_Cycle
  23. ^McCracken, J. A.; Custer, E. E.; Lamsa, J. C. (1999). "Luteolysis: A neuroendocrine-mediated event".Physiological Reviews.79(2):263–323.doi:10.1152/physrev.1999.79.2.263.PMID10221982.
  24. ^Yoshinaga, K. (1973). "Gonadotrophin-induced hormone secretion and structural changes in the ovary during the nonpregnant reproductive cycle".Handbook of Physiology.Vol. Endocrinology II, Part 1.
  25. ^Qureshi, A. S.; Hussain, M.; Rehan, S.; Akbar, Z.; Rehman, N. U. (2015). "Morphometric and angiogenic changes in the corpus luteum of nili-ravi buffalo (Bubalus bubalis) during estrous cycle ".Pakistan Journal of Agricultural Sciences.52(3):795–800.
  26. ^abcPerry, George (2004). Salverson, Robin (ed.)."The Bovine Estrous Cycle"(PDF).SDSU Extension.
  27. ^Ireland, James J.; Murphee, R.L.; Coulson, P.B. (1980)."Accuracy of Predicting Stages of Bovine Estrous Cycle by Gross Appearance of the Corpus Luteum".Journal of Dairy Science.63(1):155–160.doi:10.3168/jds.s0022-0302(80)82901-8.ISSN0022-0302.PMID7372895.
  28. ^Ginther, O. J.; Kastelic, J. P.; Knopf, L. (1989-09-01)."Composition and characteristics of follicular waves during the bovine estrous cycle".Animal Reproduction Science.20(3):187–200.doi:10.1016/0378-4320(89)90084-5.ISSN0378-4320.
  29. ^abMedicine, Center for Veterinary (2018-11-03)."Fertagyl® (gonadorelin acetate) - Veterinarians".FDA.
  30. ^ab"LUTALYSE® Injection (dinoprost injection)".zoetisus.Retrieved2021-04-06.
  31. ^"Hormonal Control of Estrus in Cattle - Management and Nutrition".Veterinary Manual.Retrieved2021-03-22.
  32. ^Armstrong, D.T.; Hansel, William (1959)."Alteration of the Bovine Estrous Cycle with Oxytocin".Journal of Dairy Science.42(3):533–542.doi:10.3168/jds.s0022-0302(59)90607-1.ISSN0022-0302.
  33. ^Wolfenson, D.; Thatcher, W. W.; Badinga, L.; Savi0, J. D.; Meidan, R.; Lew, B. J.; Braw-tal, R.; Berman, A. (1995-05-01)."Effect of Heat Stress on Follicular Development during the Estrous Cycle in Lactating Dairy Cattle1".Biology of Reproduction.52(5):1106–1113.doi:10.1095/biolreprod52.5.1106.ISSN0006-3363.PMID7626710.{{cite journal}}:CS1 maint: numeric names: authors list (link)
  34. ^Santos, J. E. P; Thatcher, W. W; Chebel, R. C; Cerri, R. L. A; Galvão, K. N (2004-07-01)."The effect of embryonic death rates in cattle on the efficacy of estrus synchronization programs".Animal Reproduction Science.Research and Practice III. 15th International Congress on Animal Reproduction.82–83:513–535.doi:10.1016/j.anireprosci.2004.04.015.ISSN0378-4320.PMID15271477.
  35. ^Kutzler MA. Estrous Cycle Manipulation in Dogs. Vet Clin North Am Small Anim Pract. 2018 Jul;48(4):581-594.doi:10.1016/j.cvsm.2018.02.006.Epub 2018 Apr 27. PMID 29709316.

Further reading

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