Estrous Cycle

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Related to anoestrus: polyestrous

estrous cycle

[′es·trəs ‚sī·kəl]
The physiological changes that take place between periods of estrus in the female mammal.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Estrous Cycle


the aggregate of regularly-recurring changes in the reproductive system of female mammals. Characteristic synchronous changes in the entire female body and especially in the fallopian tubes, uterus, and vagina are governed by the rhythmic processes occurring in the ovaries (the development of the follicles, ovulation, and the formation of the corpus luteum). Each phase of the estrous cycle corresponds to certain changes in the mucous membrane of the vagina and in the cellular composition of the vagina.

The estrous cycle lasts 4–5 days in rats and mice, 16–17 days in guinea pigs, 21 days in cows, and 19–23 days in horses. The estrous cycle in rodents is conventionally divided into four stages—diestrus (the quiescent period), proestrus (preparation for estrus), estrus (heat), and metestrus (the luteal phase following estrus). During diestrus, which accounts for approximately one-half of the length of the entire estrous cycle, a smear shows a predominance of mucus and leukocytes. During proestrus, which lasts approximately 12 hours, the smear consists almost entirely of epithelial cells sloughed from the vaginal wall. During estrus, which lasts approximately 27 hours, the smear contains only squamous epithelial cells (anuclear, cornified cells). Animals normally mate only at the beginning of estrus. Metestrus lasts approximately six hours; during this stage the smear shows some leukocytes among the mass of squamous cells. Primates have a menstrual cycle.

The estrous cycle is observed only in animals with normally functioning ovaries. After neutering, diestrus sets in, and the other stages of the estrous cycle do not occur.


Eskin, I. A. Osnovy fiziologii endokrinnykh zhelez, 2nd ed. Moscow, 1975.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Seasonal modulation of puberty and postpartum anoestrus in cattle: a review.
A new intravaginal progesterone releasing device for cattle (CIDR-B) for estrus synchronization, increasing pregnancy rates and treatment of postpartum anoestrus. Anim Reprod Sci 33: 1-25.
[25.] Rhodes FM and SR Morgan Milk production and production worth of anoestrus dairy cows compared with their cycling herd mates.
Forcada F, Lozano JM, Abecia JA, Zaragaza L (1997) Control of luteinizing hormone secretion in ewes by endogenous opioids and the dopaminergic system during short seasonal anoestrus:role of plane of nutrition.
In the present study, history of anoestrus, abortions and delayed onset of estrus were also recorded in some of the dairy animals which were comparable to the findings of Gupta et al.
Heat stress causes hyperprolactinemia which results in reduction of luteinizing hormone secretion and oestradiol production in anoestrus buffaloes (Palta et al., 1997) leading to ovarian inactivity.
Influence of fenceline bull exposure on duration of postpartum anoestrus and pregnancy rate in beef cows.
In this view, Controlled Internal Drug Release (CIDR) device may hold the potential of enhancing the reproductive performance by combating the problem of anoestrus in post-partum cows (Vijayarajan and Meenakshisundaram, 2013).