Estrous Cycle

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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 It might be outdated or ideologically biased.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 ?
[F.sub.1] estrous cycles, breeding, fertility, and SP22 (a sperm protein biomarker of fertility) were unaffected, and [F.sub.2] litters showed no effects on pup weight or viability.
The use ofvaginal cytology in the Bottlenose dolphin (Tursiops truncatus) to monitor the estrous cycle. En: Proceedings of the 35th Annual International Association for Aquatic Animal Medicine Conference; 2004 Apr 4-9; Galveston, Texas (USA).
Baring in mind that endometrial IL-1[alpha] and IL-6 expression are upregulated in follicular phase of the estrous cycle, their promotion of endometrial cell proliferation and also that [E.sub.2] enhanced their support of PG production; it may be assumed that these cytokines may play a role in local changes, such as angiogenesis, cell proliferation, and other processes taking place in endometrium.
activity in female mammillary bodies were not evident between the phases of the estrous cycle studied.
When the IUAI was going to be applied in the Lewis rat colony once every 2 weeks during a six month period, vaginal wall impedance was measured for 25 females in the production colony using an estrous cycle monitor (EC-40, Fine Science Tools Inc., North Vancouver, Canada) equipped with a 4.8-mm-diameter probe designed for use in rats.
They are critical to sustain the function of corpus luteum during the estrous cycle. The PPAR response element has been found upstream of the COX-2 transcriptional site.
A review by Fillingim and Gear (2004) concluded that high levels of estrogens were associated whit decrease opioid analgesia among females, based on studies of rodents at different phases of the estrous cycle. Results of this find suggest that during the estrus stage, when circulating sex steroids are their lowest levels (MARCONDES et al., 2002) sensitivity to pain likely greater to those of the males and female proestrus.
This second phase is commonly referred to as the secondary rut, which involves the breeding of both non-pregnant mature does and yearlings that are just entering their first estrous cycles. In most cases, the secondary rut generally lacks the intensity of the primary rut, but it's still a great time to intercept a buck that has almost survived another.
This difference in pregnancy rates may be explained by a change in the progesterone-to-estrogen ratio between the first and third estrous cycles, resolving the early unfavorable uterine environment caused by higher progesterone and lower estrogen concentrations in the pubertal estrus (Byerley, Berardinelli, et al.