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.

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.


References in periodicals archive ?
In the latter, it was possible to observe the different phases of the estrous cycle (Figs.
Data from real-time RT-PCR for ABCC1, ABCC9, SLCO4C1, and SLCO5A1 expression during the estrous cycle and pregnancy were subjected to least squares analysis of variance using the general linear models procedures of SAS (Cary, NC, USA).
A cellular and endocrine characterization of the original and induced corpus luteum after administration of a gonadotropin-releasing hormone agonist or human chorionic gonodotropin on day five of the estrous cycle.
The longer estrous cycle resulted from a longer diestrus phase, and shorter estrus and proestrus phases of the two experimental groups, as compared with the control group (p < 0.
The control of progesterone secretion during the estrous cycle and early pseudopregnancy in the rat: prolactin, gonadotropin and steroid levels associated with rescue of the corpus luteum of pseudopregnancy.
Sampling of the estrous cycle began exactly one week after neurological assessment battery to recover the baseline brain activity level and to avoid biased results.
According to literature reports, standardization of estrous cycle stage determination indicating adequate timing for service can be performed in two ways; microscopic evaluation of vaginal smears or impedance readings.
TABLE 1 Biometric parameters and number of macroscopic structures of the right and left ovaries in six collared peccaries, during the estrous cycle Follicular Phase (n = 3) Right ovary Left ovary Length (cm) 1.