Estrous Cycle

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Related to Oestrous cycles: metestrus

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 ?
Modification of the oestrous cycle of the mouse by external stimuli associated with the male.
In rats with oestrous cycles extended to 6 days, the plasma concentration of oestradiol-17[beta] rises early in relation to the timing of ovulation.
No data are available to compare fully-fed and dietrestricted animals on the numbers of primordial follicles recruited to grow during subsequent oestrous cycles.
A comparison of the oestrous cycle hormonal profile between control and diet-restricted animals, at an age when control animals are beginning to show the first hormonal changes associated with the initial phase of reproductive senescence, revealed two significant differences.
In buffaloes, ovarian follicular dynamics during the oestrous cycle is similar to that in cattle.
Influence of level of nutrition and season on the oestrous cycle rhythm and on fertility in buffaloes.
In contrast to more temperate climates, frequencies of oestrous cycles and conception rates were significantly higher during the winter months.
1, oestrous cycles (n = 13) in eight buffaloes were monitored.
The data of spontaneous luteolysis were obtained from the ovulatory waves of oestrous cycles of experiment 1 (n = 12).
Cell-specific localization of progesterone receptors in the bovine ovary at different stages of the oestrous cycle.
Serum and oestrual cervical mucus bio-chemical profile during oestrous cycle in repeater cross bred cows.
The effect of Trypanosome evansi infection on the oestrous cycle of Friesian Holstein heifers.