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 ?
Bovine endometrium contains EPSI during the estrous cycle and pregnancy and production of EPSI is stimulated by bIFNT (Helmer et al.
1998) to evaluate THF-diol and/or LTX-diol effects on the estrous cycle in rats.
To determine whether endometrial S100G expression was affected by steroid hormones and during the implantation period in pigs, the uterine endometrial tissue explants from gilts on D12 of the estrous cycle were treated with [P.
Hormone concentrations from 60-day-old offspring in the diestrus stage of the estrous cycle are shown in Table 6.
These data indicate that the rate of luteal endothelial cell and pericyte proliferation was greatest earl), in the estrous cycle then decreased throughout the estrous cycle in a pattern similar to that of overall luteal cellular proliferation.
Twenty-four gilts were hysterectomized on D12 and D15 of the estrous cycle and D12, D15, D30, D60, D90, or D114 of pregnancy (n = 3 gilts/day/status).
In the present study we identified a second pair of mitogenic agents (LTX-diols) in HPLC peak II (Figure 2) from corncob bedding that also disrupt the estrous cycle of rats (Figure 8).
Beginning on the morning of days 13 of the estrous cycle (day 0=estrus), ewes received twice daily (morning and evening) intramuscular injections of follicle stimulating hormone (FSH; to induce superovulation) as follows: Day 13, 5 units/injection; Day 14, 4 units/injection; and Day 15, 3 units/injection.
Changes in plasma concentrations of immunoreactive inhibin, estradiol and FSH associated with follicular waves during the estrous cycle of the cow.
The concentrations of progesterone and estradiol across the estrous cycle and five days after ovariectomy and between HP and PP goats were analyzed by repeated samples ANOVA and as fitted to a generalized linear mixed model, using SPSS version 13.
Female mice adjacent to two male mice in utero, compared with those adjacent to two females, differ in terms of anogenital distance, activity level, body weight, estrous cycle length, age at sexual maturity, and other factors (vom Saal 1989).