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 ?
Different types of oestrous cycle in two closely related South American rodents (Cavia aperea and Galea musteloides) with different social and mating systems.
Expression of oxytocin, oestrogen and progesterone receptors in uterine biopsy samples throughout the oestrous cycle and early pregnancy in cows.
The mean number of corpora lutea was significantly different between the oestrous cycle phases, being highest in the luteal phase (2.
Effect of stress due to ultrassonography on plasma cortisol and progesterone (P4) concentrations during oestrous cycle in ewes.
The synchronization of oestrous cycle in sexually mature rats was induced using the Whitten effect (Whitten 1956; Whitten et al.
This distribution guaranties a similar number of females of the different oestrous cycle stages in each experimental group.
Pituitary and plasma vasopressin concentrations and fluid balance throughout the oestrous cycle of the rat.
Pseudo pregnancy happens because at the end of one of the stages in the oestrous cycle of the bitch, the pituitary gland in the brain produces a hormone called prolactin.
It has been known for centuries that animals and birds have what is called a sexual season, an oestrous cycle, and that this is recognized by natural signs and patterns of behaviour by both the male and female of the species.
Progesterone, oestradiol-17 and LH during the oestrous cycle of muskoxen (Ovibos moschafus).
In contrast with fully fed animals, no extension in oestrous cycle length is observed with ageing in food-restricted animals and normal cyclicity is continued to an age when control animals have ceased to cycle and have entered reproductive senescence [5].