Estrous Cycle

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Related to anoestrus: polyestrous

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 ?
Stagg K, Diskin MG, Sceenan JM and JF Roche Follicular development in long-term anoestrus suckler beef cows feed two levels of energy post-partum.
Anoestrus buffaloes, when compared with those resuming oestrus and from one month pre-partum to six months post-partum, showed higher serum urea concentration (46.
A high NEB in the periparturient and early post-partum period decreases luteinizing hormone (LH) pulse frequency, growth rate and diameter of the dominant follicle, insulin-like growth factor I (IGF-I), glucose and insulin concentrations and increases growth hormone (GH) and certain blood metabolites; these effects result in greater loss of BCS and a higher percent of anoestrus cows in the herd.