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(US), estrus, estrum
a regularly occurring period of sexual receptivity in most female mammals, except humans, during which ovulation occurs and copulation can take place; heat
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


The period in mammals during which the female ovulates and is receptive to mating. It is commonly referred to as rut or heat. From one estrus period to the next there occurs a series of changes, particularly in the ovary, uterus, and vagina, termed the estrous cycle. With reference to the ovary, the cycle can be divided into a follicular phase, during which the Graafian follicles are ripening, and a luteal phase, during which the corpora lutea develop in the ovulated follicles. During these two phases, mainly estrogen and progesterone, respectively, are secreted, and these hormones control the uterine and vaginal changes. The beginning of the follicular phase is termed proestrus, and the luteal phase metestrus. Following the latter, there is a period of relatively little change, termed diestrus. In species in which the latter is prolonged, it is termed anestrus. See Estrogen, Reproduction (animal)

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(also heat or rut), a stage in the sex and reproductive cycle, or period of sexual activity, in female mammals. Estrus recurs regularly before coitus at intervals characteristic for each species of animal—several days, weeks, or months. During estrus the mating instinct is aroused, and in most mammals ovulation occurs at the end of estrus. In polyestrous animals, estrus recurs periodically throughout the year. In mice and rats, for example, it occurs every four to six days; in guinea pigs, every 18 days; and in cows, every 21 days. In monestrous animals, it occurs once or twice a year, as in dogs and foxes. During estrus, morphological changes occur in the vagina and uterus; they are especially marked in such rodents as mice, rats, and guinea pigs.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


The period in female mammals during which ovulation occurs and the animal is receptive to mating.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The effects of synchronization treatments on expression of estrus are very important aspects that need to be considered when designing strategies for controlled breeding programs (Quezada-Casasola et al., 2015), keeping in view that both hormonally-induced, and naturally-occurring estrus may differ among different types and breeds of cattle (Zarate-Martinez et al., 2006).
Protected fatty acid supplementation during estrus synchronization treatment on reproductive parameters of dairy goats.
The Panotico and Giemsa staining methods were efficient, allowing the identification of different types of vaginal epithelial cells of Santa Ines ewes during the estrus period.
When you look at the October 15 through November 4 period, just prior to estrus, 40 percent of bucks wander from their home range.
Estrous behavior and the estrus-to-ovulation interval in Nelore cattle (Bos indicus) with natural estrus or estrus induced with prostaglandin F2[alfa] or norgestomet and estradiol valerate.
Cytological features following vaginal smear represent each stage of estrous cycle Stage of Nucleated Squamous Cornified squamous estrous cycle epithelial cells epithelial cells epithelial cells Proestrus + - - Estrus - + - Metestrus - - + Diestrus - - - Stage of Leukocytes estrous cycle Proestrus - Estrus - Metestrus + Diestrus + Proestrus, predominantly consisting of nucleated epithelial cells; estrus, with cornfield squamous epithelial cells; metestrus, consisting of cornified squamous epithelial cells and predominance of leukocytes; and diestrus, consisting predominantly of leucocytes Table 2.
All adult females were found to be reproductively active throughout the year, either in pregnancy (51%), lactating (20%), or reproductive (29%, in the estrus or proestrus phases of the reproductive cycle).
With so few females in estrus, there's increased competition for them.