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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 It might be outdated or ideologically biased.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 ?
Attempt was made to evaluate the cervical discharges of estrual and parturient animals to record pH, viscosity and microscopic observations.
Male rats will cross the grid and risk being shocked only when estrual females are used as stimuli.
Based on physical appearance, the estrual cervical vaginal mucus was categorized as purulent, muco-purulent and clear.
Sin embargo, algunos reportes en novillas y vacas adultas durante el periodo estrual, refieren una disminucion de magnesio sanguineo aun en animales suplementados [30].
Estrual cervico-vaginal mucus from each cow was collected before treatment and at subsequent estrus by recto-vaginal technique as per Dabas and Maurya (1988).
Las anomalias mas comunes que se han senalado por efectos de ambientes calidos son alteraciones en la regularidad y duracion del ciclo estrual, mayor frecuencia de incidencias de ovulos anormales, mortalidad embrionaria y en la tasa de abortos [2, 7, 16], Estos factores ambientales ademas, afectan directamente el comportamiento del animal, ya que a elevadas temperaturas disminuye la movilidad y el consumo de alimento [5] e indirectamente a traves de la disponibilidad de pasto la cual presenta un marcado efecto estacional [14, 15].
The present study was conducted to evaluate estrual cervical mucus of repeat breeding and normal cows under field conditions for bacterial flora, antibiotic sensitivity pattern and conception rate following treatment with specific antibiotics.
In replacement gilts case, the P4 concentrations for each one of the days of the sampling didn't present significance among them (P >0.05), observing 0.5 ng/ml like minimum value and 30.0 ng/ml like maximum value in the luteal phase of the estrual cycle.