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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


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)



(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 period in female mammals during which ovulation occurs and the animal is receptive to mating.
References in periodicals archive ?
Table 1--Number of follicles (Num Fol) on Day 4 (D4) and Day 10 ( D10), follicle size on day 10 (D10), corpus luteum (CL) size on day 18 (D18) and ovulation rate of bos indicus cows submitted to an estrus synchronization protocol without (control) or with 300IU of equine chorionic gonadotrophin (eCG).
Residual levels on medroxiprogesterone acetate (MAP) impregnated sponges after estrus synchronization treatment in cyclic ewes.
To compare the effect of two estrus synchronization protocols (MGA[R] + PGF2[alpha] and Crestar[R]) in beef heifers.
In order to improve the reproductive performance of a herd, a strategy of estrus synchronization has been used in temperate cows for the last six decades, which facilitates AI with or without heat detection (Nebel and Jobst, 1998; Patterson et al.
These data indicate that CIDR with a sufficient amount of pFSH is an effective means of estrus synchronization for Boer crossbred does.
Residual levels on medroxyprogesterone acetate-impregnated sponges after estrus synchronization treatment and their relationship with fertility in cyclic goats.
Freitas VJF, Baril G, Bosc M, Saumande J (1996) The influence of ovarian status on response to estrus synchronization treatment in dairy goats during breeding season.
Present study compared two estrus synchronization protocols during low breeding season and recorded estrus incidence and conception rate after timed insemination in buffaloes that were exposed to a bull (BE, biostimulated) round the clock or not exposed to a bull (BN, not biostimulated).
Fertility of Bos indicus and Bos indicus x Bos taurus crossbred cattle after estrus synchronization.