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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 ?
3%, respectively, of vaginal smears of lactating cows during the 49-67 day period of the postpartum overt estrus cycle (Vasilenko 1999).
As a cow approaches estrus, a follicle containing an oocyte (egg) appears like a blister on an ovary.
Observations La Perforadora Behavior Year n First Last Males sexually active 2002 29 29 January 29 March 2003 26 26 January 26 March Estrus of females 2002 37 2 March 8 March 2003 34 3 March 9 March Gestation 2002 35 9 March 9 April 2003 30 8 March 10 April Nursing 2002 35 10 April 30 April 2003 30 11 April 2 May Weaning 2002 35 30 April 1 May 2003 30 2 May 3 May Observations Los Angeles Behavior Year n First Last Males sexually active 2002 28 28 January 27 March 2003 25 25 January 23 March Estrus of females 2002 44 4 March 9 March 2003 39 1 March 10 March Gestation 2002 44 10 March 10 April 2003 37 9 March 9 April Nursing 2002 44 11 April 5 May 2003 37 10 April 30 April Weaning 2002 44 5 May 5 May 2003 37 30 April 2 May
Developed through extensive testing, it's pure doe estrus urine, enhanced with all-natural doe secretions to create a potent scent that rutting bucks can't resist at that magical time of year.
Stephen Reese, one of Massachusetts' top bow hunters, shot an enormous 12-point buck -- one of the biggest of the year -- that revealed its presence by following an estrus scent into an open field in Sutton where a hot doe was regularly feeding.
After CIDR withdrawal, estrus was observed 3 times in a day (morning, afternoon and evening) until exhibition of overt estrus by placing a buck of proven libido.
Research also showed that non cycling cows can be identified - where the problem isn't when estrus is occurring but when it is not.
He stressed the need of awareness on estrus synchronization to enhance fertility in order to make dairy farming more profitable.
Also on Estrus but in a very different vein is the Midnight Evils LP Breakin' it Down.
These results were consistent with another study finding decreased estradiol production in cultures of minced ovaries from DEHP-treated rats in estrus (Laskey and Berman 1993).
Other animals receive estrogens, the primary female sex hormones, or progestins, semiandrogenic agents that shut down a female's estrus cycle.
According to the American Veterinary Medical Association, a drug called Estrus is used to temporarily prevent mares from coming into heat, but it would not be an effective weapon for date rapists.