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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 ?
Scent Reflex Technology, a proprietary method to make the scents even more effective and longer lasting, is now used with Trail's End #307, Golden Scrape, Active Scrape and Golden Estrus Elk.
Key words: Non-descript cows; CIDR; PGF2[alpha]; Estrus synchronization; Artificial insemination; Pregnancy per AI.
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).
Based on this data, estrus response was observed and recorded as percentage of females showing estrus of total animals treated (interval from CIDR removal to onset of induced oestrus).
But does come into estrus whether it's hot, cold, windy or rainy--and they're almost always bred the first time they do so in a given year.
Another estrous urine worthy of a ride in your truck is 180 Day Estrus ($20) from Hunter's Specialties.
Last December, I successfully used an attractant of pure, pheromone-loaded estrus urine from a deer farm in Iowa.
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.
Hair ewes present estrus throughout the year; however, the wool ewes only present estrous in the fall and winter season: there are differences among breeds.
All females were inseminated twice (fist insemination was done 12 hrs interval after estrus onset and the thawed witn having minimum motility of 50-70%.