A phase in the sexual cycle of female animals characterized by their sexual receptiveness or their willingness for a coitus
Of or pertaining to sexual desire; mostly applied to brute animals; as, the oestrual period, oestrual influence
Oestrus is a phase in the sexual cycle (i.e. oestrous cycle) of female animals. It is characterized by sexual receptiveness in females. Females are said to be in heat during this phase. Other cues include a bloody vaginal discharge. Physiologically, the phase is regulated by gonadotropic hormones. When the ovarian follicles mature, estrogen is secreted. They then display behavioural manifestations indicating their sexual receptiveness.1
Oestrus begins following sexual maturity, and is interrupted by pregnancies and anestrous phases. Anestrous phase pertains to that period when the sexual cycle rests. Melatonin released from the pineal gland regulates reproduction. One of the factors controlling the release of melatonin is light exposure.
Word origin: Greek oîstros (mad desire)
1 Miller, G., Tybur, J. M., and Jordan, B. D. (2007). Evolution and Human Behavior. Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrus? Evolution and Human Behavior 28(6): 375–381.