oestrous cycle (sexual cycle) The cycle of reproductive activity shown by most sexually mature nonpregnant female mammals except most primates (compare menstrual cycle). There are four phases: (1) pro-oestrus (follicular phase) – Graafian follicles develop in the ovary and secrete oestrogens;(2) oestrus (heat) – ovulation normally occurs, the female is ready to mate and becomes sexually attractive to the male;(3) metoestrus (luteal phase) – corpus luteum develops from ruptured follicle;(4) dioestrus – progesterone secreted by corpus luteum prepares uterus for implantation.

The length of the cycle depends on the species: larger mammals typically have a single annual cycle with a well-defined breeding season (they are described as monoestrous). The males have a similar cycle of sexual activity. Other species may have many cycles per year (i.e. they are polyoestrous) and the male may be sexually active all the time.

oestrus cycle (estrus cycle) In female mammals (other than most Primates, compare MENSTRUAL CYCLE) the hormonally controlled, regularly repeated stages by which the body is prepared for reproduction. In anoestrus the female reproductive apparatus is inactive; in pro-oestrus it becomes active; and in oestrus ovulation usually occurs (in some species ovulation is triggered by copulation) and the female becomes receptive to males. Unless fertilization occurs, oestrus gives way to anoestrus as the cycle repeats.

oestrus cycle(estrus cycle) In female mammals (other than most primates) the hormonally controlled, regularly repeated stages by which the body is prepared for reproduction. In anoestrus the female reproductive apparatus is inactive; in prooestrus it becomes active; and in oestrus ovulation usually occurs (in some species ovulation is triggered by copulation) and the female becomes receptive to males. Unless fertilization occurs, oestrus gives way to anoestrus as the cycle repeats.