Humans have menstrual cycles rather than oestrous cycles. In contrast, females of species with menstrual cycles can be sexually active at any time in their cycle, even when they are not about to ovulate. This is also referred to as being "in heat". In species with oestrous cycles, females are generally only sexually active during the estrus phase of their cycle. Animals that have menstrual cycles shed the endometrium through menstruation instead. One difference is that animals that have oestrous cycles resorb the endometrium if conception does not occur during that cycle. However, species vary significantly in the detailed functioning. Mammals share the same reproductive system, including the regulatory hypothalamic system that produces gonadotropin-releasing hormone in pulses, the pituitary gland that secretes follicle-stimulating hormone and luteinizing hormone, and the ovary itself that releases sex hormones, including oestrogens and progesterone. įurther information: Menstrual cycle § Cycles and phases Naturally, estrous cycles are complemented by a rutting period of male counterparts within a species. Many mammals used in commercial agriculture, such as cattle and sheep, may have their estrous cycles artificially controlled with hormonal medications for optimum productivity. Some animals may display bloody vaginal discharge, often mistaken for menstruation. These cycles are widely variable in duration and frequency depending on the species.
Typically, estrous cycles repeat until death. Estrous cycles start after sexual maturity in females and are interrupted by anestrous phases, otherwise known as "rest" phases, or by pregnancies. The estrous cycle (from Latin oestrus 'frenzy', originally from Ancient Greek οἶστρος (oîstros) 'gadfly') is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females or non primates. Please consider expanding the lead to provide an accessible overview of all important aspects of the article. This article's lead section may be too short to adequately summarize the key points.