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Oestrous cycle

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The reproductive cycle in many female mammals (excluding humans) that is comprised of proestrus, oestrus, metestrus, diestrus, and anestrus phases


The oestrous cycle is the reproductive cycle of many female mammals. In humans, the reproductive cycle in females is the menstrual cycle. Oestrous cycle is similar to menstrual cycle in hormones (e.g. luteinizing hormone, estrogen, progesterone, gonadotropin releasing hormone, etc.) regulating the cycle and the reproductive structures involved. They differ though in a way that those with oestrous cycles reabsorb the endometrium in the absence of conception whereas those with menstrual cycle shed it through menstruation. Furthermore, animals with oestrous cycle are in heat only during the ouestrus phase of the cycle whereas those with menstrual cycle could still be sexually receptive at any time of their reproductive cycle.

The oestrous cycle is comprised of the following phases:

  • proestrus – the phase prior to oestrus and characterized by the development of the endometrium, the degeneration of the old corpus luteum, the distention of the uterus, the secretion of a sanguinous fluid, etc.
  • oestrus – the phase wherein the female is sexually receptive, and characterized by the lordosis reflex
  • metestrus– the phase characterized by the formation of the corpus luteum
  • diestrus – interval phase of sexual inactivity
  • anestrus - the phase when the sexual cycle rests


  • estrous cycle


See also: