1. a recurring period of sexual receptivity in female mammals, during which they are fertile and sexually receptive to males; heat.
Usage: biology; also spelled 'oestrum' in British English

Examples

• The veterinarian explained that the dog enters estrum approximately twice per year.
• During estrum, female mammals display behavioral and physiological changes that signal readiness to mate.
• Farmers monitor their cattle for signs of estrum to plan breeding schedules.
• The estrum cycle in horses typically lasts about 21 days.
• Hormonal changes trigger estrum in many mammalian species.