Answer: ESTRUS

AnswerCrossword Clue
ESTRUSHeat
ESTRUSStage when an animal is in heat
estrusthe period of heat or rut; the period of maximum sexual receptivity of the female
estrusseries of physiological changes in sexual and other organs in female mammals, extending from one period of heat to the next, accompanied by behavioral changes indicating interest in mating
estrusthe period of heat in female mammals, also ESTRUM, OESTRUM, OESTRUS