👉 Oestrus is the menstrual cycle in mammals, typically occurring between 3-4 months after the onset of puberty and lasting until about 6 months before a female's first ovulation. It marks the end of her estrus period, marking the transition from a preovulatory state to an ovulatory one. This phase involves changes in hormone levels, including progesterone and estrogen, which are important for fertility and development in females during this time.