estrousphase

Estrous phase refers to the reproductive stage in female mammals during which the animal is fertile and receptive to mating. It is part of the estrous cycle, which in most species comprises four phases: proestrus, estrus, metestrus, and diestrus. Estrus, commonly called heat, is the period of sexual receptivity, and ovulation is typically near its end, though timing varies by species.

Hormonal regulation centers on estrogen and progesterone. Estrogen rises during proestrus and estrus, promoting receptivity and behavioral changes. A luteinizing hormone (LH) surge triggers ovulation. After ovulation, progesterone rises from the corpus luteum during metestrus and diestrus, supporting potential pregnancy or returning the cycle to proestrus if mating does not occur.

Signs and detection vary by species. Some animals show clear behavioral changes, while others rely on physical signs such as vulval swelling or discharge. In dogs, estrus lasts about 2–3 weeks with peak fertility near the middle. In cattle, the cycle is roughly 21 days, with a brief estrus. Rodents and other small mammals have shorter cycles. Seasonal breeders may have estrous cycles linked to day length.

Differences from human cycles are notable. Estrous cycles generally do not involve regular menstrual bleeding; ovulation timing and uterine changes differ from the human menstrual cycle.

Applications include planning breeding, timing artificial insemination, and managing contraception in veterinary and agricultural settings. Understanding the estrous phase helps optimize reproductive success and animal welfare.