How do mice and rats reproduce? - briefly
Females become fertile every 4–5 days, with gestation lasting 19–21 days; each birth produces 5–12 pups. Multiple litters can occur throughout the year, allowing rapid population growth.
How do mice and rats reproduce? - in detail
Mice and rats reproduce through a rapid, season‑independent breeding cycle that maximizes population growth. Sexual maturity is reached at 5–8 weeks for mice and 8–12 weeks for rats, after which individuals are capable of successful copulation.
Females exhibit a 4‑day estrous cycle. Ovulation occurs spontaneously at the end of the proestrus phase, triggered by a surge of luteinizing hormone. Mating typically takes place during the dark phase of the light cycle, when both sexes are most active. The male mounts the female, intromits, and delivers a sperm‑rich ejaculate; the average copulatory bout lasts 3–5 minutes.
Fertilization takes place in the oviduct. After conception, the embryo implants in the uterine wall within 5 days. Gestation lasts 19–21 days in mice and 21–23 days in rats. Litter size averages 5–8 pups for mice and 6–12 pups for rats, though extremes of 2–12 and 4–20 respectively have been recorded.
Neonates are altricial: hairless, eyes closed, and reliant on maternal care. Pups are weaned at 3 weeks (mice) or 4 weeks (rats). Females can become pregnant again within 24 hours of giving birth, a phenomenon known as postpartum estrus, enabling overlapping litters.
Key reproductive parameters:
- Sexual maturity: 5–8 weeks (mouse), 8–12 weeks (rat)
- Estrous cycle length: 4 days
- Ovulation: induced by luteinizing hormone surge
- Copulation duration: 3–5 minutes
- Gestation: 19–21 days (mouse), 21–23 days (rat)
- Average litter size: 5–8 (mouse), 6–12 (rat)
- Weaning age: 3 weeks (mouse), 4 weeks (rat)
These biological characteristics ensure that both species can sustain high reproductive rates under favorable conditions.