How many offspring do mice and rats have? - briefly
Mice typically produce 5–12 pups per litter, while rats usually have 6–12 offspring in each brood. Both species can breed several times annually, resulting in rapid population growth.
How many offspring do mice and rats have? - in detail
Mice and rats are prolific breeders. A typical laboratory mouse produces litters of 5 – 12 pups, with an average of about 7. Domestic strains may reach 14 or more. Gestation lasts 19‑21 days; females can become pregnant again within 24 hours after giving birth, allowing 6‑10 litters per year under optimal conditions.
Rats generate larger broods. Common laboratory rats average 8 – 12 offspring per litter, but numbers up to 20 have been recorded in well‑fed, healthy females. Gestation lasts 21‑23 days, and a female can produce 5‑7 litters annually when resources are abundant.
Factors that modify reproductive output include:
- Genetic background (inbred versus outbred lines)
- Age of the dam (peak fertility at 3‑6 months)
- Nutrition and body condition
- Seasonal light cycles and ambient temperature
- Stress levels and housing density
Under laboratory standards, a mouse colony can expand from a single pair to several thousand individuals within a year, whereas a rat colony can achieve comparable growth with fewer generations due to its larger litter size. In wild populations, average litter sizes are slightly lower because of limited food and higher predation risk, but the species retain the capacity for rapid population increase.