How many mice are born at once? - briefly
A typical mouse litter consists of 5–12 pups, with 6–8 being most common. Litter size varies according to species, maternal age, and environmental conditions.
How many mice are born at once? - in detail
Mice usually produce a litter of several pups per delivery. For the common house mouse (Mus musculus) the average litter contains 5 to 7 individuals, with a standard deviation of about 2. Laboratory strains show similar averages, though selective breeding can shift the range to 4‑8 pups.
Factors that modify litter size include:
- Genetic background: Certain inbred lines have consistently larger or smaller litters.
- Female age: Young primiparous females often have 4‑5 pups, while females in their second or third estrous cycles commonly reach the 6‑7‑pup peak.
- Nutrition: High‑protein diets and ample caloric intake increase the probability of larger litters; poor nutrition reduces both litter size and pup survival.
- Season and photoperiod: In wild populations, longer daylight periods correlate with higher reproductive output.
- Health status: Parasitic load or disease can suppress ovulation and reduce the number of offspring.
The gestation period for most mouse species is 19‑21 days. After weaning, a female can become pregnant again within 24‑48 hours, allowing multiple litters per year. In optimal laboratory conditions, a single female may produce 8‑10 litters annually, resulting in a potential output of 40‑80 offspring per year.
Extreme cases have been documented. The world record for a single delivery in a laboratory mouse is 13 pups, achieved under controlled breeding and abundant nutrition. Wild mice rarely exceed 10 pups per litter due to environmental constraints.
In summary, the typical number of offspring per birth for domestic and laboratory mice lies between 5 and 7, with variability driven by genetics, age, diet, and environmental conditions. Maximum recorded litters reach the low‑teens, but such instances are exceptional rather than normative.