How many mice are there in a litter? - briefly
A typical mouse litter comprises five to ten offspring, averaging six to eight pups. Litter size fluctuates with species, genetics, and environmental factors.
How many mice are there in a litter? - in detail
A mouse litter usually contains between five and twelve offspring. The most common range reported for laboratory strains such as C57BL/6 and BALB/c is six to eight pups per birth. Wild house mice (Mus musculus) display a broader spectrum, with litters as small as three and as large as fourteen, although the average remains around seven.
Factors influencing litter size:
- Genetic line – Inbred laboratory strains have relatively stable numbers; out‑bred or wild populations show greater variability.
- Maternal age – Young females (first or second estrus) often produce smaller litters; peak productivity occurs at 3–6 months, after which litter size gradually declines.
- Nutrition – Adequate protein and energy intake increase both the number of embryos implanted and the survival of fetuses.
- Seasonality – In temperate regions, breeding peaks in spring and autumn, correlating with larger litters due to favorable temperature and food availability.
- Health status – Disease or parasitic load reduces reproductive output, sometimes resulting in markedly fewer pups.
Counting procedures are straightforward: after parturition, pups are removed from the nest, identified by size and sex, and tallied. Litter size is recorded once all neonates are visible, typically within the first 12 hours. Researchers often note the number of viable pups versus stillbirths to assess reproductive success.
Statistical surveys of laboratory colonies report a mean litter size of 7.2 ± 1.4 pups, while field studies of wild populations indicate a mean of 6.8 ± 2.1. These figures provide a reliable benchmark for planning breeding programs, estimating population growth, and designing experimental protocols.