How fast does a mouse grow? - briefly
A laboratory mouse usually gains 2–3 g per week during its first month and reaches adult weight (≈20–30 g) by 6–8 weeks of age.
How fast does a mouse grow? - in detail
Mice reach adult size within a few weeks. Newborn individuals weigh 1–2 g and display a daily weight increase of roughly 0.5–1 g during the first ten days. By day 5 the mass typically doubles, and by the end of the third week most specimens attain 10–12 g, half of the expected adult weight. Full maturation occurs between five and eight weeks, when body mass stabilizes at 20–30 g for common laboratory strains and 15–25 g for wild‑type house mice.
Growth proceeds in distinct phases:
- Neonatal (0–14 days): Rapid somatic expansion, driven by high metabolic rate and abundant milk nutrients; weight gain averages 0.7 g day⁻¹.
- Pre‑weaning (14–21 days): Transition to solid food; growth rate slows to 0.3–0.4 g day⁻¹ while skeletal development accelerates.
- Post‑weaning (21–35 days): Continued increase in lean tissue; average gain of 0.2 g day⁻¹.
- Adolescent (35–56 days): Near‑adult size reached; weight gain falls below 0.1 g day⁻¹.
Key determinants of the growth trajectory include genetic background (e.g., C57BL/6 versus BALB/c strains differ by up to 20 % in final body mass), diet composition (protein ≥ 20 % of kcal maximizes growth), ambient temperature (thermoregulation demands reduce net gain below 20 °C), and hormonal milieu (growth hormone, IGF‑1, thyroid hormones). Environmental stressors such as crowding or pathogen exposure can suppress the rate by 10–30 %.
Laboratory measurements commonly employ longitudinal weighing at 2–3 day intervals, fitting the data to a sigmoidal (logistic) growth curve. The inflection point, occurring around day 20, marks the transition from exponential to linear growth, after which body mass approaches an asymptote representing adult size.
In summary, a mouse expands from 1 g at birth to 20–30 g within six weeks, with the fastest daily gains in the first week and progressively slower increments as maturity approaches. Genetic, nutritional, and environmental factors modulate each phase, producing measurable variation across strains and rearing conditions.