When are mice sexually mature? - briefly
Laboratory mice become reproductively capable at roughly 5–6 weeks of age for females and 6–8 weeks for males. After this period they can successfully mate and produce offspring.
When are mice sexually mature? - in detail
Mice reach reproductive capability during the post‑natal period known as puberty. In females, the first sign of sexual maturity is vaginal opening, which typically occurs between 21 and 28 days of age. The initial estrus follows within a few days, and regular 4‑day estrous cycles are established by 5–6 weeks. In males, preputial separation marks the onset of puberty; this event generally appears between 28 and 35 days. Testicular growth, spermatogenesis, and detectable circulating testosterone usually complete by 6–8 weeks, after which mating behavior becomes consistent.
Several factors influence the exact timing:
- Strain: Inbred lines such as C57BL/6 mature slightly later (female 5–6 weeks, male 7–8 weeks) than outbred stocks like CD‑1 (female 4 weeks, male 6 weeks).
- Sex: Females consistently mature earlier than males across most strains.
- Nutrition: Caloric restriction delays vaginal opening and preputial separation by 2–3 days; high‑fat diets can accelerate or disrupt normal timing.
- Environmental conditions: Ambient temperature, photoperiod, and housing density affect hormonal regulation; standard laboratory settings (22 °C, 12 h light/12 h dark) produce the most reproducible maturation schedule.
- Hormonal status: Exposure to endocrine‑disrupting compounds can shift puberty onset earlier or later, depending on dose and timing.
Physiological markers used to confirm maturity include:
- Females: Vaginal opening, first estrus confirmed by cytology, ovarian follicle development, and luteinizing hormone surge.
- Males: Preputial separation, testicular descent, presence of mature sperm in epididymal smears, and rising serum testosterone.
Researchers typically schedule breeding experiments after these milestones: 5 weeks for female mice and 7 weeks for males, ensuring that both partners are capable of successful copulation and fertilization. Adjustments may be necessary for specific strains or experimental manipulations that alter growth rates.