When does a mouse become sexually mature? - briefly
Female mice usually attain fertility at 5–6 weeks of age; male mice generally become reproductively capable at 6–8 weeks. The onset coincides with the completion of puberty and the first estrous cycle in females and the emergence of sperm production in males.
When does a mouse become sexually mature? - in detail
Sexual maturity in laboratory mice occurs during the post‑natal period known as puberty. In females, the first external sign is vaginal opening, typically observed between days 28 and 35. Estradiol levels rise sharply at this stage, accompanied by a surge in luteinizing hormone (LH) and follicle‑stimulating hormone (FSH). Ovulation becomes possible after the second estrous cycle, which usually takes place around day 42. Consequently, female mice are capable of successful mating and producing litters from approximately six weeks of age.
In males, preputial separation serves as the primary external indicator of puberty. This event appears between days 30 and 40. Testosterone concentrations increase markedly, driving the development of secondary sexual characteristics such as enlarged testes and seminal vesicles. Spermatogenesis reaches completion after the first wave of germ cell development, which is generally finished by day 45. Thus, male mice attain reproductive competence from roughly seven weeks onward.
Factors influencing the timing of maturity include:
- Genetic background: certain inbred strains (e.g., C57BL/6) mature slightly later than others (e.g., BALB/c).
- Nutritional status: caloric restriction or malnutrition can delay puberty, whereas excess energy intake may accelerate it.
- Environmental conditions: ambient temperature, photoperiod, and housing density affect hormonal regulation.
Monitoring of puberty in experimental settings relies on the two observable milestones listed above, supplemented by hormonal assays when precise dating is required. The window of reproductive readiness spans from the sixth to the eighth week of life, after which mice maintain fertility throughout adulthood unless affected by disease or experimental manipulation.