At what age do rats become sexually mature? - briefly
Rats attain reproductive capability around five to six weeks of age in males and six to eight weeks in females. This period marks the onset of functional gonadal activity and mating behavior.
At what age do rats become sexually mature? - in detail
Rats reach reproductive maturity during the early post‑natal period, but the precise timing differs between males and females and is influenced by strain, nutrition, and housing conditions.
In most laboratory strains, male rats exhibit the first signs of puberty between 40 and 50 days of age. Testicular enlargement, the appearance of sperm in the epididymis, and an increase in circulating testosterone mark this stage. By the sixth week, most males are capable of successful mating and produce viable offspring.
Female rats usually become fertile slightly earlier. Vaginal opening, a reliable external indicator of puberty, typically occurs between 30 and 35 days. Ovulation and regular estrous cycles commence within a week of this event, allowing conception as early as 40 days of age.
Key factors that modify these ages include:
- Strain: Sprague‑Dawley and Wistar rats mature slightly later than Fischer 344 or Long‑Evans strains.
- Dietary protein: High‑protein diets accelerate gonadal development; low‑protein regimens delay it.
- Housing density: Overcrowding can suppress hormonal release, postponing puberty.
- Photoperiod: Extended light exposure advances the onset of sexual maturation.
Hormonal profiling confirms these observations. In males, a surge in luteinizing hormone (LH) and follicle‑stimulating hormone (FSH) precedes testicular growth, while females display a pre‑ovulatory LH peak coinciding with vaginal opening.
Researchers planning breeding programs should schedule pairings after the earliest expected fertility windows—approximately 45 days for females and 50 days for males—to ensure successful conception while accounting for strain‑specific variations.