How long is the gestation period for mice and rats? - briefly
Mice typically gestate for about 19–21 days, while rats have a slightly longer pregnancy of roughly 21–23 days.
How long is the gestation period for mice and rats? - in detail
The pregnancy of the common house mouse (Mus musculus) lasts about 19–21 days from conception to delivery. Most laboratory strains reach parturition on day 20 under standard conditions (22 °C, 12 h light/dark cycle, ad libitum chow). Embryogenesis proceeds through implantation around day 4, organogenesis from days 9–14, and fetal growth acceleration after day 15. Litter size typically ranges from 5 to 12 pups, with larger litters slightly extending the gestational interval.
The gestation of the Norway rat (Rattus norvegicus) averages 21–23 days. Standard housing conditions (20–22 °C, 12 h light/dark) produce deliveries on day 22 for most outbred and inbred strains. Key developmental milestones include implantation at day 5–6, limb bud formation by day 12, and rapid fetal weight gain from day 16 onward. Litters commonly contain 8 to 14 offspring; unusually large litters may add one or two days to the overall duration.
Factors that modify these periods:
- Strain genetics: Inbred lines often show narrower ranges than outbred stocks.
- Ambient temperature: Lower temperatures can prolong gestation by 0.5–1 day; higher temperatures may shorten it.
- Maternal nutrition: Caloric restriction or protein deficiency can extend the interval by 1–2 days.
- Parity: First‑time mothers usually have slightly longer pregnancies than experienced breeders.
- Stress exposure: Chronic stressors may delay parturition.
Comparative implications for biomedical research include the need to schedule interventions (e.g., drug administration, tissue collection) based on species‑specific timelines. Precise timing ensures alignment with critical windows of organ development, which differ by a few days between the two rodents. Accurate knowledge of these durations supports reproducibility and ethical management of breeding colonies.