How many days until a rat gives birth? - briefly
The gestation period for a common rat is approximately 22 days, usually ranging between 21 and 23 days. After this interval, a female typically delivers a litter of 6–12 offspring.
How many days until a rat gives birth? - in detail
Rats have a relatively short gestation, typically lasting between 21 and 23 days from conception to delivery. The average is about 22 days, but several variables can shift this window.
- Species: The common laboratory rat (Rattus norvegicus) follows the 21‑23‑day range. Other species, such as the house mouse, have a slightly shorter period (approximately 19‑21 days).
- Strain differences: Certain inbred laboratory strains exhibit minor deviations; for example, the Fischer 344 strain may average 21.5 days, while the Sprague‑Dawley strain averages 22.5 days.
- Environmental temperature: Ambient temperatures below 20 °C tend to prolong gestation by up to 1‑2 days, whereas temperatures above 26 °C can shorten it slightly.
- Maternal age and health: Young or nutritionally compromised females may experience delayed parturition, whereas well‑fed, mature adults usually adhere to the standard timeline.
- Litter size: Larger litters can marginally extend the gestation period, often by 0.5‑1 day, due to increased physiological demand.
Pregnancy detection typically occurs around day 10‑12, when palpable abdominal swelling and changes in nipple coloration become evident. Ultrasonography can confirm fetal presence as early as day 7. Throughout the gestation, the female will exhibit nesting behavior, increased food intake, and hormonal shifts (elevated progesterone and prolactin) that prepare the uterus for parturition.
At the end of the gestation, contractions initiate around the 21st day, leading to delivery of pups over a period of 30‑60 minutes. The exact timing of each litter varies, but the overall process remains confined within the 21‑23‑day window under normal laboratory or domestic conditions.