How long does pregnancy last in domestic rats? - briefly
Pregnancy in domestic rats lasts approximately 21–23 days, with an average gestation period of about 22 days.
How long does pregnancy last in domestic rats? - in detail
Pregnancy in the common house rat (Rattus norvegicus) lasts approximately 21 – 23 days from conception to birth. The average gestation period is 22 days, but slight variations occur among strains, maternal age, and environmental conditions.
- Early gestation (Days 1‑7): Fertilized eggs implant in the uterine lining; embryonic cells begin differentiation. By day 5 the blastocyst is fully formed, and by day 7 the embryo establishes a connection with maternal blood supply.
- Mid‑gestation (Days 8‑14): Organogenesis proceeds rapidly. Limb buds appear around day 9, and the heart begins regular contractions by day 10. By day 13 the embryos are recognizable as distinct fetuses.
- Late gestation (Days 15‑22): Fetal growth dominates. Hair follicles develop, lungs mature, and the pups acquire body fat. The mother’s abdomen enlarges noticeably, and nesting behavior intensifies. The final 24‑48 hours involve preparation for parturition: cervical dilation, hormonal shifts (rise in prolactin, drop in progesterone), and increased uterine contractions.
Factors that can extend or shorten the gestation window include:
- Strain differences: Certain laboratory lines (e.g., Sprague‑Dawley) average 21 days, while outbred stock may reach 23 days.
- Maternal health: Malnutrition or severe stress can delay implantation, leading to a longer overall term.
- Temperature: Ambient temperatures below 20 °C may slow embryonic development, adding 1‑2 days.
- Parity: First‑time mothers often have slightly longer pregnancies than experienced breeders.
Typical litter size ranges from 6 to 12 pups, with larger litters sometimes associated with a marginally longer gestation. Parturition usually occurs during the dark phase of the light‑dark cycle; the entire delivery process lasts 30‑60 minutes, after which the mother cleans and nurses the newborns.
Understanding the precise timing of each developmental stage assists researchers in scheduling experimental interventions and helps breeders plan optimal housing and nutrition protocols.