What is the gestation period of rats? - briefly
The gestation of a typical laboratory rat lasts about 21–23 days. Duration may vary slightly among species and environmental conditions.
What is the gestation period of rats? - in detail
The pregnancy of the common laboratory rat lasts approximately three weeks. Most strains deliver after 21 to 23 days, with 22 days representing the modal value. Variation of a day or two occurs among different genetic lines and under distinct environmental conditions.
Fertilization occurs in the oviduct within hours of mating. By day 5 embryos implant in the uterine lining, and the placenta begins to form. Organogenesis proceeds rapidly between days 10 and 15, when the fetal brain, lungs, and limbs become distinguishable. By day 18 the fetuses acquire most of their body mass, and the mother’s mammary glands enlarge in preparation for lactation. Parturition typically initiates in the early dark phase; each litter contains 6–12 pups on average, although extremes of 4 to 16 are reported.
Factors influencing the length of gestation include:
- Strain genetics – some inbred lines (e.g., Wistar) show tighter timing than outbred stocks.
- Maternal age and parity – first‑time mothers may deliver slightly later than experienced females.
- Nutrition and body condition – caloric restriction can extend gestation, whereas excess energy may shorten it.
- Ambient temperature – cooler environments tend to delay parturition by up to 24 hours.
Hormonal regulation centers on rising progesterone levels after implantation, followed by a surge of estrogen and prolactin that triggers uterine contractions and milk production. The final 24‑hour window before birth is marked by a sharp decline in progesterone and an increase in oxytocin, which coordinates the delivery of the pups.
Understanding these temporal milestones is essential for experimental planning, colony management, and the interpretation of developmental studies involving rodents.