How many days does a rat's pregnancy last? - briefly
The gestation period for a typical rat lasts approximately 21 to 23 days.
How many days does a rat's pregnancy last? - in detail
The gestation period of the common laboratory rat typically lasts between 21 and 23 days, with 22 days representing the median value reported in most breeding colonies. This interval can vary slightly according to strain, environmental temperature, and maternal nutrition.
During the first week, embryonic implantation occurs and the conceptus establishes a connection with the uterine wall. By days 8–10, organogenesis is underway, and fetal limbs and craniofacial structures become discernible. The second week is marked by rapid growth; by day 14, fetal weight reaches approximately one‑third of the final birth weight. The final phase, days 15–22, involves maturation of the respiratory and nervous systems, accumulation of brown adipose tissue, and preparation for parturition.
Key factors influencing the exact length of gestation include:
- Genetic background: outbred strains such as CD‑I often exhibit a slightly longer duration than inbred strains like Sprague‑Dawley.
- Ambient temperature: temperatures below 20 °C can extend the gestational period by one to two days, whereas optimal housing at 22–24 °C promotes the standard 21‑23‑day range.
- Maternal diet: protein‑deficient or calorically restricted diets may delay parturition, while a balanced chow supports the typical timeline.
Litter size correlates inversely with gestational length; larger litters (10 + pups) may experience a marginally shortened gestation, whereas small litters (3–4 pups) can extend by up to a day. Post‑delivery, pups are born hairless, eyes closed, and weigh 5–7 g, requiring approximately 21 days of lactation before weaning.
In summary, the reproductive cycle of the rat is concise, averaging just over three weeks, with minor adjustments dictated by genetic, environmental, and nutritional variables. This predictable timetable underpins the species’ widespread use in biomedical research.