How are rats born? - briefly
Female rats have a gestation period of about 21‑23 days, after which they give birth to a litter of 5‑12 hairless, blind pups. The neonates rely entirely on the mother for warmth, nutrition, and protection during the first few weeks of life.
How are rats born? - in detail
Rats reproduce through internal fertilization, beginning with a brief courtship that includes sniffing, vocalizations, and a rapid series of copulatory attempts. The male mounts the female, delivering a sperm packet (ejaculate) that travels through the cervix to the uterine horns, where fertilization occurs within minutes.
Gestation lasts approximately 21–23 days. During this period, embryonic development follows a predictable sequence:
- Days 1–5: Cleavage divisions produce a multicellular blastocyst; implantation in the uterine wall begins.
- Days 6–10: Organogenesis starts; the neural tube closes, and limb buds appear.
- Days 11–15: Eyes, ears, and facial features become distinguishable; skeletal ossification accelerates.
- Days 16–20: Fur begins to develop, and the pups acquire reflexes for suckling and thermoregulation.
A typical litter contains 6–12 offspring, though numbers can range from 2 to 14 depending on strain, nutrition, and maternal age. The pups are altricial: at birth they weigh 5–7 g, are hairless, and lack functional eyes. Their eyes open around day 13, and fur fully covers the body by day 15.
Parturition occurs in a nest constructed of shredded paper, cloth, or other soft material. The mother delivers each pup individually, usually in a succession of 5–10 minutes per offspring. She cleans each newborn with her mouth, stimulating respiration and removing membranes. Immediately after birth, the neonate begins to nurse; the mother’s milk provides essential antibodies (IgG) transferred via colostrum during the first 24 hours.
Post‑natal development proceeds rapidly:
- Days 1–7: Pups gain weight, develop thermoregulation, and exhibit rooting behavior.
- Days 8–14: Incisor eruption allows limited gnawing; pups start to explore the nest.
- Days 15–21: Weaning begins; solid food is introduced, and independence increases.
The entire reproductive cycle, from mating to weaning, can be completed in under two months, enabling rats to produce multiple generations annually. This efficiency underlies their status as prolific breeders in both wild and laboratory environments.