"Offspring" - what is it, definition of the term
The term “offspring” denotes the direct biological descendants of a rat or mouse pair, encompassing embryos, newborns, and juvenile individuals until they attain sexual maturity.
Detailed information
Rats and mice produce multiple young per reproductive cycle, commonly referred to as pups. Female rats (Rattus norvegicus) typically carry 6–12 pups, with a gestation period of 21–23 days. Female mice (Mus musculus) usually give birth to 5–8 pups after a gestation of 19–21 days. Litter size varies with strain, age, nutrition, and environmental conditions.
At birth, pups are altricial: hairless, eyes closed, and dependent on maternal care. Within 10–12 days, fur appears and eyes open. By the third week, they begin to explore the nest and exhibit coordinated locomotion. Weaning occurs between 21 and 28 days, when solid food replaces maternal milk. Sexual maturity is reached at 5–7 weeks for rats and 6–8 weeks for mice, enabling rapid population turnover.
Key developmental milestones:
- Day 0: Birth; weight 1.5–2.5 g (rat), 1.0–1.5 g (mouse).
- Day 10–12: Fur development; eyes open.
- Day 14–21: Solid food introduction; increased independence.
- Day 21–28: Weaning; separation from dam possible.
- Day 35–49: Onset of estrus in females; males exhibit increased territorial behavior.
Genetic considerations: each pup inherits half of its genome from each parent, allowing Mendelian inheritance studies. Inbred strains exhibit reduced genetic variability, which stabilizes phenotypic traits but may affect vigor and litter size. Outbred populations display greater heterogeneity, influencing growth rates and disease susceptibility.
Maternal behavior includes nest building, continuous grooming, and thermoregulation. Disruption of maternal care can alter stress responses and neurodevelopment in the young, highlighting the importance of a stable environment during the early postnatal period.
Health monitoring: common neonatal issues include hypothermia, dehydration, and congenital anomalies. Prompt identification of underweight or immobile pups enables intervention, such as supplemental warming or hand-feeding with specialized formula.
Overall, the reproductive efficiency of these rodents, characterized by short gestation, large litters, and early maturity, makes them valuable models for biomedical research and population studies.