How are mice bred? - briefly
Mice are bred in controlled laboratory colonies by pairing selected males and females in cages, monitoring estrous cycles, and weaning pups at about three weeks; genetic background, health status, and environmental conditions are recorded to preserve colony integrity.
How are mice bred? - in detail
Mouse breeding relies on controlled mating of selected individuals to maintain or develop genetic lines. The process begins with choosing a strain that matches experimental goals. Inbred strains provide genetic uniformity, while outbred stocks preserve heterogeneity. Hybrid crosses generate F1 progeny with defined heterozygosity, and backcrossing restores specific alleles.
Housing conditions must remain constant. Cages should be equipped with bedding, nest material, and enrichment. Temperature is kept between 20‑24 °C, humidity at 40‑60 %, and a 12‑hour light/dark cycle. Ventilation and cage cleaning schedules reduce pathogen load and stress.
Mating setups follow one of several configurations:
- Pair mating: one male with one female; optimal for small colonies, allows precise pedigree tracking.
- Harem mating: one male with two to three females; increases litter output, requires careful monitoring to prevent aggression.
- Timed mating: females are checked for estrus, then paired for a fixed period (usually 12‑24 h); enables precise gestational dating.
Detection of successful copulation is confirmed by the presence of a copulatory plug or by monitoring vaginal cytology. Once pregnancy is confirmed, females are housed singly to prevent disturbance.
Gestation lasts approximately 19‑21 days. Litters are born with 6‑12 pups on average. Within three days, pups are examined for health, sex, and any visible abnormalities. At 21 days, weaning occurs; pups are separated by sex and assigned to new cages for future breeding or experimental use.
Record‑keeping is essential. Each animal receives a unique identifier linked to its lineage, genotype, and health status. Health monitoring includes regular screening for common mouse pathogens (e.g., Sendai virus, mouse norovirus) and observation for signs of distress.
Genetic manipulation introduces additional steps. Embryo microinjection or CRISPR editing requires sterile surgical facilities, embryo transfer to pseudopregnant recipients, and validation of the intended modification by PCR or sequencing. Founder animals are backcrossed to a defined background for at least six generations to achieve genetic stability.
Overall, successful mouse breeding integrates precise selection, environmental control, systematic mating strategies, and rigorous documentation to produce reliable, reproducible animal models.