How many mice become pregnant? - briefly
Under standard laboratory conditions, roughly 80 % of sexually mature female mice become pregnant when paired with a male during a breeding period. The high conception rate reflects their short estrous cycle and prolific reproductive capacity.
How many mice become pregnant? - in detail
The proportion of adult female mice that achieve conception under standard laboratory conditions typically ranges from 70 to 90 percent. This figure reflects the baseline fertility of commonly used strains when mating pairs are introduced during the estrus phase.
Key determinants of conception success include:
- Age: females aged 6‑10 weeks exhibit the highest receptivity; fertility declines after 12 weeks.
- Genetic background: outbred strains (e.g., CD‑1) often surpass inbred lines (e.g., C57BL/6) in pregnancy rates.
- Health status: absence of pathogens, adequate nutrition, and stable body condition are essential.
- Environmental factors: consistent lighting (12 h light/12 h dark), temperature 20‑24 °C, and minimal stress improve outcomes.
Typical reproductive parameters for successful pregnancies are:
- Gestation period: 19‑21 days.
- Litter size: average 5‑8 pups; extremes can reach 12‑14 pups in prolific strains.
- Post‑partum interval: females become fertile again within 24‑48 hours after delivery.
Assessment methods for confirming pregnancy:
- Palpation of the abdomen after 10‑12 days post‑coitus.
- Monitoring of body‑weight gain; an increase of 2‑3 grams signals fetal development.
- Ultrasonography, providing visual confirmation from day 7 onward.
Optimizing conception rates involves:
- Pairing females with proven fertile males for 2‑3 nights.
- Ensuring estrus detection via vaginal cytology.
- Maintaining a clean, low‑density housing environment to reduce stress.
Overall, when optimal husbandry practices are applied, the majority of breeding‑ready females will become pregnant, resulting in robust colony expansion.