How are mice and rats bred? - briefly
Mice and rats are propagated in controlled colonies by pairing healthy adults and allowing natural mating cycles, resulting in litters every three to four weeks. Standard practice supplies nesting material, a balanced diet, and regular monitoring of pregnancy to maintain offspring health.
How are mice and rats bred? - in detail
Breeding of laboratory mice and rats follows a controlled protocol to ensure genetic consistency, health, and reproducibility.
Mice are typically housed in ventilated cages with a bedding material that absorbs moisture and reduces ammonia. A standard breeding pair consists of one male and two to three females. Females are checked daily for a vaginal plug, indicating successful mating. After detection, the male is removed to prevent further copulation and to reduce stress on the females. Gestation lasts approximately 19–21 days; litters average 6–8 pups. Neonates remain with the dam until weaning at 21 days of age, at which point they are separated by sex to prevent premature breeding.
Rats follow a similar framework but differ in cage size, litter size, and gestation length. A typical breeding pair includes one male and two to three females, housed in larger cages with enrichment objects. Detection of mating relies on the presence of a copulatory plug or observation of mating behavior. Gestation for rats extends 21–23 days, producing litters of 8–12 pups. Weaning occurs at 21 days, with sex separation implemented thereafter.
Key management practices include:
- Genetic monitoring: regular genotyping to confirm strain integrity.
- Health surveillance: periodic testing for pathogens such as Mycoplasma and Sendai virus.
- Environmental control: temperature 20–24 °C, humidity 40–60 %, 12‑hour light/dark cycle.
- Record keeping: detailed logs of breeding dates, litter sizes, and weaning outcomes.
Selection of breeding stock is based on criteria such as age (8–12 weeks for females, 10–14 weeks for males), reproductive performance history, and absence of phenotypic abnormalities.
Artificial insemination is employed when specific genetic combinations are required. Sperm are collected from anesthetized males, diluted in a capacitation medium, and introduced into the female reproductive tract using a fine catheter. This method reduces the number of breeding pairs needed and accelerates the generation of desired genotypes.
Cryopreservation of embryos or sperm provides a backup for valuable lines. Embryos are harvested at the 2‑cell stage, cryoprotected with dimethyl sulfoxide, and stored in liquid nitrogen. Sperm are frozen in a glycerol‑based extender and similarly stored.
Overall, the breeding process integrates precise animal husbandry, rigorous health monitoring, and advanced reproductive technologies to maintain robust colonies for scientific research.