Colony Planning

It's important to determine the number of breeding pairs you need to supply sufficient mice for your experiments. The Breeding Colony Size Planning Worksheet (pdf) is a very useful resource.

Mating combinations

  • Mating pair- one male, one female; common for strains with good fecundity.  Leave pair together continuously, whenever possible, to maximize production.
  • Mating trio- one male, two females; maximizes cage space for breeding and mothers assist in raising each other’s pups. Leave trio together continuously, whenever possible.
  • Male rotation- single male placed with 1-2 female(s) per week; useful to quickly establish a colony. Once male is removed, do not return until pups are weaned.

Reproductive characteristics

Mating age:  6-8 weeks of age
Gestation:  ~19-21 days
Wean age:  ~21 days; up to 28 days if preferred
Litter size:  2-12 pups; highly strain-dependent
Replace breeders:  ~7-8 months of age (several mutant strains have considerably shorter windows of optimal breeding performance)

How to select appropriate breeding schemes

Homozygous mutant (-/-) x homozygous mutant (-/-):

Heterozygous mutant (-/+) x homozygous mutant (-/-)

  • Can be used if only one sex is viable and fertile as a homozygote
  • Offspring:  50% homozygous; 50% heterozygous; genotyping needed
  • Controls: see Considerations for choosing controls

Heterozygous mutant (-/+) x heterozygous mutant (-/+)

  • Must be used if neither sex is viable or fertile as homozygotes
  • Offspring: 25% homozygous; 50% heterozygous; 25% wildtype; genotyping probably required
  • Controls:  see Considerations for choosing controls

Timed Pregnant Females


Frequently asked questions

How many breeding pairs should I obtain to start my own colony?

A minimum of two to four breeding pairs are recommended for most strains; additional pairs are suggested for strains challenging to breed, or to expedite colony expansion.  Alternatively, it may be more cost-effective to have JAX provide study-ready mice for your experiments (see JAX® Breeding and Phenotyping Services).

What breeding information is available for JAX® Mice?

Consult the JAX® Mice datasheet for your strain of interest. Breeding performance is environment dependent; detailed baseline breeding statistics should be generated under your facility conditions.

My mice aren’t breeding well, what should I do?

See our Tips for poor breeders webpage.