Mouse Colony Management

Investigators can breed their own colonies using the following RARC guidelines to get started.

Basic mouse breeding information

Mouse breeding can be very strain specific. The parameters below fit the majority of common strains of mice. It is advisable to get information from someone who has experience with a particular strain whenever possible.

  • age at sexual maturity: 5–8 weeks
  • reproductive lifespan: 7–12 months
  • estrus cycle: 4–5 days
  • gestation period: 19–21 days
  • average litter size: 6–8 pups
  • minimum weaning age: about 18–28 days
  • age of weaning is strain specific; C57BL/6 mice develop slower and generally require a weaning age of 24–28 days.

Mouse breeding record system: The Breeder Card

Mice can be paired at 6–8 weeks of age. When animals are paired for the first time, create a breeder card that includes a number unique to the pairing of these two animals. Write the unique number in the upper right-hand corner of the breeder card. This number is in sequential counting order starting from 1. Use a separate set of numbers per strain, so that you can quickly glance at the highest number and know how many breeding pairs you have of any given strain.

All offspring to be genotyped from this mating are given a unique number, called a DNA number, which consists of the breeder card number followed by the next sequential counting number starting from 1. This number is used to uniquely identify that animal for the duration of its time in the facility, and will be used on genotyping records, cage cards, etc. See a genotype report form and example.

Record the following on each breeder card:

  • Date paired - date mice are paired for breeding
  • Date separated - if separated, date male is removed from the female cage
  • DOB - record the date of birth for the pups born
  • # Born - total number of pups born (helps track productivity of pair)
  • ♂ - number of males that have survived at weaning time (optional)
  • ♀ - number of females that have survived at weaning time (optional)
  • Date weaned - date the litter was weaned

Repeat steps for each litter born.

When to replace breeders

  • when mice don’t produce a litter in 8 weeks of pairing or within 8 weeks of last litter
  • when mice do not raise 2–3 consecutive litters
  • when litter size rapidly decreases for 2 consecutive litters

The RARC Mouse Breeding Performance Checklist can be used to identify potential problems in your colony.

Mouse colony management calendar

To create a mouse colony management calendar:

  1. Establish a code, pairing color stickers with a corresponding event. For example, red = born; yellow = tail (PCR collection) and ear punch (identification); blue = wean; and green = nothing.
  2. Once a litter is born, chart the birth date and upcoming management activities by placing a color sticker on the appropriate date on a calendar.
  3. Each week look at the calendar to see what tasks have to be completed.
  4. Place the appropriate color sticker on the cage card for that week's activity.
  5. This schedule allows for tissue collection for genotyping and identification. If you do not need to genotype your mice, do nothing this week.
  6. Occasionally mice are born towards the end of the week and may not be ready to be weaned on Monday. If this is the case, allow for a few more days or until the mice are 18-24 days. Weaning age depends on strain of mice. Likewise if the mice are born in the beginning of the week, you will need to wean on Monday.
  7. It's good practice to check the colony on Mondays. Look at the color dot so you can plan your weekly tasks accordingly.

Get a Mouse Colony Management Calendar template.


Manual and course - The Jackson Laboratory has a great free PDF manual about breeding mice that can be downloaded: Breeding Strategies for Maintaining Mice Colonies

The AALAS Learning Library has a course called Mouse Breeding Colony Management.

Strain rederivation and cryopreservation services

The UW-Madison Transgenic Animal Facility offers strain rederivation and embryo or sperm cryopreservation on campus for a low cost. Contact Kathy Krentz at 890-3785 or

Genotyping and identification

See Policy 2010-038-v - Genotyping of Mice and Rats

Transnetyx is a molecular diagnostics company that offers an automated genotyping system for Transgenic, knockout and knockin mouse strains.