Rodent Weaning Guidelines

Rodent Weaning Guidelines

Weaning is a critical period in an animal’s life. Without maternal care, newly weaned rodents must be able to survive on their own. Transgenic and knockout animals often require special attention during weaning as they may be smaller and less vigorous than the normal animal.

LASC offers the following suggestions for weaning rodents. Please contact the animal unit supervisor or an LASC veterinarian if you have further questions or special needs.

  1. Rodents are normally weaned at 21 days of age. However, if you have animals that are small, slow in developing or otherwise compromised you may request a veterinary exemption for a longer period of time. Dams and sires must be separated before dams deliver new litters. This is to avoid rebreeding at the post-partum estrus. (Once the litter is weaned the dam may then be returned for breeding.) Prior progeny must always be separated from the mother before she gives birth to a new litter.
  2. A water source must be readily available for newly weaned rodents.
  3. Use “Napa Nectar” packs as an additional source of moisture. This is not intended to be a food source. Cut packet into several pieces and place one on a petri dish or small container on the cage bottom as needed.
  • Provide easy access to a food source for 1-2 weeks until rodents are capable of eating from the food hoppers. This can be accomplished in several ways:
  • Place food pellets directly on the cage bottom
  • Place moistened food on the cage bottom (in petri dish or small container). Moisten the food by soaking pellets in water until they soften or by mixing powdered chow with water to make a paste. Be aware that this food must be changed every one or two days to avoid contamination with feces or mold.
  • Supplement regular food pellets with commercially available diets such as “Transgenic Dough Diet” See Below. This is a soft, palatable, nutritionally balanced diet which is easy to use. It is available in sterilized (gamma irradiated) 1 kg packages. Place desired quantity on a petri dish in the cage bottom.
  • Napa Nectar is available for purchase from LASC.

    Transgenic Dough Diet is available from Bio-Serv.

    Breeding number calculations

    Normative data
    gestation time 19 – 21 days
    age at weaning 3 weeks
    age at sexual maturity 6 – 8 weeks
    approximate weight at birth 1g
    approximate weight at weaning 8 – 12g
    approximate weight of adult 30 – 40g (male > female)
    lifespan in laboratory 1.5 – 2.5 years
    average litter size 6 – 8
    total number of litters per breeding female 4 – 8
    useful breeding life of females 6 – 8 months
    useful breeding life of males 18 – 24 months
    Production data

    The following are indices that can be calculated to evaluate performance of individual mice or strains of mice. The breeding indices outlined below can be useful in determining when individual mice are in need of being replaced as breeding stock.

    Production data for Females
    Litter size = Average number of pups born per litter
    Wean rate = Average number of pups weaned per litter
    Whelping interval = Average time between births of litters
    Weaning interval = Average time between weaning of litters
    Production index = Average number of weaned pups per life of female
    Sex ratio = Ratio of weaned males to weaned females
    Production data for Males
    Plug rate = Number of plugged females/number of matings
    Pregnancy rate = Number of pregnancies/number of fertile matings.
    Sex ratio = Ratio of weaned males to weaned females
    Scientific data

    Record keeping for breeding mice should include:

    • Phenotype
    • Genotype
    • Strain designation (i.e. C57BL/6J, B6D2F1, etc.)
    • Breeder ID numbers – Each breeding animal should have a unique identifier that is not repeated in subsequent generations.
    • Set-up date (mating date)
    • Breeder date of birth (DOB)

    Reproductive Characteristics of Selected Inbred Strains

    Matings are considered productive if any offspring at all are born. Age at first mating refers to the age at which the first productive mating was recorded. Information for this chart was gathered from Mouse Genetics by Lee M. Silver (1995) and the Handbook on Genetically Standardized Jax Mice.

    Strain Name Productive Matings (%) Age at 1st Mating (wks.) Litter size (avg.) Number of Litters (avg.)
    129/SvJ 75 7.9 5.9 4.1
    A/J 65 7.6 6.3 2.9
    AKR/J 84 6.6 6.3 2.2
    BALB/cJ 47 8.0 5.2 3.8
    C3H/HeJ 86 6.7 5.7 2.9
    C57BL/6J 84 6.8 7.0 4.0
    CBA/CaJ 96 6.4 6.9 2.7
    DBA/2J 75 7.4 5.4 3.9
    FVB/N >90 9.5 4.8
    SJL/J 72 7.4 6.0 3.1