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Weaning of Mice

Adult mouse with weanling age pups

Weaning of Mice

In general, mouse pups should be weaned from their mother between 21-26 days of age. At this time, male and female pups must be separated into same-sex groups to avoid accidental breeding as the mice reach puberty. If litters are not weaned promptly, the cages will become overcrowded. If a litter is not weaned by 28 days of age, an ARP animal care technician will wean the animals and the investigator will be charged a fee.

If a mouse gives birth to a second litter before the first litter is weaned, the older litter must be removed (weaned) by the investigator. If after 48 hours, the older litter has not been weaned, the cage will be considered overcrowded and the litter will be weaned by an ARP animal care technician. The investigator will be charged a fee for weaning services.

Overcrowding of a cage may occur prior to weaning age if there are a large number of pups in the litter or if there are multiple dams/litters in one cage. Investigators should monitor large litters and move them with their dam(s) to a larger (gang) or separate cage if needed. This typically occurs when pups are around 10-14 days of age. If an ARP animal care technician is required to perform this duty, the investigator will be charged a fee.

Investigators often collect samples for genotyping at the time of weaning. However, DNA yield from tail tissue has been shown to be highest at 10-21 days of age. Tail tip amputation may only be used to collect tissue for genotyping in rodents less than 3.5 weeks of age. More information on genotyping procedures may be found on the ARP website.