Standardized Care for Weanling Mice (Rodents)

IACUC Guideline
Effective Date: October 2023 
 

Purpose:

To standardize procedures for weaning mice in order to minimize adverse events associated with housing newly weaned animals.

IACUC Policy on Weaning

• Litters must be weaned by P21 and separated into same sex cages, unless pups are small or immature.
• Small sized or immature pups that may not be successfully weaned at P21 must not be weaned. The cage must be labeled with the new expected weaning date and other litters may not be born into the same cage. (Figure 1)
• Extended weaning (P22-P28) may be requested in the IACUC protocol under ‘Reportable Exceptions’ for strains that consistently require delayed weaning.
• A weanling is defined as any mouse under 31 days of age that has been weaned regardless of wean date.

Figure 1. New Litter Cards. Note location where expected date of wean can be entered by lab.

Weanling Care

• Avoid weaning on Fridays or before holidays unless a lab member will be present on the weekend or holiday to observe the animals.
• Labs are responsible for training weanlings to use the lixit. For cages with automatic water, the valve must be primed before placing the cage in the rack so that a drop of water is present on the valve. This will encourage the animals to learn to use the Lixit. (Figure 2)
• Each newly weaned cage is recommended to have new food placed in the feed hopper and 1-3 moistened food pellets on the floor of the cage. For Moistened pellet preparation, see “Small and Newly Weaned Weanlings” below.
• It is recommended to pre-shred the cotton nestlet prior to placing it in the cage to prompt nest-making.

Figure 2. Priming Lixit for Weanling Cages. Lixits should be primed at the time of weaning. For new weanlings, prime lixit more frequently. (Note: If a Lixit drips continuously, immediately remove cage from the Lixit to prevent flooding, and notify LARC.)

Small and Newly Weaned Weanlings

• Weanlings should be monitored daily by lab members until ability to independently eat and drink is confirmed. Weanlings that are small may need prolonged monitoring and care.
• Regardless of water source type, all weanlings should be provided with one half of a gel pack placed on the floor of each cage.
  • The gel packs should be changed out by the lab as often as needed, generally 2 to 3 times during the first week of weaning.
• Each newly weaned cage should have new food placed in the feed hopper and the equivalent of 1-3 moistened food pellets should be placed on the floor of the cage.
  • Moistened food preparation: preferably, ground food powder from the bottom of the food bin will be used to prepare moistened food. Add dry food to a dish or small paper cup and add a quarter of an inch of clean water to cover pellets. Allow pellets to soak for 3-5 minutes until water is absorbed. Add moistened food to cage floor.
  • Do not add dry pellets to cage floor and pour water on them. The water will get absorbed by the bedding instead of the feed.
• If animals appear dehydrated or weak, LARC veterinary staff should be contacted.