Approved by IACUC: 1/99
REVISED: 4/20/2005; 1/18/2006
Reapproved: 6/15/11; 3/28/2012
Based upon standards given in the Guide for the Care and Use of Laboratory Animals, rodent cages used in Einstein may hold the following combinations of animals:
Mouse cages have 70 in2 of floor space and may hold either:
- Five or fewer adult mice of less than 25 grams per mouse; or
- Two adult mice plus one litter of pups
- Rat cages (190 in2) can hold 3 adults up to 600 gram or one pair plus a litter. These cages cannot be used for harem breeding because they are too small to hold 3 adults plus one litter.
- Breeding cage (252 in2) can hold up to 5 adult rats but are used primarily for breeding rats (2 adults and a litter).
- Square cage (72 in2) are to be used for single housing rats.
Cages containing the following are considered overcrowded:
- More than 5 adult mice (weaned mice are considered adults).
- Three or more adult mice plus one litter of pups. IF HAREM BREEDING IS UTILIZED, PREGNANT FEMALES MUST BE REMOVED FROM THE CAGE PRIOR TO GIVING BIRTH.
- More than one litter in a cage. IF HAREM BREEDING IS UTILIZED, PREGNANT FEMALES MUST BE REMOVED FROM THE CAGE PRIOR TO GIVING BIRTH. If two females are allowed to whelp and which litter belongs to which dam cannot be distinguished, the two dams may be separated and the litters may be randomly split between the two dams in separate cages.
- A litter that appears to be weaning age (approximately 21 days old).
- More than 3 adult rats per regular (190 in2) cage
- More than 5 rats per breeder cage
- As above, either weaning age litter, > 3 adults with a litter, or multiple litters in a cage.
What happens when an overcrowded cage is discovered?
- IAS caretakers will flag overcrowded rodent cages using a two-part numbered blue card. IAS supervisory or veterinary staff will attempt to contact the investigator usually via phone or e-mail.
- For cages containing a single litter that appears to be weaning age (21 days) only, an investigator’s staff will be given 6 days from the date that the blue card is placed in which to separate the cage. After 6 days, IAS staff will perform this service for a fee of $5.00 per cage.
- For all other cases (> 5 adults, > 2 adults with a litter, multiple litters), investigators will be given only 1 day to correct the problem. If the problem is not corrected within this time period, IAS staff will perform this service the next morning for a fee of $5.00 per cage. If however, the overcrowding condition is severe and creates an immediate threat to animal well-being, IAS reserves the right to correct the problem immediately (the day they are detected) without prior notification.
Advice for avoiding overcrowding conditions:
- It is generally required as a condition of approval of any animal protocol that each investigator or a designated member of their staff must check their animals at least once per week.
- Most overcrowded cages are found and flagged by IAS caretakers during routine weekly cage change operations. Thus, a good time to check your rodent colonies is the day following the scheduled room change. This way newly placed blue “overcrowded cage” cards can be found and the problem corrected in a timely manner.
- The most severe overcrowding problems often result from harem breeding schemes in which several females become pregnant and have litters at the same time. Investigators who perform harem breeding should check their animal cages twice per week (e.g. Monday and Friday) to remove / separate near-term pregnant females from the group before they give birth.
- Under special circumstances, such as transgenic or mutant mice with low fecundity (low litter size or low pup survival), the Animal Institute Committee may approve co-housing of two adult females and their litters, to enhance pup survival. In this circumstance, the male should be removed from the cage just before the females give birth.
- In general, although harem breeding allows a breeding colony to be maintained with a relatively low number of breeding males, overall colony productivity (number of pups weaned) may be substantially lower than pair-breeding, when overcrowded conditions, especially multiple litters, result in increased pup mortality.