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Social Housing of Animals Used in Research

Number: IACUC-POL-042 

Responsible Office: Office of Research and Creative Scholarship (ORCS) 

Applies to: All animal research and teaching protocols involving live vertebrate animals; PHS funded activities and USDA regulated species 

1. Purpose 

To establish institutional requirements for when animals may be singly housed, consistent with the Guide for the Care and Use of Laboratory Animals (the Guide) and the Animal Welfare Regulations (AWR). This policy defines acceptable justifications, documentation, monitoring, enrichment, and reporting for single housing and provides housing requirements for non‑social species. Social housing is the default for social species; single housing for social species is an exception to the Guide and must be justified, documented, time‑limited, and paired with mitigation measures. 

2. Background 

The Guide designates social housing as the default for social species and expects that any single housing will be limited to the minimum period necessary and justified by experimental requirements or animal wellbeing. OLAW requires institutions to identify and report IACUC-approved departures from the Guide in semiannual reports to the Institutional Official. The USDA’s AWR (9 CFR Part 3) defines species-specific standards for compatible grouping and environmental enhancement, including Subpart G for birds not bred for research. AAALAC International considers social housing the default and expects sensory contact and additional enrichment during necessary single housing. 

3. Definitions  

• Social species: Species that naturally live in stable pairs or groups (e.g., most rodents, rabbits, dogs, many birds/fowl, small ruminants). 
• Single housing: Housing one animal per primary enclosure without direct physical contact with a conspecific; may still allow sensory contact (visual/auditory/olfactory and, when appropriate, protected tactile contact).
• Nonsocial/solitary species: Species or life stages that are not normally kept in pairs or groups due to natural behavior or strong incompatibility tendencies.  

4. Roles and Responsibilities 

• Principal Investigators: Propose and justify any research-driven single housing in the protocol, minimize duration, and implement mitigation/enrichment as approved.  
• Attending Veterinarian (AV): Authorize welfare-based single housing, approve environmental enhancement plans (birds), review exemptions at specified intervals, and advise on repairing strategies.  
• Animal Care Staff: Implement cage/pen labeling, provide enrichment/sensory contact, conduct daily monitoring, and notify the AV/IACUC of concerns.  
• IACUC: Review and approve protocol justifications, audit use, durations, and mitigations during semiannual reviews, and ensure accurate reporting to IO/OLAW/USDA as applicable.  

5. Policy  

Social housing will be considered the default method of housing for social animals. Single housing of social species should be the exception and justified based on experimental requirements, veterinary-related concerns, animal well-being, or, in some cases, incompatibility issues. In these cases, it should be limited to the minimum period necessary. Singly housed animals should be provided with some degree of visual, auditory, and/or olfactory contact with other members of the same species. Exceptions to social housing will be reviewed on a regular basis by the IACUC (e.g., during annual and/or triennial review of protocols) and evaluated on an as-needed basis by the AV. 

6. Procedure 

General Procedures

Social animals will be housed in compatible pairs or groups, rather than individually, unless a single housing exemption has been documented on the cage card or Animal Use Protocol (AUP). Reasons for single housing may include: 

• Aggression 
• Attrition
• Clinical 
• Protocol Approved 
• Breeding 
• Weaned alone 

Aggression: Not all members of a social species are necessarily compatible. Social housing of incompatible animals can induce chronic stress, injury, and even death. Single housing of social animals due to aggression does not require specific protocol approval. Animals showing signs of conspecific aggression must be kept separate to minimize the risk of injury to other co-housed animals. For example, female hamsters, unfamiliar intact adult male: mice, rabbits, cats, horses, and chickens may not be housed together. Risks of social incompatibility are greatly reduced if the animals to be grouped are raised together from a young age, if group composition remains stable, and if the design of the animals’ enclosure and their environmental enrichment facilitate the avoidance of social conflicts. Social stability should be carefully monitored; in cases of severe or prolonged aggression, incompatible individuals need to be separated.  

Attrition: When animals are left singly housed due to attrition of cage mates on study, or uneven experimental group sizes, consideration should be given to re- housing with other conspecifics if possible, depending upon the expected duration of the study and/or individual species-specific considerations (e.g., housing unfamiliar male mice together is prohibited). When re-pairing is not possible without disrupting the study, single housing is acceptable for the remainder of the study. 

Clinical Reasons: Single housing of social animals, as directed by the AV or designee, and/or single housing post-operatively do not require a specific exemption approval in the relevant approved protocol. However, single housing must be for the minimum amount of time post-operatively necessary for recovery and/or healing as described in the animal care and use protocol or determined by the AV. Re-combining cages of adult male mice is contraindicated. Single housing for pre-anesthetic fasting does not require an exemption. In situations where the animal to be anesthetized is socially housed, pen/cage mates may be fasted as well to eliminate the stress of separation; this will also not require an exemption. 

Protocol Approved: If the protocol-driven need for single housing is necessary only for a portion of the study, the animals should be socially housed before and after that time. The timeframe for single housing should be specified in the protocol. 

Breeding: In many breeding arrangements, pregnant females may be housed singly prior to birth or immediately after birth. Female breeders may also have periods post weaning when they are single-housed prior to the next breeding. This does not need to be included in the IACUC protocol as an exemption, as it is understood that this is a necessary part of maintaining a breeding colony. Recombining cages of adult male mice is contraindicated as noted above. 

• If there are unbalanced litters (e.g., 4 females and 1 male) resulting in an animal not having an appropriate cage/pen mate at weaning, attempts should be made to identify a cage/pen mate of the same age. However, if this is not possible, a note should be made on the animal’s cage card. 
• Facility SOPs for colony and animal management should describe the breeding program, including the need for single-animal housing during periparturient times or other relevant time periods. 

If social housing of animals is not feasible because of the reasons above: 

• Singly housed animals should be provided with some degree of visual, auditory, or olfactory contact with other members of their species. Socialization with humans and regular positive human contact may also be beneficial and considered a form of enrichment. In some instances, one species can be used as a companion for another species (e.g., goats and horses), with IACUC approval. In the absence of other animals, additional enrichment may be offered. 
• Animal care staff, AV, and the IACUC are expected to monitor single housing exceptions and ensure that single housing is approved in the relevant protocol. 

7. References 

1. Guide for the Care and Use of Laboratory Animals (8th ed.)  
2. OLAW: Departures from the Guide —  
3. AAALAC Position Statements (Social Housing) — AAALAC Position Statements  
4. USDA AWR (9 CFR Part 3)   

8. Review, Approval and Version History