Environmental Enrichment – Rats


Boston University is committed to observing Federal policies and regulations and AAALAC International standards for the humane care and use of animals.1 This policy provides guidelines for program of environmental enrichment (EE) for rats.

            Humane considerations and current policies require that research animals, whenever possible, must have the opportunity to interact with conspecifics and to benefit from EE.   Rats are social animals and, in contrast to mice, are much less likely to fight with cage mates.  Thus pair or group housing is a form of EE.  Rats are also intelligent, good learners that are capable of solving complex tasks. If handled gently from a young age they interact well with humans.  It is consistent with the goal of implementing and maximizing one of the three Rs, i.e. Refinement, to provide rats with EE. The use of individually ventilated cages (IVC) and barrier cages interferes with interactions based on smell, sight or noise from other conspecifics housed in the same room, making in-cage EE the norm for rats.


  • To define environmental enrichment for rats, including various ways to “facilitate the expression of species-typical behavior and promoting psychological well-being through physical exercise, manipulative activities or cognitive challenges”.1 
  • To outline how exceptions to this policy should be managed.


  • Compatible rats will be pair- or group-housed if space and body weight allows.  However, retired male breeders may require individual housing since they may be aggressive towards other males
  • If scientifically justified in an approved IACUC protocol, rats may be individually housed if required.  Unless otherwise indicated in the approved protocol, individually housed rats will be provided housing which allows visual, auditory and olfactory contact with other rats.
  • If a protocol exception to limit or exclude enrichment is to be included in an IACUC submission, the PI is required to consult with veterinary staff during protocol development to discuss the special circumstances that might limit participation in the enrichment program.  The Principal Investigator (PI) will need to include the requirement and scientific justification for single housing in the IACUC protocol, specify the approximate duration of single housing and/or the requested exemptions from any EE strategies included in this policy or associated SOP.  If no exemptions are approved within the protocol, then the policy and associated SOP will be followed.  Once the protocol is approved, the PI must inform animal facility personnel of the approved exceptions to this policy.
  • Certain medical or compatibility conditions may require that rats be individually housed or that other elements of the enrichment program be changed.  These determinations will be made by a veterinarian and documented in the animal’s record.  Veterinary exemptions to this policy do not require IACUC approval.
  • Singly housed rats are presumed to need more environmental enrichment than pair- or group housed rats and may be provided with extra cage enhancements unless an exception to limit or exclude EE is justified in an IACUC approved protocol for scientific reasons.  Singly housed rats will be observed daily and will have their well-being evaluated at least monthly by a veterinarian  or other adequately trained staff member.  The assessment and recommendations for continued single housing will be reviewed and approved by the Attending Veterinarian or designee.

Enrichment devices 

  • Several vendors provide an assortment of enrichment devices and treats.  These may include wooden chew sticks, Nyla bones, nesting material, Plexiglas tubes or other devices which fit in the cages without crowding the animals and can be either discarded at cage change or sanitized.
  • Facility staff will be responsible for the administration of the enrichment program including replacement of devices that are heavily soiled, malfunctioning, or in poor working condition.
  • If a PI has received approval in a protocol that the rats on study will receive edible treats for enrichment, this is best given by the PI or research staff as part of the study.  The administration of these edible treats should be clearly documented in the animal’s records.


1.   The Guide for the Care and Use of Laboratory Animals. 2011.  NRC ILAR.  P. 52-55.  Environmental Enrichment.

BU IACUC Approved: September 2011