Back to List

Policy#: 529-277

Title: ANIMAL CARE / VIVARIA ISSUES: Policy on Environmental Enrichment

Effective: 10/19/2022


I: Related Policies and Guidance

·         Policy 529-271: Authority of the Attending Veterinarian

·         Policy 529-276: Investigator Care of Animals: A) Inside Vivaria; B) Outside Vivaria

II: Background

Environmental enrichment is required for all laboratory animals. The 8th edition of the Guide for the Care and Use of Laboratory Animals (Guide, pages 52-53) states that the "primary aim of environmental enrichment is to enhance animal well-being by providing animals with sensory and motor stimulation, through structures and resources that facilitate the expression of species-typical behaviors and promote psychological well-being through physical exercise, manipulative activities, and cognitive challenges according to species-specific characteristics.”

III: Definition

Environmental enrichment: additions to an animal’s environment with which it interacts. The goal is to allow animals to express a range of species-typical behaviors, which may enhance their well-being. Some examples of environmental enrichment include novel items (e.g., toys, food supplements/treats) and group housing of compatible animals.

IV: Policy

This policy outlines environmental enrichment materials or practices that may enhance species-specific behavior and reduce distress and anxiety for laboratory animal species at UCR.

The IACUC recognizes that there may be cases where environmental enrichment is not appropriate. It is recommended that the PI consult with the Campus Veterinarian on environmental enrichment alternatives. The UCR IACUC will review any concerns regarding environmental enrichment. Environmental enrichment exemptions may be granted via Veterinary discretion or when the scientifically justified exemption is included in the AUP for review and approval by the IACUC.

V: Implementation

A. Social Housing

The 8th edition of the Guide for the Care and Use of Laboratory Animals (Guide, page 51) specifies that social housing is the expectation for social species “Social animals should be housed in stable pairs or groups of compatible individuals unless they must be housed alone for experimental reasons or because of social incompatibility.” Single housing of social species should be the exception, justified on an AUP, and based on experimental requirements or concerns about animal welfare. The Guide also recommends that single-housed animals should be provided with additional enrichment, allowed to interact positively with animal care staff, and single housing is limited to the minimum period necessary.

Based on the above, the IACUC, in collaboration with OCV, requires that all animals housed at UCR be socially housed unless single-housing is either scientifically justified and documented in the approved AUP or needed due to one of the following:

·       Animals are separated due to aggression/fighting, medical treatment (e.g., administration of medication), or post-operative recovery.

·       Attrition that results in a single animal that cannot be repaired with other animals.

·       When animals are weaned by sex, and an animal is weaned alone due to incompatible gender (e.g., only one male in the litter).  

·       Breeding colony management-related issues include females separated for copulatory plug checks, males resting between mating, and the separation of pregnant mice in harem breeding settings to avoid cage overcrowding.

All other reasons for single-housing must be research-specific and documented in an approved AUP.

Below is a copy of what is found on all primary cage cards for animals housed at UCR. All labs are expected to document the reason and the date for single housing at the cage card level using this resource.










 Weaned Alone

In some cases, and for certain species (e.g., USDA-regulated species where single housing arrangements may be determined by or in concert with OCV), OCV may assist the PI in documenting the reason for single housing on the cage card or medical record.


Changes to the standard environmental enrichment described in the Table below are not permitted except under the following circumstances:

·      Changes are described in the animal use protocol and approved by the UCR IACUC.

·       Changes are prescribed by the OCV for animal health or welfare reasons.

The standard enrichment listed below may change in the future should novel opportunities and devices become known to the IACUC and/or OCV. Any such proposed changes will be announced prior to implementation, and feedback will be sought from investigators.

The IACUC Office will verify adequacy of sanitation procedures through ATP testing of items that are not disposable and/or edible. To facilitate sanitation, items should withstand cage washer procedures to allow OCV to assist with sanitizing enrichment devices. 

For all USDA-covered species (e.g., pigs, dogs, NHPs, rabbits, and any other warm-blooded animal except for mice of the genus Mus, rats of the genus Rattus, and birds), environmental enrichment and exercise will be conducted in accordance with the standards of the AWARs and in consultation with the investigator and campus veterinarian. Enrichment may include housing with compatible conspecifics, and provision of food treats, "toys" (e.g., plastic chains, balls, Kong toys, food puzzles, forage boards), and hiding places.


Species (common name)

Standard Environmental Enrichment


Additional Enrichment Allowed if Described in Approved AUP

(Provided by Research Group)


·         Group-housed if compatible

·         Nesting material made from paper or cotton fibers (e.g., Nestlets). 

·         Plastic mouse houses.

·         Edible treats such as cereal.


·         Group-housed if compatible.

·         Nylabone chewing toy.

·         Plastic rat houses.

·         Edible treats such as cereal


·         Group-housed if compatible.

·         Plastic chains or balls, stainless steel rings, PVC pipe.

·         Small portions of timothy hay, other grass hay, fresh carrots, or fresh kale are offered daily on the cage bottom.

·         Small amounts of other fresh vegetables, such as Romaine lettuce.

·         Small amounts of dried banana chips, apples, or pineapple.


·         Group-housed if compatible.

·         Positive human interaction daily (e.g., patting, scratching, rubbing back).

·         Multi-level shelves for resting and climbing.

·         Scratching posts, toys, and balls.

Guinea Pigs

·         Group-housed if compatible.

·         Small quantities of Timothy hay 2 to 3 times per week.

·         Plastic guinea pig houses.

·         Plastic balls or kongs.

Investigators are encouraged to develop and utilize the additional forms described in the Table, in addition to the standard methods described above. For species not listed in the Table, investigators are expected to consult with OCV to develop strategies to provide appropriate environmental enrichment. The approved AUP should describe the routine use of additional or alternative means of enrichment.

VI: References

1. The Guide for the Care and Use of Laboratory Animals, 8th edition, 2011.


Approved: 3/2/2009; 6/18/2018; latest revision 9/19/22