Animal Housing and Enrichment


The Public Health Service (PHS) policy on Humane Care and Use of Laboratory animals endorses US Government principles on use of Vertebrate Animals used in Testing, Research and Training, principle VII – “The living conditions of animals should be appropriate for their species and contribute to their health and comfort.” Based upon this, the Guide for the Care and Use of Laboratory Animals emphasizes “that animals should be housed with a goal of maximizing species-specific behavior and minimizing stress induced behavior”.

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 specific behavior and promote psychological well-being through physical exercise, manipulative activities, and cognitive challenges according to their species specific characteristics.

The environmental enrichment should be biologically relevant (i.e. hiding, gnawing, socializing, foraging, searching) so that it does not lose its enriching value over time. Environmental enrichment via physical manipulanda, structure, or substrate is preferred over nutritional enrichment.

All principal investigators working with laboratory animals are required to allow animal enrichment unless there is a scientific justification against the use of enrichment as approved by the Institutional Animal Care and Use Committee (IACUC). The justification must be included in an IACUC protocol submission and approved by the Attending Veterinarian (AV) and the IACUC.

Introduction of novel enrichment materials must be approved by the investigator and the AV before introduction.


Physical manipulanda are non-nutritive objects that ca be altered by the animal or encourage fine motor movements. These include plastic/nylon chew toys – the preferred standard method of rodent enrichment at CCM.

Manipulanda are sanitized at least as frequently as the animal’s primary enclosure (cage).

Structure and substrate includes objects that allow an animal to isolate itself into different microenvironments, experience varied textures or materials. These include nesting materials, running wheels and hiding shelters.

Structure and substrate are replaced or sanitized at least as frequently as the animal’s primary enclosure (cage).

Nutritional enrichment may be provided in lieu of physical manipulanda, structure or substrate if necessary for research purposes.

Nutritional enrichment is accomplished by provision of novel foods or provision of small pieces of the normal diet in the bedding to stimulate foraging.


Included in this are the Veterinarian Recommended Enrichment used currently at the CCM animal colony.

In addition, sometimes animals must be singly-housed due to various reasons such as incompatibility, pregnancy, surgery, medical isolation and other veterinary related issues.


  • Social Housing: Animals are group housed whenever possible. Male mice may be housed singly due to their aggresive nature.
  • Shelter: Nesting materials (e.g., Nestlets™); Igloos
  • Other: Nylabones™


  • Social Housing: Animals are group housed whenever possible. Male rats may be housed singly due to their aggressive nature.
  • Shelter: Tubes (polycarbonate); Nesting materials may be desirable for dams nearing parturition and during lactation.
  • Other: Nylabones™

Rabbits – most animals housed at CCM are male rabbits that are on surgical studies.

  • Social Housing: All male rabbits are singly housed at CCM animal facility.
  • Environmental Enrichment: Elevated shelves, toys (balls, bells, etc.)
  • Dietary Items: Food items (e.g., alfalfa cubes/timothy hay/lettuce)
  • Human Interaction: At least once a week, each rabbit becomes part of the human socialization program. The socialization consists of petting, brushing, to get the animals acquainted with human handling. Brushing reduces potential for hairballs.


  • Social Contact: Group housed as much as possible; pair – or group-housed hamsters of same gender, except for pregnant females and incompatible animals.
  • Nesting Material: Nestlet, tissue papers
  • Other: Igloo, Jolly Ball™


  • Being a prey species, Xenopus leavis are provided with shelter objects. The enrichment for X.leavis colony is the provision of PVC pipes. For the group housed X.leavis the number of enrichment (PVC) pipes depends on the density of the animals in the tank.
    • 1 to 5 frogs – 1 PVC pipe
    • 5 to 10 frogs – 2 PVC pipe


  • The primary method of environmental enrichment is to be socially housed.  The use of artificial plants or other objects has been shown to have an effect on various aspects of fish metabolism.  If any artificial object is requested for the enrichment of fish requires the approval by the CCM Attending Veterinarian.

Implementation and Assessment

A successful well-being program depends on not only implementing but also on evaluating its effectiveness, and constant update to reflect our current knowledge. The principal investigators, research staff, veterinary staff and animal care technicians are involved at all times in decisions regarding psychological well-being and environmental enrichment.


  1. Environmental strategies for laboratory animals. ILAR, Vol 46 (2), 2005.
  2. “An Enriched Environment For The African Clawed Frog (Xenopus laevis)”: Lab Animal Magazine, May 1993, Vol. 22, Number 5, pp. 25-29.
  3. Environmental enrichment program for hamsters. Institutional Animal Care and Use Committee, Cornell University, Ithaca, NY.
  4. Guide for the Care and Use of Laboratory Animals – 8th edition. National Research Council, Washington DC.
  5. Public Health Service Policy on Humane Care and Use of Laboratory Animals, OLAW, NIH.

Effective Dates:      December 7, 2023 through December 31, 2026