Choosing appropriate enrichment

Enrichment that works for one animal may not necessarily work for another – there are many factors to consider.

Importance of enrichment for research animals

Providing a good quality home environment is an essential component of laboratory animal management. A suitable environment for research animals allows them to perform a range of natural behaviours, including social behaviours, different sorts of locomotion, exploration, hiding and foraging. This will promote positive wellbeing, and can reduce the effects of any pain, discomfort or distress animals may experience.

Additionally, enriched environments can improve the ability of care staff to monitor animal welfare. This is because the wider behavioural repertoire shown by the animals makes it is easier to recognise changes that could indicate suffering, such as animals no longer using nesting material or deteriorations in nest quality.

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Choosing with the animal in mind

When choosing enrichment items, there may be specific behaviours you wish to encourage or inhibit (e.g. increasing foraging or reducing aggression). Alternatively, you may wish to demonstrate that a specific item is used (e.g. a novel shelter) or preferred (e.g. different types of nesting material). Your motivation combined with the requirements of the animals will inform the type of enrichment you choose.

Tables 1-3 below list some examples of enrichment items that could be appropriate for laboratory rodent species and zebrafish. Some of these items aim to satisfy basic behavioural needs of the animals (e.g. nesting material and something to gnaw for rodents). It is essential to consult with your manager before introducing any new enrichment items.

Before introducing/evaluating enrichment items, it is important to think about the specific needs of the animals in question. Tables 2 and 3 outline some special considerations (and potential refinements) for rodents and zebrafish used in different research contexts. Note that even if a form of enrichment has been validated for a particular species/strain/model in the literature, it may still require evaluation for the animals in your care (e.g. because the response to enrichment can differ depending on what else is provided within the cage, the group composition, and age of the animals).

It is also important to consider the sensory capabilities of the animals; for example, whilst humans and non-human primates are predominantly visual animals, rodents are more reliant on scent, and olfactory cues play an important role in reducing aggression in group-housed mice. For further information on the species-specific requirements and sensory capabilities of mammalian species, see our housing and husbandry pages; for resources on zebrafish, see our zebrafish welfare page.

The potential dangers of any enrichment item (e.g. the possibility of injury) should be carefully considered and assessed before incorporating it into your study plans. Hazards may not be immediately obvious. For example, certain types of bedding materials can irritate the eyes or cause respiratory problems. In an aquatic environment, some materials can leach chemicals into the water.

Table 1: Examples of enrichment for laboratory rodent species, with suggestions of how evaluation could be approached

Examples of enrichment

Type of evaluation

Notes

Nesting material 

B/P/M/U

Essential for all rodents

Something to gnaw

B/P/M/U Essential for all rodents

Shelter/tunnel/burrow

B/P/M Essential for all rodents

Social interaction

B/P/M Essential or preferred in most cases; male mice and female hamsters can require separating into subgroups if aggression cannot be addressed in other ways

Access to a 'playroom'

B/P/M Potentially suitable for all rodents

Scattered treats for foraging

B/P/M/U Potentially suitable for all rodents and particularly important for species that hoard food

Treat ball or puzzle

B/P/M/U Potentially suitable for all rodents to provide cognitive enrichment and encourage activity

Something to climb

B/P/M Potentially suitable for all rodents if reflective of climbing ability; mice, rats and hamsters can climb ropes, whereas gerbils and guinea pigs are more suited to ladders and ramps

Mezzanine or loft

B/P/M Potentially suitable to increase cage complexity and provide additional space

Running disc or wheel

B/P/M Potentially suitable but can be associated with stereotypical running behaviour

Background music

B Potentially suitable for the purpose of masking background noise

Key:

B = behaviour monitoring

P = preference testing

M = motivation testing

U = examining the enrichment item to see whether and how it has been used (e.g. weighing chew blocks or looking at nest quality)

Table 2: Examples of rodent research requirements, with suggestions for enrichment

Research requirement 

Special needs, if any 

Items/resources animals cannot have 

Possible alternatives 

Housing 

Sealed cages, e.g. IVCs 

None 

Opaque nest boxes – a clear view of the animals is needed for monitoring their welfare and to avoid having to open the cage 

Clear, tinted plastic nest boxes

Metabolism cages or metaboles

None 

Solid floors 

A solid resting area and/or a nest box fixed to the side of the cage, 2-3 cm above the floor 

Singly-housed animals 

Nest boxes and nesting material for feelings of safety and the ability to thermoregulate; foraging and other dietary enrichment to reduce boredom 

Access to other animals 

It may be possible to allow olfactory, auditory and visual (but not tactile) contact with other animals unless there is evidence that this will be a stressor; provision of mirrors

Instrumentation 

Head caps 

Avoid mechanical damage to head cap and wound margins 

Nest boxes that the animals can climb on, where they may rub the head cap against the cage roof; nesting materials that tangle around the head caps

Nest boxes that do not allow sufficient space for animals to climb on them; non-tangling nesting material; areas of low light within the cage

Cannulae, tethers or other restraints 

None 

Enrichment that the instrumentation could become stuck on, e.g. tunnels; nesting material with long, thick fibres

Nest boxes with wide doorways; non-tangling nesting material; areas of low light within the cage

Physical or psychological condition of the animals 

Immunocompromised animals 

Adequate hygiene standards must be maintained 

Enrichment items that cannot be appropriately sterilised 

Commercially available items that can be sterilised or autoclaved 

Nude animals 

Nest boxes and nesting material to aid thermoregulation 

Materials with cotton fibres, which can cause conjunctivitis 

Autoclaved paper towels or shredded paper for nesting 

Breeding animals 

Nest box and nesting material for security 

Materials that will entangle pups, e.g. cotton wool, wood wool, fine particles that stick to pups; very absorbent materials

Shredded paper; pulped cotton fibre 

Animals with impaired movement, e.g. because they are aged or have impaired motor function

Food, water and enrichment that is easy to access

Enrichment that encourages climbing too high, or includes small areas in which animals could become trapped

Nest boxes that animals cannot climb onto, with wide doorways; non-tangling nesting material; dietary supplements that are easy to handle and chew

Animals who may be in discomfort or pain, e.g. post-surgery, disease models, footpad injections

A comfortable and secure environment; nest boxes; appropriate litter and nesting material 

Opaque nest boxess, which result in more disturbance when monitoring the animals

Clear, tinted plastic nest boxes with wide doorways; non-tangling nesting material

Strains that are liable to behavioural problems, such as stereotypies or aggression

An environment that will take account of their behavioural needs, e.g. extra space and nest boxes to defuse aggression 

Needs to be judged on a case-by-case basis

Needs to be judged on a case-by-case basis

Table 3: Examples of enrichment options for zebrafish that have been highlighted in the peer-reviewed literature

See also Stevens et al., 2021.

Condition

Enrichment suggestions from peer-reviewed literature

Singly-housed fish 

  • Mirrors
  • Adjacent tanks with visual contact
  • Transparent perforated partitions for visual and olfactory contact
  • Artificial plants
  • Shelter

Breeding fish 

  • Artificial plants
  • Marbles as substrate

General/stock tanks 

  • Substrate (e.g. gravel, sand)
  • Adhesive images (e.g. of gravel substrate)
  • Living or artificial plants
  • Shelter
  • Live food
  • Graduated light levels
  • Classical music
  • Structural enrichment combined with waterflow

If there are concerns about chemical leaching, speak to your laboratory equipment supplier and, if necessary, ask for a ‘certificate of analysis’.