Enrichment

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Toys and chewable objects allow the
expression of species-typical
postures and activities

The environment in which animals used in science are housed should be designed to permit expression of strongly motivated behaviour patterns driven largely by internal stimuli such as changing hormonal levels. Environments which do not permit expression of these behaviour patterns result in a negative welfare state for the animal. Further improvement to the environment is generally termed 'environmental enrichment'. Enrichment of the research animal's environment means the provision of stimuli which promote the expression of species-appropriate behavioural and mental activities beyond that which is required to prevent the animal from suffering.

The concept of environmental enrichment is rooted in the following:

• Animals have physiological and behavioural needs. These needs are interrelated and their satisfaction affects physiological as well as behavioural responses, and thus well-being and experimental results.
• Complexity, control and predictability are essential elements for the successful establishment of an environmental enrichment program, i.e. specific consideration of each of these elements (including their mutual influence) is necessary when introducing environmental enrichment.
• For a valid design of an (new) enrichment program, it is of key importance to be familiar with the natural history of the species in question and to be aware of “sensitive” periods during development that may be opportunities for an effective enrichment strategy.

Categories of Enrichment

Hammocks can be used in cages
to make them more interesting
and stimulating to ferrets

Categories of enrichment include social (contact and non-contact), physical (complexity, sensory, and nutritional), and species-related strategies. The major factors to be considered are:

• opportunities to socialize or not
• opportunities to occupy time during waking hours
• opportunities to hide
• opportunities and structure for exercise

When introducing environmental enrichment, the natural history of the species should first be considered. This information should be used to support the introduction of appropriate social stimulation or objects in the animals' enclosure. The new level of complexity should provide the animal with the ability to extend its repertoire of behaviour, potentially increasing the welfare of the animal. A further increase in welfare may be obtained by adding the possibility for the animal to control the frequency or means of interacting with the introduced enrichment.

Concern is sometimes expressed that enrichment of an animal's enclosure may lead to variability in experimental results. However, more recent studies show that permitting an animal to express a wider range of behaviours may lead to a more "normal" animal and increase the validity of scientific data.

This section has been adapted from Baumans (2006) and Würbel (2007).

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