Module 07 - Environmental Enrichment

Environmental Enrichment and Research Results

Improving the environment is not just a nicety for research animals.  There is a considerable body of literature now that demonstrates the influence of an animal's physical and social environment on research results.  One of the earlier demonstrations showed that social and physical stimulation of rats resulted in a thicker cerebral cortex with more dendritic connections.  Tumours in isolated mice grow faster than the same tumours in mice housed at appropriate densities.  Isolation of mice has been shown to increase the toxic effects of some drugs. 

It has also been shown that environmental enrichment is beneficial at any stage of an animal's life.  The effects may be different between young and old animals but the old will also benefit.  For this reason it is important to consider environmental enrichment as a variable in an experiment and to account for it.  It is not an option, however, to omit environmental enrichment to reduce the variables in a study unless the investigator is prepared to include all the deleterious effects of an impoverished environment on the study.  Even then, it would be difficult to say that the results represent the normal state of the animal.  However, if an investigator feels that attempts at environmental enrichment will jeopardise the results of a study, then this should be justified to the Animal Care Committee.

Environmental enrichment encompasses more than just the physical and social environment of a group of animals.  Because we interact with them at various levels, we may have a profound effect on their life.  We should treat animals in a manner that minimizes any discomfort or stress they may experience at our hands.  All the environmental enrichment in the world will not be of any value if an animal fears the arrival of a human being at its cage.  It may not be just the presence of a person but it may also include the sounds and smells associated with an experimental procedure, for example. 

Our activities in the animal facility may be disturbing, even if they do not directly involve the animals.  Noise is disturbing to animals and we should minimise extraneous noises as much as possible.  Some people bustle and have an air of urgency about them that is unsettling to animals.  Doors are allowed to slam shut or objects fall on the floor.  Equipment like cage washers, vacuums etc. may be upsetting, particularly to pregnant animals. 

If we try to see things as the animals might see them, we will probably be able to improve their living conditions.  In return, people working with the animals, particularly the animal care technicians, feel better about their jobs when they see the animals responding to their enriched environment.

It must be emphasised that changing an animal's environment, whether it be giving it a clean cage devoid of familiar "homey" smells or adding toys or other objects for enrichment, will be a variable that should be accounted for.  It is important, then, not to make changes to the environment without the agreement of the principal investigator and if changes are made, they should be applied consistently to all animals in the study.  It should be remembered that there may be effects of withdrawing enrichment, for example, if the animals move from a facility with very complex environments to one where there is minimal complexity.