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3R-Project 66-99

The influence of enriched housing conditions on experimental results in laboratory mice

Vera Baumans and H.A. van de Weerd
Department of Laboratory Animal Science, Faculty of Veterinary Medicine Utrecht University, 3508 TD Utrecht, The Netherlands

Keywords: mice; ethology: laboratory animals; ethology: enrichment; reduction; refinement

Duration: 1 year Project Completion: 2001

Background and Aim
National laws, international guidelines and conventions on minimal housing conditions for laboratory animals require that the environments of animals meet their physiological and behavioural needs, as well as ensuring their health.
The environments of laboratory animals are standardised in order to reduce variation in the results, especially in regulatory studies performed during the development and registration of pharmaceutical products and chemicals. It has been questioned whether these standardised laboratory environments promote the well-being of the animals. In 'enriched' environments, the animals can perform more natural, species-specific types of behaviour. Enrichment provides the animal with a more stimulating and responsive environment such as cage mates, nesting material, hiding places.Little is known about the effects of environmental changes on the biological variation in experimental results. It is postulated that animals from enriched environments can cope better with novel situations, and thus might offer more relevant experimental results with less biological variation.
This project will measure the biological variation in mice in response to routine tests when housed in either standard or enriched environments.

Method and Results
Groups of mice housed under standard and ‘enriched' environments will be subjected to two standard drug development tests:
1) The tetanus toxoid vaccine potency test (a serological method) from the National Institute of Public Health and the Environment (RIVM) and
2) The black and white box test for psychopharmaceuticals. This latter test consists of a black and white compartment. Mice are placed in one of the compartments and the latency and number of entries to the other compartment are measured. This test assesses the effects of drugs on anxiety levels in mice. It can also be used to investigate whether the different housing conditions influence anxiety levels. An anxiolytic drug (Diazepam) will be given to the mice to see whether the enriched housing conditions influence the behavioural effects of this drug. Enrichment will consist of tissues as nesting material, a next box, climbing grid, woodwool, tube (super enriched) or only tissues (enriched). Standard cages are provided with sawdust only.
In each case the biological variation in the results will be compared in the two groups of mice housed under different conditions. Data will also be compared with historical controls.
Expected results (work in progress):Data from previous studies suggest that the effects of enrichment depend on the degree of enrichment and on the mousestrain studied. With regard to the variation in results, data from pilot studies suggest that this may depend on the parameter studied (e.g. physiological or behavioural).

Conclusions and Relevance for 3R
Housing in an enriched environment promotes the welfare of laboratory mice. If housing enrichment has no, or only minor, deleterious effects on the biological variation in results, there is no reason to deny laboratory mice a more natural environment. Moreover, if effects of enrichment lead to less variation in results, the number of animals used per experiment can be reduced. The results of this study will be brought to the attention of regulatory agencies with the aim of influencing future legislation on the housing of laboratory mice.

(see also 3R-INFO-BULLETIN Nr. 22)

Baumans V. Environmental enrichment: practical applications. Proceedings of the 2nd World congress on Alternatives, Utrecht 1996. 1998, 187-191.
Van de Weerd HA & Baumans V. Environmental enrichment in rodents. In: Environmental enrichment information resources for laboratory animals. AWIC Resource Series No 2. 1995, pp 145-149.

Van de Weerd HA, Van Loo PLP, Van Zutphen LFM, Koolhaas JM and Baumans V. Preferences for nesting material as environmental enrichment for laboratory mice. Laboratory Animals 1997, 31:133-143.