The re-use of animals in research: legal, ethical, scientific and managerial aspects

The re-use of animals is a practice that decreases the number of animals used in research (Reduction), but increases the cumulative discomfort imposed on each animal (opposite to Refinement). From an animal welfare point of view, a critical dilemma is present if the point of gravity of the discomfort is in preparative activities, such as preparative surgery, characterization of physiological responses, or training to a task. Re-use extends the life span of the animals that are kept to be re-used, but may seriously jeopardize their welfare. Several laws impose restrictions on the cumulative experimental use of individual animals, but a proper definition was not available until recently. At a managerial level, it should be considered whether one investigator should remain responsible for the extended use of the animal, or that exchange of animals between researchers would be acceptable or desirable. Apart from the wish to reduce the number of animals to be used in research, the suitability of animals for re-use seems very much dependent on their expected life span and economic value. In addition, animal care personnel and management may consider it more rewarding to keep an animal alive after an experiment than to kill it humanely.