Module 05 - Research Issues

Choosing the Appropriate Animal Model

Before an animal model is chosen the principal investigator must consider alternatives to the use of live animals in his/her experiment. In line with the CCAC Guidelines on Animal Use Protocol Review, protocol forms should include a declaration that the principal investigator has considered all non-animal alternatives before making the decision to use animals in his/her research.

The most obvious choice of animal species and model for a specific research program may be the same model used by other researchers for the same research. However, with ever increasing numbers of animal models available including new spontaneous mutations, and genetically modified animals constantly being developed, the investigator must consider all factors when selecting the best model for his/her research.

Some of the factors that will influence which animal model the investigator selects are:

• Appropriateness of the model or organ system for the proposed study
• Genetic aspects of the model
• Natural vs. experimentally produced models. Both natural models and induced models of disease are useful depending on the objectives of the study.
• Responses of the animal to procedures
• Environmental aspects important to that particular animal model
• Background information available on the animal and specific model
• Species availability
• Numbers needed, according to statistically appropriate design
• Age and sex needed
• Life span of the animal model
• Size of the animal model
• Cost of both the animal model, and its ongoing care
• Facilities required to house the chosen model appropriately
• Husbandry expertise. Some models require not only special housing, but also special care.

Among these factors are scientific considerations as well as purely practical ones. All are important to the success of the research program.

Once the most appropriate animal model for the research program has been chosen (whether it is a specific mouse strain that will require specialised care and housing, or a conventional farm animal such as a pig), the research scientist should review the many influences (the non-experimental factors) that might potentially affect the outcome of the study. Those factors should be identified and accounted for at all stages to ensure they do not increase the variability or adversely affect the outcome of the experiment.

The many non-experimental factors that can influence the response of the animal model in an experiment can be grouped as follows:

• Animal factors
• Physical / environmental factors
• Husbandry, animal care, and handling factors
• Research manipulation factors

Each group of factors will be discussed in this module, along with suitable examples to emphasise their importance.