Why rats?

While laboratory tests involving any animal can be fraught with controversy, the scientific community has been using rats experimentally for decades without much vocal objection. Perhaps the reputation of wild rats as unsavory, disease-ridden vermin did not do them any favors. Researchers and scientists rarely use such rats of unknown origin in laboratory tests, however. Carefully bred rats with documented genetic histories are used in animal testing for a number of reasons, including their frequent reproduction, genetic purity and similarities to human biology.

A number of laboratory tests performed on rats involve the safety of chemicals, whether used in medicines, food products or cosmetics. Because rats are mammals, their systems should react to these chemicals in a similar way to those of a human test subject. In order to be considered safe enough for human consumption or exposure, a new chemical compound must first be tested on rats or other mammals. Laboratory rats are often fed extremely high amounts of a new food additive or injected with large doses of a new chemical compound. Theoretically, if the test product is completely safe for humans, it shouldn't matter if the laboratory rats ingest two hundred times the recommended levels.