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 these animals as unsavory, disease-ridden vermin did not do them any favors. Researchers and scientists rarely use such animals 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 they 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 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 they ingest two hundred times the recommended levels.
Another reason laboratories use rats is genetic consistency. Those raised for animal testing are tested for any genetic defects that may affect the results of the experiments. Only animals with known genetic histories are candidates for testing. Since rats tend to breed frequently, their offspring can also be tested for any genetic abnormalities possibly caused by exposure to the test product. Since the researchers would know of any genetic predispositions towards weight gain or cancer formation, for example, they can safely eliminate these factors as related to the test product.
Because rats reproduce quickly and tend to have large litters, researchers do not have to wait long to evaluate test results in generations. The grandsons and granddaughters of original test animals could appear within months, not the years it would take in human subjects. When looking for potential health hazards, examining various generations of a test subject all at once can provide more definitive proof of a product's safety or potential threat. Overseers such as the Federal Food and Drug Administration (FDA) require this level of proof before even considering human clinical trials. Although the issue of animal testing remains controversial, there can be no doubt that the use of rats in laboratory studies has provided a number of advances in the medical, food and cosmetics industries.