Rodents

Among the tremendous advantages that recommend rodents for research, the ability to control genetic and environmental variables are the most significant. By rearing the animals in controlled environments, it is possible to almost completely eliminate the risks of infectious diseases. This is accomplished by placing the animals in facilities called barrier facilities. These facilities have no windows, which allows control of the exposure to light; the animal rooms are sealed and air entering the rooms is filtered to exclude airborne sources of infection or irritation; food bedding cages and water are sterilized; and caretakers take complete showers before entering these rooms. These precautions reduce the possibility that changes observed with advancing age are due to disease. This makes it more likely that changes are the result of ‘‘normal aging.’’ The development of such barrier facilities led to a doubling of the observed life span of rats and mice over the twenty years from 1970 to 1990. Much of what was once thought to be the inevitable consequence of aging appears to be the consequence of disease. This evolution in health and life span of laboratory animals with improvements in husbandry is reminiscent of the similar changes in human health and life span with the development of improved public health and the advent of antibiotics during the twentieth century.