The Animal Core will continue to play a central role in the Nathan Shock Aging Center at the UTHSCSA. Its principal aim is to provide Center Investigators with a spectrum of uniformly maintained, specific-pathogen-free mouse models for the study of aging. It will breed, maintain, and monitor aging colonies of new as well as established rodent models. The Core will determine the longevity of these models, measure life-history and age-sensitive traits, including body weight, body composition, food intake, and morbidity. The Core will distribute animals to Center members for basic research on aging. The Core will continue to be investigator-driven: namely, all models will either 1) be supported by grants or 2) will be selected from those proposed by Center investigators to be the most likely to give insight into fundamental mechanisms of aging and most promising for independent funding.