Abstract
Age‐associated lesions were characterized in two outbred stocks of barrier‐reared male Sprague‐Dawley rats. Seventy‐two virgin Hap:(SD) between 6–29 months of age and 113 retired breeder Crl:COBS([R])CD([R])(SD) between 12–38 months of age were evaluated for the presence of lesions in all major organ systems. Rats of both stocks developed a spectrum of neoplastic, inflammatory and degenerative diseases with highest prevalence in the oldest age groups. In general, the shorter‐lived Hap:(SD) rats had greater incidences and severity of lesions when compared to Crl:COBS([R])CD([R])SD of similar ages. Many of these differences were not apparent when the two stocks were compared over their respective life spans. The study provides baseline pathology data relevant to the use of these rats in gerontologic research.