Effects of caging type and animal source on the development of foot lesions in Sprague Dawley rats (Rattus norvegicus).

Retrospective analysis of data from a chronic (2-year) rat (Rattus norvegicus) carcinogenicity study was performed to compare the incidence of foot lesion development relative to cage type and animal supplier. Groups of rats from two different suppliers were housed in wire-bottom or polycarbonate cages. Clinical observations and body weights were collected. Data were analyzed to determine foot lesion occurrence, time to onset of foot lesions, and body weight change over time. Noteworthy abnormalities of the plantar surface of the hind foot (i.e., ulcers or nodular swellings) were more common in heavier rats than in lighter animals of the same sex (but different source), and abnormalities were more common in rats housed in wire cages than polycarbonate cages. However, despite differences in weight, cage type, and supplier, lesions were not found until the rats had been housed for more than 1 year.