Levels of spontaneous malformations in the CD rat and the CD-1 mouse.

Extensive information was supplied about the frequencies and types of spontaneous skeletal and visceral malformations in control and test fetuses which may be encountered during teratological assays. Data were also provided on fertility, agerage body weights, water consumption as a function of diet, and food consumption. The two strains used, Crl:COBS CD (SD) BR (France) rats and Crl:CD-1 (ICR) BR (France) mice, are valuable research tools since they are prolific, have a low rate of spontaneous malformations, and are responsive to teratogenic agents. The difficulties of determining the significance of infrequent anomalies were discussed.