Data collected from Nguni calves born at the Bartlow Combine Breeding Station were used to investigate factors affecting live weights at birth (1960-1991), 205 days (1960-1991), 365 days (1974-1990) and 540 days (1975-1990) of age. Sire, year of birth, sex of calf and age of dam were found to be highly significant (P < 0.001) sources of variation. The effects of interaction between year of birth and sex of calf and the inbreeding of the calf and dam were significant for some traits but their relative effects were small. A suitable model to describe the data for the respective traits which can be used to calculate genetic parameters and breeding values is constructed and discussed.