Growth-related parameters, such as feed intake, growth rate and feed efficiency were investigated in ewe lambs of two genetically related synthetic lines and the Dorper. Ten ewe lambs in each of the three groups were individually fed in metabolism cages and individual intake and mass gain were recorded weekly over a period of 34 weeks, starting at approximately 100 days of age. Intake levels (537o) and mass gain (45.57o) were significantly (P < 0.05) higher in the Dorper as compared to the combined Synthetic group. Both intercept (SL = 0.060 and slope (SL = 0.033) differed between the two groups. After adjusting for differences in mature body mass at equal degrees of maturity, there was still a tendency (SL = 0.060) in the Dorpers to have a higher intake (13.7%) relative to metabolic size and to be less efficient (9.7%) than the Synthetic group (SL = 0.098). No differences in growth rate/M0.75 on equal degrees of maturity were evident, which indicate that differences in growth rate were only related to differences in mature size.