A triallelic crossbreeding experiment was planned in order to estimate crossbreeding parameters for growth traits (liveweight and daily gain), feed intake and feed conversion from 32 to 60 days. Three selected Spanish strains were involved: maternal lines 11 and 55 and paternal line 44. No significant heterosis estimates were found. Marked direct additive genetic effects of specialized paternal line were contrasted. Purebred differences between Line 44 and the average of maternal lines were plus 90 g on weight at 32 days, plus 325 g at 60 days, plus 12 g/d on daily gain, plus 24 g/d on feed intake and minus 0.18 on feed conversion. Complementarity should be the choice to improve performances of young rabbits during the fattening period.