The objective of this study was to assess the growth performance of six cattle breed groups from birth to 18 month of age at Songa Research Station in Rwanda. Records of animals born between 1998 and 2008 were evaluated using nested ANOVA for effects of non-genetic factors on growth performance of different cattle breed groups; compare growth rate of different cattle breed group; and identify suitable breed group for Songa environment. The animals used in the study were taken from a herd of crossbreds of Ankole dams with Brown Swiss, Friesian, Jersey and Sahiwal sires. Birth weight was not affected by breed group, sex of the calf or environmental factors, such as year and season of birth. However, the calves sired by Brown Swiss and Friesians were heavier than calves sired by Jerseys. At weaning, the effects of breed group, year of birth and season of birth were all highly significant (P<0.001), as was the effect of nesting season in breed groups. Weaned calves of Ankole-Friesian crosses (AF) were significantly heavier than those of all other breed groups except Ankole × Brown Swiss (AB) and Ankole × Sahiwal (AS) crossbreds. The heaviest calves were born during season 4 of the year, though weaning weights across seasons did not differ significantly (P>0.05). Male weaned calves (179.3±6.0 kg) were heavier than female weaners (164.6±9.9 kg). A wide range of weaning weight for AB and AF breed groups were observed, compared with the range of mean weights for AJ, AJS, AS, and ASJ suggesting that breed groups containing Jersey and Sahiwal blood are more resilient to environment pressure. Mature weights of animals were significantly affected by breed group (P<0.01), sex (P<0.001), and year of birth (P<0.001) while season and its interaction with breed group (P>0.05) did not influence it. Generally, breed group AB grew faster than all other breed groups while the lowest growth rate was registered in breed group AS. However, the speed of growth was similar to those in breed groups AJ, AJS, AS and AJS. We observe that AS, AJS and ASJ breed group was the best breed group for the area of study and that the major factors to consider during the breeding of the various breed groups include sex, season of birth and year of birth. It is therefore recommended that to attain the best level of performance for these cattle, artificial insemination should be synchronized with maximum forage availability at parturition