Factors influencing preweaning growth were investigated in a crossbred beef herd reared under intensive pasture conditions. 8731 records were analysed within two farms using the method of least squares. The effect of sire breed, type of dam, age of dam, year, season and sex of calf significantly (P <0.01) influenced birth mass, and all these effects, except season, significantly influenced growth to weaning as measure by average daily gain, actual weaning mass and adjusted 210 day mass. The influence of the sire-effect within the Simmentaler breed was greater than that within the Charolais and Hereford breeds. Significant interaction-effects between sire-breed x sex, sire –breed x year and dam-type x year were establish for birth mass. Growth to weaning was effected by the interaction of sire-breed x dam type, sire-breed x year, sire-breed x season and dam-type x year. Significant regressions on day of birth within the calving season, indicated that birth mass, average daily gain and adjusted 210-day mass increased as the calving season progressed.