Feeding and management during the rearing period has a major effect on the subsequent performance and welfare of dairy herd replacements. Recently, Carson et al. (2000) found that increasing the live weight of high genetic merit Holstein Friesian heifers from 540 to 620 kg at first calving increased first lactation milk yield by 11%. Mammary growth is a major determinant of milk yield capacity and longevity of lactation and may be the primary driver behind the observed increases in milk production with larger heifers. The first objective of the current study was to evaluate the effects of rearing regime, in terms of diet offered and target weight at 18 months of age, on mammary gland development of high genetic merit Holstein-Friesian heifers. The second objective of this study was to investigate the effect of rearing regime on solear haemorrhages and heel erosions in Holstein-Friesian heifers.