The research was carried out in the ALLC "Nadia" of the Chernihiv region on 560 heifers and 648 bulls of the original Ukrainian black- and red-and-white dairy and Jersey breeds and their crosses. It has been established that purebred Jersey heifers from birth to one-year-old are inferior to analogs of the original breeds by 43– 93,5% in live weight and its gains. Crossbred animals of the first and second generations (50, 75%) occupy an intermediate position with a close to additive nature of inheritance with the manifestation of hypothetical heterosis in certain age periods (up to 9,4% in terms of live weight and up to 10,0% in terms of gains). In all age periods, bulls exceed heifers in live weight (up to 15%) and its growth (up to 20%) in general for all breeds and crossbreeds. Sexual dimorphism decreases slightly during the period of intensive puberty of heifers (6–9 months) and increases during puberty of bulls (9–12 months). Young of the Jersey breed, which are smaller in live weight, are distinguished by more pronounced sexual dimorphism in interbreed comparison, which contradicts the Rench allometry rule deduced at the interspecific level. The results of assessing the dynamics of live weight of purebred and crossbred young Jersey breed should be used to clarify growth standards when creating new local and commercial herds.