Four groups of crossbred cows (14 Hereford x Holstein, 14 Angus x Holstein, 15 Simmental x Holstein and 11 Chianina x Holstein) were maintained on two levels of nutrition (high TDN and low TDN) until they produced two weaned calves. The cows started to be bred at their first estrus to Jersey bulls and rebred at first estrous cycles following the first calving to Charolais bulls. Efficiency of production was examined in two ways; 1) Ratio of the weaning weight of calf to the TDN consumed by cow during prepartum and preweaning periods and by calf for preweaning period (El). 2) Ratio of the weaning weight of calf plus weight assessment of cow (5/8 cow weight) to the TDN consumption by cow and by calf for the same duration as in the E1 computation (E2). The ages at first calving were in the order of Hereford, Angus, Simmental and Chianina crossbred cows from the youngest to the oldest. High energy ration group calved six months earlier than low ration group. The difference in the age at first calving was largest between Hereford and Chianina crossbred cows (693 vs. 776 days). Smaller sized cows (Hereford and Angus crossbreds) reached puberty and calving earlier and consumed less TDN, which resulted in being more efficient than larger sized breeding groups. When culled cow weight is included in the product term, the efficiency of production (E2) seemed to be more dependent on the age at first calving for the large sized cows on low ration as judged by the correlation coefficients.