Economical and biological efficiencies of beef production to weaning and to slaughter were estimated in three groups, different in milk available (low, medium, and high) to the calves but with the same potential for growth. Data from different breed groups of cows (low [L] = Hereford x Angus, medium [M] = Red Poll x Angus, and high [H] = Milking Shorthorn x Angus) were used. Economical efficiency was the ratio of income to expenses and biological efficiency was the ratio of calf weight to total feed energy required. Income was derived from cull cows and calves at weaning or carcasses of calves fed to slaughter. Feed and non-feed expenses for the cowherd and for calves to weaning or to slaughter were included in economical efficiency. Efficiencies were estimated assuming observed reproductive rates and energy requirements for maintenance, as well as for equal reproductive rates and equal energy requirements for maintenance in the M and H groups. With the observed reproductive rates and maintenance requirements, biological efficiencies to weaning and to slaughter were 28.1, 27.2, and 27.5 g of weaning weight and 22.0, 20.4, and 20.3 g of carcass weight per megacalorie of ME for L, M, and H, respectively; the corresponding values using equal reproduction and equal maintenance in M and H were 28.3, 27.2, and 27.4 g of weaning weight and 22.1, 20.5, and 20.5 g of carcass weight per megacalorie of ME.(ABSTRACT TRUNCATED AT 250 WORDS)