A factorial experiment was conducted to investigate the effect of dietary protein level on animal performance, and carcass and meat quality. Eighty-four culled double-muscled Belgian Blue cows, with an initial age and live weight (LW) of 1791 660 days and 659 96 kg, respectively, were used. Maize silage was fed ad libitum and supplemented with concentrate, fed at 10 g/kg of LW. Concentrates were formulated to contain a low or a high DVE-level (110 and 140 g true protein digested in the small intestine/kg dry matter (DM)) and a low or a high OEB-level (-30 and +30 g degraded protein balance in the rumen/kg DM), resulting in average dietary concentrations of 84 (low) and 98 (high) g DVE, and -38 (low) and -11 (high) g OEB/kg DM. Results were split into two classes, being cows with an initial age below or above 4 years. Daily DM intake (P less than or equal to 0.001), net energy intake (P <0.001) and protein intake (P <0.05) were lower for younger cows, while N deposition, efficiencies of utilization of DM and energy, and N deposition were higher, compared with older cows. Daily LW gain (P = 0.108), N deposition (P = 0.076), protein intake (P <0.01) and DM and energy efficiencies (P <0.05) were negatively affected by a low DVE concentration. Daily intake of DM, energy and protein were also negatively affected by a low OEB concentration (P <0.05). The efficiency of N deposition was low, averaging 125 g/kg N intake, but was not affected by DVE, while the dietary OEB level had a significant effect. Few interactions between DVE and OEB occurred, while an interaction between age, DVE and OEB occurred for most intake data. Carcass and meat quality parameters were little affected by the dietary protein supply. The optimum DVE concentration in diets, with a net energy content for fattening of 7.5 MJ/kg DM, is 95-100 g/kg DM for older, as well as for younger, double-muscled cull cows to realize maximum growth rate and feed efficiency. Dietary OEB levels below -15 g/kg DM should be avoided at this DVE concentration to prevent a lower intake. (C) 2004 Elsevier B.V. All rights reserved.