Apparent and true metabolisable energy (ME) values, corrected for zero nitrogen retention, of lucerne and barley were compared in balance studies between young (six months old, 50 to 60 kg BW) and mature (30 months old, 110 to 120 kg BW) ostriches. Birds were housed in individual metabolism crates and excreta collection were performed over a five day period after an adaptation period of seven days. Apparent metabolisable energy, corrected for zero nitrogen retention, (AMEN) of 9.17 +/- 0.251 MJ/kg (lucerne) and 14.24 +/- 0.136 MJ/kg (barley) for young ostriches do not differ (P > 0.05) from values of 8.97 +/- 0.226 MJ/kg (lucerne) and 14.21 +/- 0.134 MJ/kg (barley) obtained for mature ostriches. Also no significant differences occurred between true metabolisable energy, corrected for zero nitrogen retention, (TMEN) values of 9.16 +/- 0.450 MJ/kg (lucerne) and 13.94 +/- 0.390 MJ/kg (barley) for young ostriches and 9.26 +/- 0.412 MJ/kg (lucerne) and 13.92 +/- 0.316 MJ/kg (barley) for mature ostriches. It is concluded that similar AMEN and TMEN values of feedstuffs would be suitable in ostrich diet formulation for age groups older than six months.