Ostriches from the South African Black (SAB) and Zimbabwean Blue (ZB) strains, raised to slaughter age in Oudtshoorn, South Africa, were used to investigate the possibility of improving the growth and survival of commercial ostriches through crossbreeding. Growth data from purebred and crossbred ostriches were analysed to estimate heterotic effects at different age intervals. Heterosis was significant at 1 month (P = 0.017) and 14 months of age (P = 0.03), and approached significance (P < 0.071) at 7, 8 and 13 months of age. Different growth patterns were observed between the two purebred strains, with weight at 14 months differing significantly (SAB 89.6 ± 0.9 kg v. ZB 98.3 ± 4.5 kg). The weight advantage relative to SAB birds at this stage amounted to 10% for ZB, 11% for ZB × SAB and 13% for SAB × ZB (all P < 0.05). Mortality to 30 days also showed significant heterosis (P < 0.05). ZB birds had the highest mortality rate at 0.38 ± 0.03, followed by the SAB × ZB (0.34 ± 0.03), the SAB (0.27 ± 0.01) and the ZB × SAB (0.23 ± 0.02) strains. Results indicate that crossbreeding may be utilised to improve the growth and chick survival of commercial ostriches. The breed combinations should be assessed for other productivity traits to determine the viability of a structured crossbreeding program.