Tang, G., Stewart-Smith, J., Plastow, G., Moore, S., Basarab, J., MacNeil, M. D. and Wang, Z. 2011. Optimizing a beef production system using specialized sire and dam lines. Can. J. Anim. Sci. 91: 353-361. Crossbreeding is an effective method for improving the efficiency of production in commercial cow-calf operations. It exploits available heterosis (hybrid vigour) and complementarity between different breeds or populations (lines). Before adopting a crossbreeding system, commercial cattle producers should evaluate available genetic resources and feasible crossbreeding systems, and choose one that is most beneficial for their own environment, resources, and management. This study compared profitability of alternative crossbreeding systems based on Beefbooster beef cattle breeding strains through computer simulation. Biological and economic data were collected from commercial customers of Beefbooster in Montana and western Canada, and breeding records from the database of Beefbooster, Inc. Three maternal strains (M1, M2 and M4) and two specialized paternal strains (M3 and TX), were evaluated with two simulated crossbreeding systems. System 1 uses a rotational cross between M1 and M4 with yearling crossbred heifers bred to M3 sires. System 2 is based on a three-strain rotation of M1, M2 and M4 with yearling crossbred heifers bred to M3 to facilitate ease of calving and crossbred cows bred to a classical terminal sire strain TX. Simulated base profit from system 2 was $29.57 greater ($215.21 vs. $185.64 yr^-1 per cow) than from system 1.