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Heterosis achieved through well-organized crossbreeding systems can be used to increase weight of calf weaned per cow exposed to breeding by more than 20 percent. Comprehensive programs of breed characterization have revealed large differences among breeds for most biological traits of economic importance. Because of the high percentage of beef cattle in the U.S. and globally that are in herds too small to use well organized crossbreeding systems on a self-contained basis, and because of the wide fluctuation in breed composition between generations in rotational crossbreeding systems, there is need for experimental evaluation of the potential of composite populations as an alternative, or, as a supplement to continuous crossbreeding systems to use heterosis, and, to use genetic differences among breeds for optimizing such biological characters as growth rate and mature size, milk production level, lean-to-fat ratio, and climatic adaptability. The primary objective of achieving and maintaining optimum breed composition is to synchronize cattle genetic resources with the production environment most favored by economic and technological factors and with market requirements.