If non-additive and additive genetic variation are both important then improvement will be maximized by combining systematic crossbreeding with selection among and within breeds. In this manner, crossbreeding allows for utilization of heterosis and combining of desired characteristics in commercial cattle that would not be present in any parent breed alone.
The purpose of this paper will be to review experimental results relating to choice of breeds. Considerable research has been conducted and much is in progress in the United States, primarily as a result of beef cattle breeding regional projects (W-1, NC-1 and S-10). The parameters of primary importance in choice of breeds are breeding values determined by average gene effects for the breeds and heterosis effects determined by interaction of gene effects and differences in average gene frequency between breeds (Willham, 1969).